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Massage the documentation for KVM_X86_QUIRK_SLOT_ZAP_ALL to call out that
it applies to moved memslots as well as deleted memslots, to avoid KVM's
"fast zap" terminology (which has no meaning for userspace), and to reword
the documented targeted zap behavior to specifically say that KVM _may_
zap a subset of all SPTEs. As evidenced by the fix to zap non-leafs SPTEs
with gPTEs, formally documenting KVM's exact internal behavior is risky
and unnecessary.
Signed-off-by: Sean Christopherson <seanjc@google.com>
Message-ID: <20241009192345.1148353-4-seanjc@google.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
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The last use of kvm_vcpu_gfn_to_pfn_atomic was removed by commit
1bbc60d0c7e5 ("KVM: x86/mmu: Remove MMU auditing")
Remove it.
Signed-off-by: Dr. David Alan Gilbert <linux@treblig.org>
Message-ID: <20241001141354.18009-3-linux@treblig.org>
[Adjust Documentation/virt/kvm/locking.rst. - Paolo]
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
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Pull x86 kvm updates from Paolo Bonzini:
"x86:
- KVM currently invalidates the entirety of the page tables, not just
those for the memslot being touched, when a memslot is moved or
deleted.
This does not traditionally have particularly noticeable overhead,
but Intel's TDX will require the guest to re-accept private pages
if they are dropped from the secure EPT, which is a non starter.
Actually, the only reason why this is not already being done is a
bug which was never fully investigated and caused VM instability
with assigned GeForce GPUs, so allow userspace to opt into the new
behavior.
- Advertise AVX10.1 to userspace (effectively prep work for the
"real" AVX10 functionality that is on the horizon)
- Rework common MSR handling code to suppress errors on userspace
accesses to unsupported-but-advertised MSRs
This will allow removing (almost?) all of KVM's exemptions for
userspace access to MSRs that shouldn't exist based on the vCPU
model (the actual cleanup is non-trivial future work)
- Rework KVM's handling of x2APIC ICR, again, because AMD (x2AVIC)
splits the 64-bit value into the legacy ICR and ICR2 storage,
whereas Intel (APICv) stores the entire 64-bit value at the ICR
offset
- Fix a bug where KVM would fail to exit to userspace if one was
triggered by a fastpath exit handler
- Add fastpath handling of HLT VM-Exit to expedite re-entering the
guest when there's already a pending wake event at the time of the
exit
- Fix a WARN caused by RSM entering a nested guest from SMM with
invalid guest state, by forcing the vCPU out of guest mode prior to
signalling SHUTDOWN (the SHUTDOWN hits the VM altogether, not the
nested guest)
- Overhaul the "unprotect and retry" logic to more precisely identify
cases where retrying is actually helpful, and to harden all retry
paths against putting the guest into an infinite retry loop
- Add support for yielding, e.g. to honor NEED_RESCHED, when zapping
rmaps in the shadow MMU
- Refactor pieces of the shadow MMU related to aging SPTEs in
prepartion for adding multi generation LRU support in KVM
- Don't stuff the RSB after VM-Exit when RETPOLINE=y and AutoIBRS is
enabled, i.e. when the CPU has already flushed the RSB
- Trace the per-CPU host save area as a VMCB pointer to improve
readability and cleanup the retrieval of the SEV-ES host save area
- Remove unnecessary accounting of temporary nested VMCB related
allocations
- Set FINAL/PAGE in the page fault error code for EPT violations if
and only if the GVA is valid. If the GVA is NOT valid, there is no
guest-side page table walk and so stuffing paging related metadata
is nonsensical
- Fix a bug where KVM would incorrectly synthesize a nested VM-Exit
instead of emulating posted interrupt delivery to L2
- Add a lockdep assertion to detect unsafe accesses of vmcs12
structures
- Harden eVMCS loading against an impossible NULL pointer deref
(really truly should be impossible)
- Minor SGX fix and a cleanup
- Misc cleanups
Generic:
- Register KVM's cpuhp and syscore callbacks when enabling
virtualization in hardware, as the sole purpose of said callbacks
is to disable and re-enable virtualization as needed
- Enable virtualization when KVM is loaded, not right before the
first VM is created
Together with the previous change, this simplifies a lot the logic
of the callbacks, because their very existence implies
virtualization is enabled
- Fix a bug that results in KVM prematurely exiting to userspace for
coalesced MMIO/PIO in many cases, clean up the related code, and
add a testcase
- Fix a bug in kvm_clear_guest() where it would trigger a buffer
overflow _if_ the gpa+len crosses a page boundary, which thankfully
is guaranteed to not happen in the current code base. Add WARNs in
more helpers that read/write guest memory to detect similar bugs
Selftests:
- Fix a goof that caused some Hyper-V tests to be skipped when run on
bare metal, i.e. NOT in a VM
- Add a regression test for KVM's handling of SHUTDOWN for an SEV-ES
guest
- Explicitly include one-off assets in .gitignore. Past Sean was
completely wrong about not being able to detect missing .gitignore
entries
- Verify userspace single-stepping works when KVM happens to handle a
VM-Exit in its fastpath
- Misc cleanups"
* tag 'for-linus' of git://git.kernel.org/pub/scm/virt/kvm/kvm: (127 commits)
Documentation: KVM: fix warning in "make htmldocs"
s390: Enable KVM_S390_UCONTROL config in debug_defconfig
selftests: kvm: s390: Add VM run test case
KVM: SVM: let alternatives handle the cases when RSB filling is required
KVM: VMX: Set PFERR_GUEST_{FINAL,PAGE}_MASK if and only if the GVA is valid
KVM: x86/mmu: Use KVM_PAGES_PER_HPAGE() instead of an open coded equivalent
KVM: x86/mmu: Add KVM_RMAP_MANY to replace open coded '1' and '1ul' literals
KVM: x86/mmu: Fold mmu_spte_age() into kvm_rmap_age_gfn_range()
KVM: x86/mmu: Morph kvm_handle_gfn_range() into an aging specific helper
KVM: x86/mmu: Honor NEED_RESCHED when zapping rmaps and blocking is allowed
KVM: x86/mmu: Add a helper to walk and zap rmaps for a memslot
KVM: x86/mmu: Plumb a @can_yield parameter into __walk_slot_rmaps()
KVM: x86/mmu: Move walk_slot_rmaps() up near for_each_slot_rmap_range()
KVM: x86/mmu: WARN on MMIO cache hit when emulating write-protected gfn
KVM: x86/mmu: Detect if unprotect will do anything based on invalid_list
KVM: x86/mmu: Subsume kvm_mmu_unprotect_page() into the and_retry() version
KVM: x86: Rename reexecute_instruction()=>kvm_unprotect_and_retry_on_failure()
KVM: x86: Update retry protection fields when forcing retry on emulation failure
KVM: x86: Apply retry protection to "unprotect on failure" path
KVM: x86: Check EMULTYPE_WRITE_PF_TO_SP before unprotecting gfn
...
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The warning
Documentation/virt/kvm/locking.rst:31: ERROR: Unexpected indentation.
is caused by incorrectly treating a line as the continuation of a paragraph,
rather than as the first line in a bullet list.
Fixed: 44d174596260 ("KVM: Use dedicated mutex to protect kvm_usage_count to avoid deadlock")
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
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KVM VMX changes for 6.12:
- Set FINAL/PAGE in the page fault error code for EPT Violations if and only
if the GVA is valid. If the GVA is NOT valid, there is no guest-side page
table walk and so stuffing paging related metadata is nonsensical.
- Fix a bug where KVM would incorrectly synthesize a nested VM-Exit instead of
emulating posted interrupt delivery to L2.
- Add a lockdep assertion to detect unsafe accesses of vmcs12 structures.
- Harden eVMCS loading against an impossible NULL pointer deref (really truly
should be impossible).
- Minor SGX fix and a cleanup.
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Synthesize a consistency check VM-Exit (VM-Enter) or VM-Abort (VM-Exit) if
L1 attempts to load/store an MSR via the VMCS MSR lists that userspace has
disallowed access to via an MSR filter. Intel already disallows including
a handful of "special" MSRs in the VMCS lists, so denying access isn't
completely without precedent.
More importantly, the behavior is well-defined _and_ can be communicated
the end user, e.g. to the customer that owns a VM running as L1 on top of
KVM. On the other hand, ignoring userspace MSR filters is all but
guaranteed to result in unexpected behavior as the access will hit KVM's
internal state, which is likely not up-to-date.
Unlike KVM-internal accesses, instruction emulation, and dedicated VMCS
fields, the MSRs in the VMCS load/store lists are 100% guest controlled,
thus making it all but impossible to reason about the correctness of
ignoring the MSR filter. And if userspace *really* wants to deny access
to MSRs via the aforementioned scenarios, userspace can hide the
associated feature from the guest, e.g. by disabling the PMU to prevent
accessing PERF_GLOBAL_CTRL via its VMCS field. But for the MSR lists, KVM
is blindly processing MSRs; the MSR filters are the _only_ way for
userspace to deny access.
This partially reverts commit ac8d6cad3c7b ("KVM: x86: Only do MSR
filtering when access MSR by rdmsr/wrmsr").
Cc: Hou Wenlong <houwenlong.hwl@antgroup.com>
Cc: Jim Mattson <jmattson@google.com>
Link: https://lore.kernel.org/r/20240722235922.3351122-1-seanjc@google.com
Signed-off-by: Sean Christopherson <seanjc@google.com>
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Register KVM's cpuhp and syscore callback when enabling virtualization
in hardware instead of registering the callbacks during initialization,
and let the CPU up/down framework invoke the inner enable/disable
functions. Registering the callbacks during initialization makes things
more complex than they need to be, as KVM needs to be very careful about
handling races between enabling CPUs being onlined/offlined and hardware
being enabled/disabled.
Intel TDX support will require KVM to enable virtualization during KVM
initialization, i.e. will add another wrinkle to things, at which point
sorting out the potential races with kvm_usage_count would become even
more complex.
Note, using the cpuhp framework has a subtle behavioral change: enabling
will be done serially across all CPUs, whereas KVM currently sends an IPI
to all CPUs in parallel. While serializing virtualization enabling could
create undesirable latency, the issue is limited to the 0=>1 transition of
VM creation. And even that can be mitigated, e.g. by letting userspace
force virtualization to be enabled when KVM is initialized.
Cc: Chao Gao <chao.gao@intel.com>
Reviewed-by: Kai Huang <kai.huang@intel.com>
Acked-by: Kai Huang <kai.huang@intel.com>
Tested-by: Farrah Chen <farrah.chen@intel.com>
Signed-off-by: Sean Christopherson <seanjc@google.com>
Message-ID: <20240830043600.127750-3-seanjc@google.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
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Use a dedicated mutex to guard kvm_usage_count to fix a potential deadlock
on x86 due to a chain of locks and SRCU synchronizations. Translating the
below lockdep splat, CPU1 #6 will wait on CPU0 #1, CPU0 #8 will wait on
CPU2 #3, and CPU2 #7 will wait on CPU1 #4 (if there's a writer, due to the
fairness of r/w semaphores).
CPU0 CPU1 CPU2
1 lock(&kvm->slots_lock);
2 lock(&vcpu->mutex);
3 lock(&kvm->srcu);
4 lock(cpu_hotplug_lock);
5 lock(kvm_lock);
6 lock(&kvm->slots_lock);
7 lock(cpu_hotplug_lock);
8 sync(&kvm->srcu);
Note, there are likely more potential deadlocks in KVM x86, e.g. the same
pattern of taking cpu_hotplug_lock outside of kvm_lock likely exists with
__kvmclock_cpufreq_notifier():
cpuhp_cpufreq_online()
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-> cpufreq_online()
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-> cpufreq_gov_performance_limits()
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-> __cpufreq_driver_target()
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-> __target_index()
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-> cpufreq_freq_transition_begin()
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-> cpufreq_notify_transition()
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-> ... __kvmclock_cpufreq_notifier()
But, actually triggering such deadlocks is beyond rare due to the
combination of dependencies and timings involved. E.g. the cpufreq
notifier is only used on older CPUs without a constant TSC, mucking with
the NX hugepage mitigation while VMs are running is very uncommon, and
doing so while also onlining/offlining a CPU (necessary to generate
contention on cpu_hotplug_lock) would be even more unusual.
The most robust solution to the general cpu_hotplug_lock issue is likely
to switch vm_list to be an RCU-protected list, e.g. so that x86's cpufreq
notifier doesn't to take kvm_lock. For now, settle for fixing the most
blatant deadlock, as switching to an RCU-protected list is a much more
involved change, but add a comment in locking.rst to call out that care
needs to be taken when walking holding kvm_lock and walking vm_list.
======================================================
WARNING: possible circular locking dependency detected
6.10.0-smp--c257535a0c9d-pip #330 Tainted: G S O
------------------------------------------------------
tee/35048 is trying to acquire lock:
ff6a80eced71e0a8 (&kvm->slots_lock){+.+.}-{3:3}, at: set_nx_huge_pages+0x179/0x1e0 [kvm]
but task is already holding lock:
ffffffffc07abb08 (kvm_lock){+.+.}-{3:3}, at: set_nx_huge_pages+0x14a/0x1e0 [kvm]
which lock already depends on the new lock.
the existing dependency chain (in reverse order) is:
-> #3 (kvm_lock){+.+.}-{3:3}:
__mutex_lock+0x6a/0xb40
mutex_lock_nested+0x1f/0x30
kvm_dev_ioctl+0x4fb/0xe50 [kvm]
__se_sys_ioctl+0x7b/0xd0
__x64_sys_ioctl+0x21/0x30
x64_sys_call+0x15d0/0x2e60
do_syscall_64+0x83/0x160
entry_SYSCALL_64_after_hwframe+0x76/0x7e
-> #2 (cpu_hotplug_lock){++++}-{0:0}:
cpus_read_lock+0x2e/0xb0
static_key_slow_inc+0x16/0x30
kvm_lapic_set_base+0x6a/0x1c0 [kvm]
kvm_set_apic_base+0x8f/0xe0 [kvm]
kvm_set_msr_common+0x9ae/0xf80 [kvm]
vmx_set_msr+0xa54/0xbe0 [kvm_intel]
__kvm_set_msr+0xb6/0x1a0 [kvm]
kvm_arch_vcpu_ioctl+0xeca/0x10c0 [kvm]
kvm_vcpu_ioctl+0x485/0x5b0 [kvm]
__se_sys_ioctl+0x7b/0xd0
__x64_sys_ioctl+0x21/0x30
x64_sys_call+0x15d0/0x2e60
do_syscall_64+0x83/0x160
entry_SYSCALL_64_after_hwframe+0x76/0x7e
-> #1 (&kvm->srcu){.+.+}-{0:0}:
__synchronize_srcu+0x44/0x1a0
synchronize_srcu_expedited+0x21/0x30
kvm_swap_active_memslots+0x110/0x1c0 [kvm]
kvm_set_memslot+0x360/0x620 [kvm]
__kvm_set_memory_region+0x27b/0x300 [kvm]
kvm_vm_ioctl_set_memory_region+0x43/0x60 [kvm]
kvm_vm_ioctl+0x295/0x650 [kvm]
__se_sys_ioctl+0x7b/0xd0
__x64_sys_ioctl+0x21/0x30
x64_sys_call+0x15d0/0x2e60
do_syscall_64+0x83/0x160
entry_SYSCALL_64_after_hwframe+0x76/0x7e
-> #0 (&kvm->slots_lock){+.+.}-{3:3}:
__lock_acquire+0x15ef/0x2e30
lock_acquire+0xe0/0x260
__mutex_lock+0x6a/0xb40
mutex_lock_nested+0x1f/0x30
set_nx_huge_pages+0x179/0x1e0 [kvm]
param_attr_store+0x93/0x100
module_attr_store+0x22/0x40
sysfs_kf_write+0x81/0xb0
kernfs_fop_write_iter+0x133/0x1d0
vfs_write+0x28d/0x380
ksys_write+0x70/0xe0
__x64_sys_write+0x1f/0x30
x64_sys_call+0x281b/0x2e60
do_syscall_64+0x83/0x160
entry_SYSCALL_64_after_hwframe+0x76/0x7e
Cc: Chao Gao <chao.gao@intel.com>
Fixes: 0bf50497f03b ("KVM: Drop kvm_count_lock and instead protect kvm_usage_count with kvm_lock")
Cc: stable@vger.kernel.org
Reviewed-by: Kai Huang <kai.huang@intel.com>
Acked-by: Kai Huang <kai.huang@intel.com>
Tested-by: Farrah Chen <farrah.chen@intel.com>
Signed-off-by: Sean Christopherson <seanjc@google.com>
Message-ID: <20240830043600.127750-2-seanjc@google.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
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Introduce the quirk KVM_X86_QUIRK_SLOT_ZAP_ALL to allow users to select
KVM's behavior when a memslot is moved or deleted for KVM_X86_DEFAULT_VM
VMs. Make sure KVM behave as if the quirk is always disabled for
non-KVM_X86_DEFAULT_VM VMs.
The KVM_X86_QUIRK_SLOT_ZAP_ALL quirk offers two behavior options:
- when enabled: Invalidate/zap all SPTEs ("zap-all"),
- when disabled: Precisely zap only the leaf SPTEs within the range of the
moving/deleting memory slot ("zap-slot-leafs-only").
"zap-all" is today's KVM behavior to work around a bug [1] where the
changing the zapping behavior of memslot move/deletion would cause VM
instability for VMs with an Nvidia GPU assigned; while
"zap-slot-leafs-only" allows for more precise zapping of SPTEs within the
memory slot range, improving performance in certain scenarios [2], and
meeting the functional requirements for TDX.
Previous attempts to select "zap-slot-leafs-only" include a per-VM
capability approach [3] (which was not preferred because the root cause of
the bug remained unidentified) and a per-memslot flag approach [4]. Sean
and Paolo finally recommended the implementation of this quirk and
explained that it's the least bad option [5].
By default, the quirk is enabled on KVM_X86_DEFAULT_VM VMs to use
"zap-all". Users have the option to disable the quirk to select
"zap-slot-leafs-only" for specific KVM_X86_DEFAULT_VM VMs that are
unaffected by this bug.
For non-KVM_X86_DEFAULT_VM VMs, the "zap-slot-leafs-only" behavior is
always selected without user's opt-in, regardless of if the user opts for
"zap-all".
This is because it is assumed until proven otherwise that non-
KVM_X86_DEFAULT_VM VMs will not be exposed to the bug [1], and most
importantly, it's because TDX must have "zap-slot-leafs-only" always
selected. In TDX's case a memslot's GPA range can be a mixture of "private"
or "shared" memory. Shared is roughly analogous to how EPT is handled for
normal VMs, but private GPAs need lots of special treatment:
1) "zap-all" would require to zap private root page or non-leaf entries or
at least leaf-entries beyond the deleting memslot scope. However, TDX
demands that the root page of the private page table remains unchanged,
with leaf entries being zapped before non-leaf entries, and any dropped
private guest pages must be re-accepted by the guest.
2) if "zap-all" zaps only shared page tables, it would result in private
pages still being mapped when the memslot is gone. This may affect even
other processes if later the gmem fd was whole punched, causing the
pages being freed on the host while still mapped in the TD, because
there's no pgoff to the gfn information to zap the private page table
after memslot is gone.
So, simply go "zap-slot-leafs-only" as if the quirk is always disabled for
non-KVM_X86_DEFAULT_VM VMs to avoid manual opt-in for every VM type [6] or
complicating quirk disabling interface (current quirk disabling interface
is limited, no way to query quirks, or force them to be disabled).
Add a new function kvm_mmu_zap_memslot_leafs() to implement
"zap-slot-leafs-only". This function does not call kvm_unmap_gfn_range(),
bypassing special handling to APIC_ACCESS_PAGE_PRIVATE_MEMSLOT, as
1) The APIC_ACCESS_PAGE_PRIVATE_MEMSLOT cannot be created by users, nor can
it be moved. It is only deleted by KVM when APICv is permanently
inhibited.
2) kvm_vcpu_reload_apic_access_page() effectively does nothing when
APIC_ACCESS_PAGE_PRIVATE_MEMSLOT is deleted.
3) Avoid making all cpus request of KVM_REQ_APIC_PAGE_RELOAD can save on
costly IPIs.
Suggested-by: Kai Huang <kai.huang@intel.com>
Suggested-by: Sean Christopherson <seanjc@google.com>
Suggested-by: Paolo Bonzini <pbonzini@redhat.com>
Link: https://patchwork.kernel.org/project/kvm/patch/20190205210137.1377-11-sean.j.christopherson@intel.com [1]
Link: https://patchwork.kernel.org/project/kvm/patch/20190205210137.1377-11-sean.j.christopherson@intel.com/#25054908 [2]
Link: https://lore.kernel.org/kvm/20200713190649.GE29725@linux.intel.com/T/#mabc0119583dacf621025e9d873c85f4fbaa66d5c [3]
Link: https://lore.kernel.org/all/20240515005952.3410568-3-rick.p.edgecombe@intel.com [4]
Link: https://lore.kernel.org/all/7df9032d-83e4-46a1-ab29-6c7973a2ab0b@redhat.com [5]
Link: https://lore.kernel.org/all/ZnGa550k46ow2N3L@google.com [6]
Co-developed-by: Rick Edgecombe <rick.p.edgecombe@intel.com>
Signed-off-by: Rick Edgecombe <rick.p.edgecombe@intel.com>
Signed-off-by: Yan Zhao <yan.y.zhao@intel.com>
Message-ID: <20240703021043.13881-1-yan.y.zhao@intel.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
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Pull documentation update from Jonathan Corbet:
"Another relatively mundane cycle for docs:
- The beginning of an EEVDF scheduler document
- More Chinese translations
- A rethrashing of our bisection documentation
...plus the usual array of smaller fixes, and more than the usual
number of typo fixes"
* tag 'docs-6.12' of git://git.lwn.net/linux: (48 commits)
Remove duplicate "and" in 'Linux NVMe docs.
docs:filesystems: fix spelling and grammar mistakes
docs:filesystem: fix mispelled words on autofs page
docs:mm: fixed spelling and grammar mistakes on vmalloc kernel stack page
Documentation: PCI: fix typo in pci.rst
docs/zh_CN: add the translation of kbuild/gcc-plugins.rst
docs/process: fix typos
docs:mm: fix spelling mistakes in heterogeneous memory management page
accel/qaic: Fix a typo
docs/zh_CN: update the translation of security-bugs
docs: block: Fix grammar and spelling mistakes in bfq-iosched.rst
Documentation: Fix spelling mistakes
Documentation/gpu: Fix typo in Documentation/gpu/komeda-kms.rst
scripts: sphinx-pre-install: remove unnecessary double check for $cur_version
Loongarch: KVM: Add KVM hypercalls documentation for LoongArch
Documentation: Document the kernel flag bdev_allow_write_mounted
docs: scheduler: completion: Update member of struct completion
docs: kerneldoc-preamble.sty: Suppress extra spaces in CJK literal blocks
docs: submitting-patches: Advertise b4
docs: update dev-tools/kcsan.rst url about KTSAN
...
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Add documentation topic for using pv_virt when running as a guest
on KVM hypervisor.
Signed-off-by: Bibo Mao <maobibo@loongson.cn>
Signed-off-by: Xianglai Li <lixianglai@loongson.cn>
Co-developed-by: Mingcong Bai <jeffbai@aosc.io>
Signed-off-by: Mingcong Bai <jeffbai@aosc.io>
Link: https://lore.kernel.org/all/5c338084b1bcccc1d57dce9ddb1e7081@aosc.io/
Signed-off-by: Dandan Zhang <zhangdandan@uniontech.com>
[jc: fixed htmldocs build error]
Signed-off-by: Jonathan Corbet <corbet@lwn.net>
Link: https://lore.kernel.org/r/4769C036576F8816+20240828045950.3484113-1-zhangdandan@uniontech.com
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git://git.kernel.org/pub/scm/linux/kernel/git/arm64/linux
Pull arm64 updates from Will Deacon:
"The highlights are support for Arm's "Permission Overlay Extension"
using memory protection keys, support for running as a protected guest
on Android as well as perf support for a bunch of new interconnect
PMUs.
Summary:
ACPI:
- Enable PMCG erratum workaround for HiSilicon HIP10 and 11
platforms.
- Ensure arm64-specific IORT header is covered by MAINTAINERS.
CPU Errata:
- Enable workaround for hardware access/dirty issue on Ampere-1A
cores.
Memory management:
- Define PHYSMEM_END to fix a crash in the amdgpu driver.
- Avoid tripping over invalid kernel mappings on the kexec() path.
- Userspace support for the Permission Overlay Extension (POE) using
protection keys.
Perf and PMUs:
- Add support for the "fixed instruction counter" extension in the
CPU PMU architecture.
- Extend and fix the event encodings for Apple's M1 CPU PMU.
- Allow LSM hooks to decide on SPE permissions for physical
profiling.
- Add support for the CMN S3 and NI-700 PMUs.
Confidential Computing:
- Add support for booting an arm64 kernel as a protected guest under
Android's "Protected KVM" (pKVM) hypervisor.
Selftests:
- Fix vector length issues in the SVE/SME sigreturn tests
- Fix build warning in the ptrace tests.
Timers:
- Add support for PR_{G,S}ET_TSC so that 'rr' can deal with
non-determinism arising from the architected counter.
Miscellaneous:
- Rework our IPI-based CPU stopping code to try NMIs if regular IPIs
don't succeed.
- Minor fixes and cleanups"
* tag 'arm64-upstream' of git://git.kernel.org/pub/scm/linux/kernel/git/arm64/linux: (94 commits)
perf: arm-ni: Fix an NULL vs IS_ERR() bug
arm64: hibernate: Fix warning for cast from restricted gfp_t
arm64: esr: Define ESR_ELx_EC_* constants as UL
arm64: pkeys: remove redundant WARN
perf: arm_pmuv3: Use BR_RETIRED for HW branch event if enabled
MAINTAINERS: List Arm interconnect PMUs as supported
perf: Add driver for Arm NI-700 interconnect PMU
dt-bindings/perf: Add Arm NI-700 PMU
perf/arm-cmn: Improve format attr printing
perf/arm-cmn: Clean up unnecessary NUMA_NO_NODE check
arm64/mm: use lm_alias() with addresses passed to memblock_free()
mm: arm64: document why pte is not advanced in contpte_ptep_set_access_flags()
arm64: Expose the end of the linear map in PHYSMEM_END
arm64: trans_pgd: mark PTEs entries as valid to avoid dead kexec()
arm64/mm: Delete __init region from memblock.reserved
perf/arm-cmn: Support CMN S3
dt-bindings: perf: arm-cmn: Add CMN S3
perf/arm-cmn: Refactor DTC PMU register access
perf/arm-cmn: Make cycle counts less surprising
perf/arm-cmn: Improve build-time assertion
...
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Hook up pKVM's MMIO_GUARD hypercall so that ioremap() and friends will
register the target physical address as MMIO with the hypervisor,
allowing guest exits to that page to be emulated by the host with full
syndrome information.
Acked-by: Marc Zyngier <maz@kernel.org>
Link: https://lore.kernel.org/r/20240830130150.8568-7-will@kernel.org
Signed-off-by: Will Deacon <will@kernel.org>
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If we detect the presence of pKVM's SHARE and UNSHARE hypercalls, then
register a backend implementation of the mem_encrypt API so that things
like DMA buffers can be shared appropriately with the host.
Acked-by: Marc Zyngier <maz@kernel.org>
Link: https://lore.kernel.org/r/20240830130150.8568-5-will@kernel.org
Signed-off-by: Will Deacon <will@kernel.org>
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Implement a pKVM protected guest driver to probe the presence of pKVM
and determine the memory protection granule using the HYP_MEMINFO
hypercall.
Acked-by: Marc Zyngier <maz@kernel.org>
Link: https://lore.kernel.org/r/20240830130150.8568-3-will@kernel.org
Signed-off-by: Will Deacon <will@kernel.org>
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git://git.kernel.org/pub/scm/linux/kernel/git/kvmarm/kvmarm into HEAD
KVM/arm64 fixes for 6.11, round #1
- Use kvfree() for the kvmalloc'd nested MMUs array
- Set of fixes to address warnings in W=1 builds
- Make KVM depend on assembler support for ARMv8.4
- Fix for vgic-debug interface for VMs without LPIs
- Actually check ID_AA64MMFR3_EL1.S1PIE in get-reg-list selftest
- Minor code / comment cleanups for configuring PAuth traps
- Take kvm->arch.config_lock to prevent destruction / initialization
race for a vCPU's CPUIF which may lead to a UAF
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Fixes the register ID of SPSR_FIQ.
SPSR_FIQ is a 64-bit register and the 64-bit register size mask is
0x0030000000000000ULL.
Fixes: fd3bc912d3d1 ("KVM: Documentation: Document arm64 core registers in detail")
Signed-off-by: Takahiro Itazuri <itazur@amazon.com>
Acked-by: Marc Zyngier <maz@kernel.org>
Link: https://lore.kernel.org/r/20230606154628.95498-1-itazur@amazon.com
Signed-off-by: Oliver Upton <oliver.upton@linux.dev>
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* fix latent bug in how usage of large pages is determined for
confidential VMs
* fix "underline too short" in docs
* eliminate log spam from limited APIC timer periods
* disallow pre-faulting of memory before SEV-SNP VMs are initialized
* delay clearing and encrypting private memory until it is added to
guest page tables
* this change also enables another small cleanup: the checks in
SNP_LAUNCH_UPDATE that limit it to non-populated, private pages
can now be moved in the common kvm_gmem_populate() function
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KVM_PRE_FAULT_MEMORY for an SNP guest can race with
sev_gmem_post_populate() in bad ways. The following sequence for
instance can potentially trigger an RMP fault:
thread A, sev_gmem_post_populate: called
thread B, sev_gmem_prepare: places below 'pfn' in a private state in RMP
thread A, sev_gmem_post_populate: *vaddr = kmap_local_pfn(pfn + i);
thread A, sev_gmem_post_populate: copy_from_user(vaddr, src + i * PAGE_SIZE, PAGE_SIZE);
RMP #PF
Fix this by only allowing KVM_PRE_FAULT_MEMORY to run after a guest's
initial private memory contents have been finalized via
KVM_SEV_SNP_LAUNCH_FINISH.
Beyond fixing this issue, it just sort of makes sense to enforce this,
since the KVM_PRE_FAULT_MEMORY documentation states:
"KVM maps memory as if the vCPU generated a stage-2 read page fault"
which sort of implies we should be acting on the same guest state that a
vCPU would see post-launch after the initial guest memory is all set up.
Co-developed-by: Michael Roth <michael.roth@amd.com>
Signed-off-by: Michael Roth <michael.roth@amd.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
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Fix "WARNING: Title underline too short" by extending title line to the
proper length.
Signed-off-by: Chang Yu <marcus.yu.56@gmail.com>
Message-ID: <ZqB3lofbzMQh5Q-5@gmail.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
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Pull kvm updates from Paolo Bonzini:
"ARM:
- Initial infrastructure for shadow stage-2 MMUs, as part of nested
virtualization enablement
- Support for userspace changes to the guest CTR_EL0 value, enabling
(in part) migration of VMs between heterogenous hardware
- Fixes + improvements to pKVM's FF-A proxy, adding support for v1.1
of the protocol
- FPSIMD/SVE support for nested, including merged trap configuration
and exception routing
- New command-line parameter to control the WFx trap behavior under
KVM
- Introduce kCFI hardening in the EL2 hypervisor
- Fixes + cleanups for handling presence/absence of FEAT_TCRX
- Miscellaneous fixes + documentation updates
LoongArch:
- Add paravirt steal time support
- Add support for KVM_DIRTY_LOG_INITIALLY_SET
- Add perf kvm-stat support for loongarch
RISC-V:
- Redirect AMO load/store access fault traps to guest
- perf kvm stat support
- Use guest files for IMSIC virtualization, when available
s390:
- Assortment of tiny fixes which are not time critical
x86:
- Fixes for Xen emulation
- Add a global struct to consolidate tracking of host values, e.g.
EFER
- Add KVM_CAP_X86_APIC_BUS_CYCLES_NS to allow configuring the
effective APIC bus frequency, because TDX
- Print the name of the APICv/AVIC inhibits in the relevant
tracepoint
- Clean up KVM's handling of vendor specific emulation to
consistently act on "compatible with Intel/AMD", versus checking
for a specific vendor
- Drop MTRR virtualization, and instead always honor guest PAT on
CPUs that support self-snoop
- Update to the newfangled Intel CPU FMS infrastructure
- Don't advertise IA32_PERF_GLOBAL_OVF_CTRL as an MSR-to-be-saved, as
it reads '0' and writes from userspace are ignored
- Misc cleanups
x86 - MMU:
- Small cleanups, renames and refactoring extracted from the upcoming
Intel TDX support
- Don't allocate kvm_mmu_page.shadowed_translation for shadow pages
that can't hold leafs SPTEs
- Unconditionally drop mmu_lock when allocating TDP MMU page tables
for eager page splitting, to avoid stalling vCPUs when splitting
huge pages
- Bug the VM instead of simply warning if KVM tries to split a SPTE
that is non-present or not-huge. KVM is guaranteed to end up in a
broken state because the callers fully expect a valid SPTE, it's
all but dangerous to let more MMU changes happen afterwards
x86 - AMD:
- Make per-CPU save_area allocations NUMA-aware
- Force sev_es_host_save_area() to be inlined to avoid calling into
an instrumentable function from noinstr code
- Base support for running SEV-SNP guests. API-wise, this includes a
new KVM_X86_SNP_VM type, encrypting/measure the initial image into
guest memory, and finalizing it before launching it. Internally,
there are some gmem/mmu hooks needed to prepare gmem-allocated
pages before mapping them into guest private memory ranges
This includes basic support for attestation guest requests, enough
to say that KVM supports the GHCB 2.0 specification
There is no support yet for loading into the firmware those signing
keys to be used for attestation requests, and therefore no need yet
for the host to provide certificate data for those keys.
To support fetching certificate data from userspace, a new KVM exit
type will be needed to handle fetching the certificate from
userspace.
An attempt to define a new KVM_EXIT_COCO / KVM_EXIT_COCO_REQ_CERTS
exit type to handle this was introduced in v1 of this patchset, but
is still being discussed by community, so for now this patchset
only implements a stub version of SNP Extended Guest Requests that
does not provide certificate data
x86 - Intel:
- Remove an unnecessary EPT TLB flush when enabling hardware
- Fix a series of bugs that cause KVM to fail to detect nested
pending posted interrupts as valid wake eents for a vCPU executing
HLT in L2 (with HLT-exiting disable by L1)
- KVM: x86: Suppress MMIO that is triggered during task switch
emulation
Explicitly suppress userspace emulated MMIO exits that are
triggered when emulating a task switch as KVM doesn't support
userspace MMIO during complex (multi-step) emulation
Silently ignoring the exit request can result in the
WARN_ON_ONCE(vcpu->mmio_needed) firing if KVM exits to userspace
for some other reason prior to purging mmio_needed
See commit 0dc902267cb3 ("KVM: x86: Suppress pending MMIO write
exits if emulator detects exception") for more details on KVM's
limitations with respect to emulated MMIO during complex emulator
flows
Generic:
- Rename the AS_UNMOVABLE flag that was introduced for KVM to
AS_INACCESSIBLE, because the special casing needed by these pages
is not due to just unmovability (and in fact they are only
unmovable because the CPU cannot access them)
- New ioctl to populate the KVM page tables in advance, which is
useful to mitigate KVM page faults during guest boot or after live
migration. The code will also be used by TDX, but (probably) not
through the ioctl
- Enable halt poll shrinking by default, as Intel found it to be a
clear win
- Setup empty IRQ routing when creating a VM to avoid having to
synchronize SRCU when creating a split IRQCHIP on x86
- Rework the sched_in/out() paths to replace kvm_arch_sched_in() with
a flag that arch code can use for hooking both sched_in() and
sched_out()
- Take the vCPU @id as an "unsigned long" instead of "u32" to avoid
truncating a bogus value from userspace, e.g. to help userspace
detect bugs
- Mark a vCPU as preempted if and only if it's scheduled out while in
the KVM_RUN loop, e.g. to avoid marking it preempted and thus
writing guest memory when retrieving guest state during live
migration blackout
Selftests:
- Remove dead code in the memslot modification stress test
- Treat "branch instructions retired" as supported on all AMD Family
17h+ CPUs
- Print the guest pseudo-RNG seed only when it changes, to avoid
spamming the log for tests that create lots of VMs
- Make the PMU counters test less flaky when counting LLC cache
misses by doing CLFLUSH{OPT} in every loop iteration"
* tag 'for-linus' of git://git.kernel.org/pub/scm/virt/kvm/kvm: (227 commits)
crypto: ccp: Add the SNP_VLEK_LOAD command
KVM: x86/pmu: Add kvm_pmu_call() to simplify static calls of kvm_pmu_ops
KVM: x86: Introduce kvm_x86_call() to simplify static calls of kvm_x86_ops
KVM: x86: Replace static_call_cond() with static_call()
KVM: SEV: Provide support for SNP_EXTENDED_GUEST_REQUEST NAE event
x86/sev: Move sev_guest.h into common SEV header
KVM: SEV: Provide support for SNP_GUEST_REQUEST NAE event
KVM: x86: Suppress MMIO that is triggered during task switch emulation
KVM: x86/mmu: Clean up make_huge_page_split_spte() definition and intro
KVM: x86/mmu: Bug the VM if KVM tries to split a !hugepage SPTE
KVM: selftests: x86: Add test for KVM_PRE_FAULT_MEMORY
KVM: x86: Implement kvm_arch_vcpu_pre_fault_memory()
KVM: x86/mmu: Make kvm_mmu_do_page_fault() return mapped level
KVM: x86/mmu: Account pf_{fixed,emulate,spurious} in callers of "do page fault"
KVM: x86/mmu: Bump pf_taken stat only in the "real" page fault handler
KVM: Add KVM_PRE_FAULT_MEMORY vcpu ioctl to pre-populate guest memory
KVM: Document KVM_PRE_FAULT_MEMORY ioctl
mm, virt: merge AS_UNMOVABLE and AS_INACCESSIBLE
perf kvm: Add kvm-stat for loongarch64
LoongArch: KVM: Add PV steal time support in guest side
...
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KVM x86 MTRR virtualization removal
Remove support for virtualizing MTRRs on Intel CPUs, along with a nasty CR0.CD
hack, and instead always honor guest PAT on CPUs that support self-snoop.
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Drop KVM's emulation of CR0.CD=1 on Intel CPUs now that KVM no longer
honors guest MTRR memtypes, as forcing UC memory for VMs with
non-coherent DMA only makes sense if the guest is using something other
than PAT to configure the memtype for the DMA region.
Furthermore, KVM has forced WB memory for CR0.CD=1 since commit
fb279950ba02 ("KVM: vmx: obey KVM_QUIRK_CD_NW_CLEARED"), and no known
VMM in existence disables KVM_X86_QUIRK_CD_NW_CLEARED, let alone does
so with non-coherent DMA.
Lastly, commit fb279950ba02 ("KVM: vmx: obey KVM_QUIRK_CD_NW_CLEARED") was
from the same author as commit b18d5431acc7 ("KVM: x86: fix CR0.CD
virtualization"), and followed by a mere month. I.e. forcing UC memory
was likely the result of code inspection or perhaps misdiagnosed failures,
and not the necessitate by a concrete use case.
Update KVM's documentation to note that KVM_X86_QUIRK_CD_NW_CLEARED is now
AMD-only, and to take an erratum for lack of CR0.CD virtualization on
Intel.
Tested-by: Xiangfei Ma <xiangfeix.ma@intel.com>
Tested-by: Yongwei Ma <yongwei.ma@intel.com>
Link: https://lore.kernel.org/r/20240309010929.1403984-3-seanjc@google.com
Signed-off-by: Sean Christopherson <seanjc@google.com>
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Remove KVM's support for virtualizing guest MTRR memtypes, as full MTRR
adds no value, negatively impacts guest performance, and is a maintenance
burden due to it's complexity and oddities.
KVM's approach to virtualizating MTRRs make no sense, at all. KVM *only*
honors guest MTRR memtypes if EPT is enabled *and* the guest has a device
that may perform non-coherent DMA access. From a hardware virtualization
perspective of guest MTRRs, there is _nothing_ special about EPT. Legacy
shadowing paging doesn't magically account for guest MTRRs, nor does NPT.
Unwinding and deciphering KVM's murky history, the MTRR virtualization
code appears to be the result of misdiagnosed issues when EPT + VT-d with
passthrough devices was enabled years and years ago. And importantly, the
underlying bugs that were fudged around by honoring guest MTRR memtypes
have since been fixed (though rather poorly in some cases).
The zapping GFNs logic in the MTRR virtualization code came from:
commit efdfe536d8c643391e19d5726b072f82964bfbdb
Author: Xiao Guangrong <guangrong.xiao@linux.intel.com>
Date: Wed May 13 14:42:27 2015 +0800
KVM: MMU: fix MTRR update
Currently, whenever guest MTRR registers are changed
kvm_mmu_reset_context is called to switch to the new root shadow page
table, however, it's useless since:
1) the cache type is not cached into shadow page's attribute so that
the original root shadow page will be reused
2) the cache type is set on the last spte, that means we should sync
the last sptes when MTRR is changed
This patch fixs this issue by drop all the spte in the gfn range which
is being updated by MTRR
which was a fix for:
commit 0bed3b568b68e5835ef5da888a372b9beabf7544
Author: Sheng Yang <sheng@linux.intel.com>
AuthorDate: Thu Oct 9 16:01:54 2008 +0800
Commit: Avi Kivity <avi@redhat.com>
CommitDate: Wed Dec 31 16:51:44 2008 +0200
KVM: Improve MTRR structure
As well as reset mmu context when set MTRR.
which was part of a "MTRR/PAT support for EPT" series that also added:
+ if (mt_mask) {
+ mt_mask = get_memory_type(vcpu, gfn) <<
+ kvm_x86_ops->get_mt_mask_shift();
+ spte |= mt_mask;
+ }
where get_memory_type() was a truly gnarly helper to retrieve the guest
MTRR memtype for a given memtype. And *very* subtly, at the time of that
change, KVM *always* set VMX_EPT_IGMT_BIT,
kvm_mmu_set_base_ptes(VMX_EPT_READABLE_MASK |
VMX_EPT_WRITABLE_MASK |
VMX_EPT_DEFAULT_MT << VMX_EPT_MT_EPTE_SHIFT |
VMX_EPT_IGMT_BIT);
which came in via:
commit 928d4bf747e9c290b690ff515d8f81e8ee226d97
Author: Sheng Yang <sheng@linux.intel.com>
AuthorDate: Thu Nov 6 14:55:45 2008 +0800
Commit: Avi Kivity <avi@redhat.com>
CommitDate: Tue Nov 11 21:00:37 2008 +0200
KVM: VMX: Set IGMT bit in EPT entry
There is a potential issue that, when guest using pagetable without vmexit when
EPT enabled, guest would use PAT/PCD/PWT bits to index PAT msr for it's memory,
which would be inconsistent with host side and would cause host MCE due to
inconsistent cache attribute.
The patch set IGMT bit in EPT entry to ignore guest PAT and use WB as default
memory type to protect host (notice that all memory mapped by KVM should be WB).
Note the CommitDates! The AuthorDates strongly suggests Sheng Yang added
the whole "ignoreIGMT things as a bug fix for issues that were detected
during EPT + VT-d + passthrough enabling, but it was applied earlier
because it was a generic fix.
Jumping back to 0bed3b568b68 ("KVM: Improve MTRR structure"), the other
relevant code, or rather lack thereof, is the handling of *host* MMIO.
That fix came in a bit later, but given the author and timing, it's safe
to say it was all part of the same EPT+VT-d enabling mess.
commit 2aaf69dcee864f4fb6402638dd2f263324ac839f
Author: Sheng Yang <sheng@linux.intel.com>
AuthorDate: Wed Jan 21 16:52:16 2009 +0800
Commit: Avi Kivity <avi@redhat.com>
CommitDate: Sun Feb 15 02:47:37 2009 +0200
KVM: MMU: Map device MMIO as UC in EPT
Software are not allow to access device MMIO using cacheable memory type, the
patch limit MMIO region with UC and WC(guest can select WC using PAT and
PCD/PWT).
In addition to the host MMIO and IGMT issues, KVM's MTRR virtualization
was obviously never tested on NPT until much later, which lends further
credence to the theory/argument that this was all the result of
misdiagnosed issues.
Discussion from the EPT+MTRR enabling thread[*] more or less confirms that
Sheng Yang was trying to resolve issues with passthrough MMIO.
* Sheng Yang
: Do you mean host(qemu) would access this memory and if we set it to guest
: MTRR, host access would be broken? We would cover this in our shadow MTRR
: patch, for we encountered this in video ram when doing some experiment with
: VGA assignment.
And in the same thread, there's also what appears to be confirmation of
Intel running into issues with Windows XP related to a guest device driver
mapping DMA with WC in the PAT.
* Avi Kavity
: Sheng Yang wrote:
: > Yes... But it's easy to do with assigned devices' mmio, but what if guest
: > specific some non-mmio memory's memory type? E.g. we have met one issue in
: > Xen, that a assigned-device's XP driver specific one memory region as buffer,
: > and modify the memory type then do DMA.
: >
: > Only map MMIO space can be first step, but I guess we can modify assigned
: > memory region memory type follow guest's?
: >
:
: With ept/npt, we can't, since the memory type is in the guest's
: pagetable entries, and these are not accessible.
[*] https://lore.kernel.org/all/1223539317-32379-1-git-send-email-sheng@linux.intel.com
So, for the most part, what likely happened is that 15 years ago, a few
engineers (a) fixed a #MC problem by ignoring guest PAT and (b) initially
"fixed" passthrough device MMIO by emulating *guest* MTRRs. Except for
the below case, everything since then has been a result of those two
intertwined changes.
The one exception, which is actually yet more confirmation of all of the
above, is the revert of Paolo's attempt at "full" virtualization of guest
MTRRs:
commit 606decd67049217684e3cb5a54104d51ddd4ef35
Author: Paolo Bonzini <pbonzini@redhat.com>
Date: Thu Oct 1 13:12:47 2015 +0200
Revert "KVM: x86: apply guest MTRR virtualization on host reserved pages"
This reverts commit fd717f11015f673487ffc826e59b2bad69d20fe5.
It was reported to cause Machine Check Exceptions (bug 104091).
...
commit fd717f11015f673487ffc826e59b2bad69d20fe5
Author: Paolo Bonzini <pbonzini@redhat.com>
Date: Tue Jul 7 14:38:13 2015 +0200
KVM: x86: apply guest MTRR virtualization on host reserved pages
Currently guest MTRR is avoided if kvm_is_reserved_pfn returns true.
However, the guest could prefer a different page type than UC for
such pages. A good example is that pass-throughed VGA frame buffer is
not always UC as host expected.
This patch enables full use of virtual guest MTRRs.
I.e. Paolo tried to add back KVM's behavior before "Map device MMIO as UC
in EPT" and got the same result: machine checks, likely due to the guest
MTRRs not being trustworthy/sane at all times.
Note, Paolo also tried to enable MTRR virtualization on SVM+NPT, but that
too got reverted. Unfortunately, it doesn't appear that anyone ever found
a smoking gun, i.e. exactly why emulating guest MTRRs via NPT PAT caused
extremely slow boot times doesn't appear to have a definitive root cause.
commit fc07e76ac7ffa3afd621a1c3858a503386a14281
Author: Paolo Bonzini <pbonzini@redhat.com>
Date: Thu Oct 1 13:20:22 2015 +0200
Revert "KVM: SVM: use NPT page attributes"
This reverts commit 3c2e7f7de3240216042b61073803b61b9b3cfb22.
Initializing the mapping from MTRR to PAT values was reported to
fail nondeterministically, and it also caused extremely slow boot
(due to caching getting disabled---bug 103321) with assigned devices.
...
commit 3c2e7f7de3240216042b61073803b61b9b3cfb22
Author: Paolo Bonzini <pbonzini@redhat.com>
Date: Tue Jul 7 14:32:17 2015 +0200
KVM: SVM: use NPT page attributes
Right now, NPT page attributes are not used, and the final page
attribute depends solely on gPAT (which however is not synced
correctly), the guest MTRRs and the guest page attributes.
However, we can do better by mimicking what is done for VMX.
In the absence of PCI passthrough, the guest PAT can be ignored
and the page attributes can be just WB. If passthrough is being
used, instead, keep respecting the guest PAT, and emulate the guest
MTRRs through the PAT field of the nested page tables.
The only snag is that WP memory cannot be emulated correctly,
because Linux's default PAT setting only includes the other types.
In short, honoring guest MTRRs for VMX was initially a workaround of
sorts for KVM ignoring guest PAT *and* for KVM not forcing UC for host
MMIO. And while there *are* known cases where honoring guest MTRRs is
desirable, e.g. passthrough VGA frame buffers, the desired behavior in
that case is to get WC instead of UC, i.e. at this point it's for
performance, not correctness.
Furthermore, the complete absence of MTRR virtualization on NPT and
shadow paging proves that, while KVM theoretically can do better, it's
by no means necessary for correctnesss.
Lastly, since kernels mostly rely on firmware to do MTRR setup, and the
host typically provides guest firmware, honoring guest MTRRs is effectively
honoring *host* userspace memtypes, which is also backwards. I.e. it
would be far better for host userspace to communicate its desired memtype
directly to KVM (or perhaps indirectly via VMAs in the host kernel), not
through guest MTRRs.
Tested-by: Xiangfei Ma <xiangfeix.ma@intel.com>
Tested-by: Yongwei Ma <yongwei.ma@intel.com>
Link: https://lore.kernel.org/r/20240309010929.1403984-2-seanjc@google.com
Signed-off-by: Sean Christopherson <seanjc@google.com>
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KVM x86 misc changes for 6.11
- Add a global struct to consolidate tracking of host values, e.g. EFER, and
move "shadow_phys_bits" into the structure as "maxphyaddr".
- Add KVM_CAP_X86_APIC_BUS_CYCLES_NS to allow configuring the effective APIC
bus frequency, because TDX.
- Print the name of the APICv/AVIC inhibits in the relevant tracepoint.
- Clean up KVM's handling of vendor specific emulation to consistently act on
"compatible with Intel/AMD", versus checking for a specific vendor.
- Misc cleanups
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When a vCPU is interrupted by a signal while running a nested guest,
KVM will exit to userspace with L2 state. However, userspace has no
way to know whether it sees L1 or L2 state (besides calling
KVM_GET_STATS_FD, which does not have a stable ABI).
This causes multiple problems:
The simplest one is L2 state corruption when userspace marks the sregs
as dirty. See this mailing list thread [1] for a complete discussion.
Another problem is that if userspace decides to continue by emulating
instructions, it will unknowingly emulate with L2 state as if L1
doesn't exist, which can be considered a weird guest escape.
Introduce a new flag, KVM_RUN_X86_GUEST_MODE, in the kvm_run data
structure, which is set when the vCPU exited while running a nested
guest. Also introduce a new capability, KVM_CAP_X86_GUEST_MODE, to
advertise the functionality to userspace.
[1] https://lore.kernel.org/kvm/20240416123558.212040-1-julian.stecklina@cyberus-technology.de/T/#m280aadcb2e10ae02c191a7dc4ed4b711a74b1f55
Signed-off-by: Thomas Prescher <thomas.prescher@cyberus-technology.de>
Signed-off-by: Julian Stecklina <julian.stecklina@cyberus-technology.de>
Link: https://lore.kernel.org/r/20240508132502.184428-1-julian.stecklina@cyberus-technology.de
Signed-off-by: Sean Christopherson <seanjc@google.com>
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Improve the description for the KVM_CAP_X86_BUS_LOCK_EXIT capability to
fix a few typos and grammar issues, and to clarify the purpose of the
capability.
Signed-off-by: Carlos López <clopez@suse.de>
Link: https://lore.kernel.org/r/20240424105616.29596-1-clopez@suse.de
[sean: massage changelog]
Signed-off-by: Sean Christopherson <seanjc@google.com>
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Add KVM_CAP_X86_APIC_BUS_CYCLES_NS capability to configure the APIC
bus clock frequency for APIC timer emulation.
Allow KVM_ENABLE_CAPABILITY(KVM_CAP_X86_APIC_BUS_CYCLES_NS) to set the
frequency in nanoseconds. When using this capability, the user space
VMM should configure CPUID leaf 0x15 to advertise the frequency.
Vishal reported that the TDX guest kernel expects a 25MHz APIC bus
frequency but ends up getting interrupts at a significantly higher rate.
The TDX architecture hard-codes the core crystal clock frequency to
25MHz and mandates exposing it via CPUID leaf 0x15. The TDX architecture
does not allow the VMM to override the value.
In addition, per Intel SDM:
"The APIC timer frequency will be the processor’s bus clock or core
crystal clock frequency (when TSC/core crystal clock ratio is
enumerated in CPUID leaf 0x15) divided by the value specified in
the divide configuration register."
The resulting 25MHz APIC bus frequency conflicts with the KVM hardcoded
APIC bus frequency of 1GHz.
The KVM doesn't enumerate CPUID leaf 0x15 to the guest unless the user
space VMM sets it using KVM_SET_CPUID. If the CPUID leaf 0x15 is
enumerated, the guest kernel uses it as the APIC bus frequency. If not,
the guest kernel measures the frequency based on other known timers like
the ACPI timer or the legacy PIT. As reported by Vishal the TDX guest
kernel expects a 25MHz timer frequency but gets timer interrupt more
frequently due to the 1GHz frequency used by KVM.
To ensure that the guest doesn't have a conflicting view of the APIC bus
frequency, allow the userspace to tell KVM to use the same frequency that
TDX mandates instead of the default 1Ghz.
Reported-by: Vishal Annapurve <vannapurve@google.com>
Closes: https://lore.kernel.org/lkml/20231006011255.4163884-1-vannapurve@google.com
Signed-off-by: Isaku Yamahata <isaku.yamahata@intel.com>
Reviewed-by: Rick Edgecombe <rick.p.edgecombe@intel.com>
Co-developed-by: Reinette Chatre <reinette.chatre@intel.com>
Signed-off-by: Reinette Chatre <reinette.chatre@intel.com>
Reviewed-by: Xiaoyao Li <xiaoyao.li@intel.com>
Reviewed-by: Yuan Yao <yuan.yao@intel.com>
Link: https://lore.kernel.org/r/6748a4c12269e756f0c48680da8ccc5367c31ce7.1714081726.git.reinette.chatre@intel.com
Signed-off-by: Sean Christopherson <seanjc@google.com>
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KVM generic changes for 6.11
- Enable halt poll shrinking by default, as Intel found it to be a clear win.
- Setup empty IRQ routing when creating a VM to avoid having to synchronize
SRCU when creating a split IRQCHIP on x86.
- Rework the sched_in/out() paths to replace kvm_arch_sched_in() with a flag
that arch code can use for hooking both sched_in() and sched_out().
- Take the vCPU @id as an "unsigned long" instead of "u32" to avoid
truncating a bogus value from userspace, e.g. to help userspace detect bugs.
- Mark a vCPU as preempted if and only if it's scheduled out while in the
KVM_RUN loop, e.g. to avoid marking it preempted and thus writing guest
memory when retrieving guest state during live migration blackout.
- A few minor cleanups
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The documentation for KVM_CAP_VM_MOVE_ENC_CONTEXT_FROM doesn't use the
correct keyword formatting, which breaks rendering on
https://www.kernel.org/doc/html/latest/virt/kvm/api.html.
Signed-off-by: Julian Stecklina <julian.stecklina@cyberus-technology.de>
Link: https://lore.kernel.org/r/20240520143220.340737-1-julian.stecklina@cyberus-technology.de
Signed-off-by: Sean Christopherson <seanjc@google.com>
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Update KVM's halt-polling documentation to correclty reflect that KVM has
4 relevant module params, not 3 params.
Co-developed-by: Rajendran Jaishankar <jaishankar.rajendran@intel.com>
Signed-off-by: Rajendran Jaishankar <jaishankar.rajendran@intel.com>
Signed-off-by: Parshuram Sangle <parshuram.sangle@intel.com>
Link: https://lore.kernel.org/r/20231102154628.2120-3-parshuram.sangle@intel.com
[sean: drop unrelated and misleading doc update]
Signed-off-by: Sean Christopherson <seanjc@google.com>
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Default halt_poll_ns_shrink value of 0 always resets polling interval
to 0 on an un-successful poll where vcpu wakeup is not received. This is
mostly to avoid pointless polling for more number of shorter intervals. But
disabled shrink assumes vcpu wakeup is less likely to be received in
subsequent shorter polling intervals. Another side effect of 0 shrink value
is that, even on a successful poll if total block time was greater than
current polling interval, the polling interval starts over from 0 instead
of shrinking by a factor.
Enabling shrink with value of 2 allows the polling interval to gradually
decrement in case of un-successful poll events as well. This gives a fair
chance for successful polling events in subsequent polling intervals rather
than resetting it to 0 and starting over from grow_start.
Below kvm stat log snippet shows interleaved growth and shrinking of
polling interval:
87162647182125: kvm_halt_poll_ns: vcpu 0: halt_poll_ns 10000 (grow 0)
87162647637763: kvm_halt_poll_ns: vcpu 0: halt_poll_ns 20000 (grow 10000)
87162649627943: kvm_halt_poll_ns: vcpu 0: halt_poll_ns 40000 (grow 20000)
87162650892407: kvm_halt_poll_ns: vcpu 0: halt_poll_ns 20000 (shrink 40000)
87162651540378: kvm_halt_poll_ns: vcpu 0: halt_poll_ns 40000 (grow 20000)
87162652276768: kvm_halt_poll_ns: vcpu 0: halt_poll_ns 20000 (shrink 40000)
87162652515037: kvm_halt_poll_ns: vcpu 0: halt_poll_ns 40000 (grow 20000)
87162653383787: kvm_halt_poll_ns: vcpu 0: halt_poll_ns 20000 (shrink 40000)
87162653627670: kvm_halt_poll_ns: vcpu 0: halt_poll_ns 10000 (shrink 20000)
87162653796321: kvm_halt_poll_ns: vcpu 0: halt_poll_ns 20000 (grow 10000)
87162656171645: kvm_halt_poll_ns: vcpu 0: halt_poll_ns 10000 (shrink 20000)
87162661607487: kvm_halt_poll_ns: vcpu 0: halt_poll_ns 0 (shrink 10000)
Having both grow and shrink enabled creates a balance in polling interval
growth and shrink behavior. Tests show improved successful polling attempt
ratio which contribute to VM performance. Power penalty is quite negligible
as shrunk polling intervals create bursts of very short durations.
Performance assessment results show 3-6% improvements in CPU+GPU, Memory
and Storage Android VM workloads whereas 5-9% improvement in average FPS of
gaming VM workloads.
Power penalty is below 1% where host OS is either idle or running a
native workload having 2 VMs enabled. CPU/GPU intensive gaming workloads
as well do not show any increased power overhead with shrink enabled.
Co-developed-by: Rajendran Jaishankar <jaishankar.rajendran@intel.com>
Signed-off-by: Rajendran Jaishankar <jaishankar.rajendran@intel.com>
Signed-off-by: Parshuram Sangle <parshuram.sangle@intel.com>
Link: https://lore.kernel.org/r/20231102154628.2120-2-parshuram.sangle@intel.com
Signed-off-by: Sean Christopherson <seanjc@google.com>
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git://git.kernel.org/pub/scm/linux/kernel/git/kvmarm/kvmarm into HEAD
KVM/arm64 changes for 6.11
- Initial infrastructure for shadow stage-2 MMUs, as part of nested
virtualization enablement
- Support for userspace changes to the guest CTR_EL0 value, enabling
(in part) migration of VMs between heterogenous hardware
- Fixes + improvements to pKVM's FF-A proxy, adding support for v1.1 of
the protocol
- FPSIMD/SVE support for nested, including merged trap configuration
and exception routing
- New command-line parameter to control the WFx trap behavior under KVM
- Introduce kCFI hardening in the EL2 hypervisor
- Fixes + cleanups for handling presence/absence of FEAT_TCRX
- Miscellaneous fixes + documentation updates
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In arch/arm64/include/uapi/asm/kvm.h, we have
#define KVM_VGIC_V2_CPU_SIZE 0x2000
So the CPU interface address space should cover 8 KByte not 4 KByte.
Signed-off-by: Changyuan Lyu <changyuanl@google.com>
Link: https://lore.kernel.org/r/20240623164542.2999626-3-changyuanl@google.com
Signed-off-by: Oliver Upton <oliver.upton@linux.dev>
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The expression `irq_type[n]` may confuse readers to interpret `n`
as the bit position and think of CPU = 1 << 0, SPI = 1 << 1, and
PPI = 1 << 2.
Since arch/arm64/include/uapi/asm/kvm.h already has macro definitions
for the allowed values, this commit uses these symbols to clear up
the ambiguity.
Signed-off-by: Changyuan Lyu <changyuanl@google.com>
Link: https://lore.kernel.org/r/20240623164542.2999626-2-changyuanl@google.com
Signed-off-by: Oliver Upton <oliver.upton@linux.dev>
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BDF is the acronym for Bus, Device, Function.
Signed-off-by: Changyuan Lyu <changyuanl@google.com>
Link: https://lore.kernel.org/r/20240623164542.2999626-1-changyuanl@google.com
Signed-off-by: Oliver Upton <oliver.upton@linux.dev>
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https://git.kernel.org/pub/scm/linux/kernel/git/kvms390/linux into HEAD
Assortment of tiny fixes which are not time critical:
- Rejecting memory region operations for ucontrol mode VMs
- Rewind the PSW on host intercepts for VSIE
- Remove unneeded include
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This change rejects the KVM_SET_USER_MEMORY_REGION and
KVM_SET_USER_MEMORY_REGION2 ioctls when called on a ucontrol VM.
This is necessary since ucontrol VMs have kvm->arch.gmap set to 0 and
would thus result in a null pointer dereference further in.
Memory management needs to be performed in userspace and using the
ioctls KVM_S390_UCAS_MAP and KVM_S390_UCAS_UNMAP.
Also improve s390 specific documentation for KVM_SET_USER_MEMORY_REGION
and KVM_SET_USER_MEMORY_REGION2.
Signed-off-by: Christoph Schlameuss <schlameuss@linux.ibm.com>
Fixes: 27e0393f15fc ("KVM: s390: ucontrol: per vcpu address spaces")
Reviewed-by: Claudio Imbrenda <imbrenda@linux.ibm.com>
Link: https://lore.kernel.org/r/20240624095902.29375-1-schlameuss@linux.ibm.com
Signed-off-by: Janosch Frank <frankja@linux.ibm.com>
[frankja@linux.ibm.com: commit message spelling fix, subject prefix fix]
Message-ID: <20240624095902.29375-1-schlameuss@linux.ibm.com>
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Adds documentation of KVM_PRE_FAULT_MEMORY ioctl. [1]
It populates guest memory. It doesn't do extra operations on the
underlying technology-specific initialization [2]. For example,
CoCo-related operations won't be performed. Concretely for TDX, this API
won't invoke TDH.MEM.PAGE.ADD() or TDH.MR.EXTEND(). Vendor-specific APIs
are required for such operations.
The key point is to adapt of vcpu ioctl instead of VM ioctl. First,
populating guest memory requires vcpu. If it is VM ioctl, we need to pick
one vcpu somehow. Secondly, vcpu ioctl allows each vcpu to invoke this
ioctl in parallel. It helps to scale regarding guest memory size, e.g.,
hundreds of GB.
[1] https://lore.kernel.org/kvm/Zbrj5WKVgMsUFDtb@google.com/
[2] https://lore.kernel.org/kvm/Ze-TJh0BBOWm9spT@google.com/
Suggested-by: Sean Christopherson <seanjc@google.com>
Signed-off-by: Isaku Yamahata <isaku.yamahata@intel.com>
Message-ID: <9a060293c9ad9a78f1d8994cfe1311e818e99257.1712785629.git.isaku.yamahata@intel.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
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Pull base x86 KVM support for running SEV-SNP guests from Michael Roth:
* add some basic infrastructure and introduces a new KVM_X86_SNP_VM
vm_type to handle differences versus the existing KVM_X86_SEV_VM and
KVM_X86_SEV_ES_VM types.
* implement the KVM API to handle the creation of a cryptographic
launch context, encrypt/measure the initial image into guest memory,
and finalize it before launching it.
* implement handling for various guest-generated events such as page
state changes, onlining of additional vCPUs, etc.
* implement the gmem/mmu hooks needed to prepare gmem-allocated pages
before mapping them into guest private memory ranges as well as
cleaning them up prior to returning them to the host for use as
normal memory. Because those cleanup hooks supplant certain
activities like issuing WBINVDs during KVM MMU invalidations, avoid
duplicating that work to avoid unecessary overhead.
This merge leaves out support support for attestation guest requests
and for loading the signing keys to be used for attestation requests.
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Add a KVM_SEV_SNP_LAUNCH_FINISH command to finalize the cryptographic
launch digest which stores the measurement of the guest at launch time.
Also extend the existing SNP firmware data structures to support
disabling the use of Versioned Chip Endorsement Keys (VCEK) by guests as
part of this command.
While finalizing the launch flow, the code also issues the LAUNCH_UPDATE
SNP firmware commands to encrypt/measure the initial VMSA pages for each
configured vCPU, which requires setting the RMP entries for those pages
to private, so also add handling to clean up the RMP entries for these
pages whening freeing vCPUs during shutdown.
Signed-off-by: Brijesh Singh <brijesh.singh@amd.com>
Co-developed-by: Michael Roth <michael.roth@amd.com>
Signed-off-by: Michael Roth <michael.roth@amd.com>
Signed-off-by: Harald Hoyer <harald@profian.com>
Signed-off-by: Ashish Kalra <ashish.kalra@amd.com>
Message-ID: <20240501085210.2213060-8-michael.roth@amd.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
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A key aspect of a launching an SNP guest is initializing it with a
known/measured payload which is then encrypted into guest memory as
pre-validated private pages and then measured into the cryptographic
launch context created with KVM_SEV_SNP_LAUNCH_START so that the guest
can attest itself after booting.
Since all private pages are provided by guest_memfd, make use of the
kvm_gmem_populate() interface to handle this. The general flow is that
guest_memfd will handle allocating the pages associated with the GPA
ranges being initialized by each particular call of
KVM_SEV_SNP_LAUNCH_UPDATE, copying data from userspace into those pages,
and then the post_populate callback will do the work of setting the
RMP entries for these pages to private and issuing the SNP firmware
calls to encrypt/measure them.
For more information see the SEV-SNP specification.
Signed-off-by: Brijesh Singh <brijesh.singh@amd.com>
Co-developed-by: Michael Roth <michael.roth@amd.com>
Signed-off-by: Michael Roth <michael.roth@amd.com>
Signed-off-by: Ashish Kalra <ashish.kalra@amd.com>
Message-ID: <20240501085210.2213060-7-michael.roth@amd.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
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KVM_SEV_SNP_LAUNCH_START begins the launch process for an SEV-SNP guest.
The command initializes a cryptographic digest context used to construct
the measurement of the guest. Other commands can then at that point be
used to load/encrypt data into the guest's initial launch image.
For more information see the SEV-SNP specification.
Signed-off-by: Brijesh Singh <brijesh.singh@amd.com>
Co-developed-by: Michael Roth <michael.roth@amd.com>
Signed-off-by: Michael Roth <michael.roth@amd.com>
Signed-off-by: Ashish Kalra <ashish.kalra@amd.com>
Message-ID: <20240501085210.2213060-6-michael.roth@amd.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
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The patch adds a one-reg register identifier which can be used to
read and set the virtual HASHPKEYR for the guest during enter/exit
with KVM_REG_PPC_HASHPKEYR. The specific SPR KVM API documentation
too updated.
Signed-off-by: Shivaprasad G Bhat <sbhat@linux.ibm.com>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Link: https://msgid.link/171759285547.1480.12374595786792346073.stgit@linux.ibm.com
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The patch adds a one-reg register identifier which can be used to
read and set the virtual HASHKEYR for the guest during enter/exit
with KVM_REG_PPC_HASHKEYR. The specific SPR KVM API documentation
too updated.
Signed-off-by: Shivaprasad G Bhat <sbhat@linux.ibm.com>
Reviewed-by: Nicholas Piggin <npiggin@gmail.com>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Link: https://msgid.link/171759283170.1480.12904332463112769129.stgit@linux.ibm.com
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The patch adds a one-reg register identifier which can be used to
read and set the DEXCR for the guest during enter/exit with
KVM_REG_PPC_DEXCR. The specific SPR KVM API documentation
too updated.
Signed-off-by: Shivaprasad G Bhat <sbhat@linux.ibm.com>
Reviewed-by: Nicholas Piggin <npiggin@gmail.com>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Link: https://msgid.link/171759279613.1480.12873911783530175699.stgit@linux.ibm.com
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git://git.kernel.org/pub/scm/linux/kernel/git/powerpc/linux
Pull powerpc updates from Michael Ellerman:
- Enable BPF Kernel Functions (kfuncs) in the powerpc BPF JIT.
- Allow per-process DEXCR (Dynamic Execution Control Register) settings
via prctl, notably NPHIE which controls hashst/hashchk for ROP
protection.
- Install powerpc selftests in sub-directories. Note this changes the
way run_kselftest.sh needs to be invoked for powerpc selftests.
- Change fadump (Firmware Assisted Dump) to better handle memory
add/remove.
- Add support for passing additional parameters to the fadump kernel.
- Add support for updating the kdump image on CPU/memory add/remove
events.
- Other small features, cleanups and fixes.
Thanks to Andrew Donnellan, Andy Shevchenko, Aneesh Kumar K.V, Arnd
Bergmann, Benjamin Gray, Bjorn Helgaas, Christian Zigotzky, Christophe
Jaillet, Christophe Leroy, Colin Ian King, Cédric Le Goater, Dr. David
Alan Gilbert, Erhard Furtner, Frank Li, GUO Zihua, Ganesh Goudar, Geoff
Levand, Ghanshyam Agrawal, Greg Kurz, Hari Bathini, Joel Stanley, Justin
Stitt, Kunwu Chan, Li Yang, Lidong Zhong, Madhavan Srinivasan, Mahesh
Salgaonkar, Masahiro Yamada, Matthias Schiffer, Naresh Kamboju, Nathan
Chancellor, Nathan Lynch, Naveen N Rao, Nicholas Miehlbradt, Ran Wang,
Randy Dunlap, Ritesh Harjani, Sachin Sant, Shirisha Ganta, Shrikanth
Hegde, Sourabh Jain, Stephen Rothwell, sundar, Thorsten Blum, Vaibhav
Jain, Xiaowei Bao, Yang Li, and Zhao Chenhui.
* tag 'powerpc-6.10-1' of git://git.kernel.org/pub/scm/linux/kernel/git/powerpc/linux: (85 commits)
powerpc/fadump: Fix section mismatch warning
powerpc/85xx: fix compile error without CONFIG_CRASH_DUMP
powerpc/fadump: update documentation about bootargs_append
powerpc/fadump: pass additional parameters when fadump is active
powerpc/fadump: setup additional parameters for dump capture kernel
powerpc/pseries/fadump: add support for multiple boot memory regions
selftests/powerpc/dexcr: Fix spelling mistake "predicition" -> "prediction"
KVM: PPC: Book3S HV nestedv2: Fix an error handling path in gs_msg_ops_kvmhv_nestedv2_config_fill_info()
KVM: PPC: Fix documentation for ppc mmu caps
KVM: PPC: code cleanup for kvmppc_book3s_irqprio_deliver
KVM: PPC: Book3S HV nestedv2: Cancel pending DEC exception
powerpc/xmon: Check cpu id in commands "c#", "dp#" and "dx#"
powerpc/code-patching: Use dedicated memory routines for patching
powerpc/code-patching: Test patch_instructions() during boot
powerpc64/kasan: Pass virtual addresses to kasan_init_phys_region()
powerpc: rename SPRN_HID2 define to SPRN_HID2_750FX
powerpc: Fix typos
powerpc/eeh: Fix spelling of the word "auxillary" and update comment
macintosh/ams: Fix unused variable warning
powerpc/Makefile: Remove bits related to the previous use of -mcmodel=large
...
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The documentation mentions KVM_CAP_PPC_RADIX_MMU, but the defines in the
kvm headers spell it KVM_CAP_PPC_MMU_RADIX. Similarly with
KVM_CAP_PPC_MMU_HASH_V3.
Fixes: c92701322711 ("KVM: PPC: Book3S HV: Add userspace interfaces for POWER9 MMU")
Signed-off-by: Joel Stanley <joel@jms.id.au>
Acked-by: Paul Mackerras <paulus@ozlabs.org>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Link: https://msgid.link/20230411061446.26324-1-joel@jms.id.au
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KVM cleanups for 6.10:
- Misc cleanups extracted from the "exit on missing userspace mapping" series,
which has been put on hold in anticipation of a "KVM Userfault" approach,
which should provide a superset of functionality.
- Remove kvm_make_all_cpus_request_except(), which got added to hack around an
AVIC bug, and then became dead code when a more robust fix came along.
- Fix a goof in the KVM_CREATE_GUEST_MEMFD documentation.
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The KVM_CREATE_GUEST_MEMFD ioctl returns a file descriptor, and is
documented as such in the description. However, the "Returns" field
in the documentation states that the ioctl returns 0 on success.
Update this to match the description.
Signed-off-by: Carlos López <clopez@suse.de>
Fixes: a7800aa80ea4 ("KVM: Add KVM_CREATE_GUEST_MEMFD ioctl() for guest-specific backing memory")
Link: https://lore.kernel.org/r/20240424103317.28522-1-clopez@suse.de
Signed-off-by: Sean Christopherson <seanjc@google.com>
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