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| author | Paolo Bonzini <pbonzini@redhat.com> | 2024-07-16 15:54:57 +0200 |
|---|---|---|
| committer | Paolo Bonzini <pbonzini@redhat.com> | 2024-07-16 15:54:57 +0200 |
| commit | 5c5ddf71071f01fabe9380e16c36c9263d40d528 (patch) | |
| tree | b7693fc445cc7df841414f6ed6387f651d0b66f5 /Documentation/virt | |
| parent | Merge tag 'kvm-x86-mmu-6.11' of https://github.com/kvm-x86/linux into HEAD (diff) | |
| parent | KVM: VMX: Always honor guest PAT on CPUs that support self-snoop (diff) | |
| download | linux-5c5ddf71071f01fabe9380e16c36c9263d40d528.tar.xz linux-5c5ddf71071f01fabe9380e16c36c9263d40d528.zip | |
Merge tag 'kvm-x86-mtrrs-6.11' of https://github.com/kvm-x86/linux into HEAD
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.
Diffstat (limited to 'Documentation/virt')
| -rw-r--r-- | Documentation/virt/kvm/api.rst | 6 | ||||
| -rw-r--r-- | Documentation/virt/kvm/x86/errata.rst | 18 |
2 files changed, 23 insertions, 1 deletions
diff --git a/Documentation/virt/kvm/api.rst b/Documentation/virt/kvm/api.rst index 798ad65f4fee..8e5dad80b337 100644 --- a/Documentation/virt/kvm/api.rst +++ b/Documentation/virt/kvm/api.rst @@ -8025,7 +8025,11 @@ The valid bits in cap.args[0] are: When this quirk is disabled, the reset value is 0x10000 (APIC_LVT_MASKED). - KVM_X86_QUIRK_CD_NW_CLEARED By default, KVM clears CR0.CD and CR0.NW. + KVM_X86_QUIRK_CD_NW_CLEARED By default, KVM clears CR0.CD and CR0.NW on + AMD CPUs to workaround buggy guest firmware + that runs in perpetuity with CR0.CD, i.e. + with caches in "no fill" mode. + When this quirk is disabled, KVM does not change the value of CR0.CD and CR0.NW. diff --git a/Documentation/virt/kvm/x86/errata.rst b/Documentation/virt/kvm/x86/errata.rst index 49a05f24747b..4116045a8744 100644 --- a/Documentation/virt/kvm/x86/errata.rst +++ b/Documentation/virt/kvm/x86/errata.rst @@ -48,3 +48,21 @@ have the same physical APIC ID, KVM will deliver events targeting that APIC ID only to the vCPU with the lowest vCPU ID. If KVM_X2APIC_API_USE_32BIT_IDS is not enabled, KVM follows x86 architecture when processing interrupts (all vCPUs matching the target APIC ID receive the interrupt). + +MTRRs +----- +KVM does not virtualize guest MTRR memory types. KVM emulates accesses to MTRR +MSRs, i.e. {RD,WR}MSR in the guest will behave as expected, but KVM does not +honor guest MTRRs when determining the effective memory type, and instead +treats all of guest memory as having Writeback (WB) MTRRs. + +CR0.CD +------ +KVM does not virtualize CR0.CD on Intel CPUs. Similar to MTRR MSRs, KVM +emulates CR0.CD accesses so that loads and stores from/to CR0 behave as +expected, but setting CR0.CD=1 has no impact on the cachaeability of guest +memory. + +Note, this erratum does not affect AMD CPUs, which fully virtualize CR0.CD in +hardware, i.e. put the CPU caches into "no fill" mode when CR0.CD=1, even when +running in the guest.
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