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// SPDX-License-Identifier: GPL-2.0-only
/*
* Kernel-based Virtual Machine driver for Linux
*
* Macros and functions to access KVM PTEs (also known as SPTEs)
*
* Copyright (C) 2006 Qumranet, Inc.
* Copyright 2020 Red Hat, Inc. and/or its affiliates.
*/
#define pr_fmt(fmt) KBUILD_MODNAME ": " fmt
#include <linux/kvm_host.h>
#include "mmu.h"
#include "mmu_internal.h"
#include "x86.h"
#include "spte.h"
#include <asm/e820/api.h>
#include <asm/memtype.h>
#include <asm/vmx.h>
bool __read_mostly enable_mmio_caching = true;
static bool __ro_after_init allow_mmio_caching;
module_param_named(mmio_caching, enable_mmio_caching, bool, 0444);
EXPORT_SYMBOL_GPL(enable_mmio_caching);
u64 __read_mostly shadow_host_writable_mask;
u64 __read_mostly shadow_mmu_writable_mask;
u64 __read_mostly shadow_nx_mask;
u64 __read_mostly shadow_x_mask; /* mutual exclusive with nx_mask */
u64 __read_mostly shadow_user_mask;
u64 __read_mostly shadow_accessed_mask;
u64 __read_mostly shadow_dirty_mask;
u64 __read_mostly shadow_mmio_value;
u64 __read_mostly shadow_mmio_mask;
u64 __read_mostly shadow_mmio_access_mask;
u64 __read_mostly shadow_present_mask;
u64 __read_mostly shadow_memtype_mask;
u64 __read_mostly shadow_me_value;
u64 __read_mostly shadow_me_mask;
u64 __read_mostly shadow_acc_track_mask;
u64 __read_mostly shadow_nonpresent_or_rsvd_mask;
u64 __read_mostly shadow_nonpresent_or_rsvd_lower_gfn_mask;
u8 __read_mostly shadow_phys_bits;
void __init kvm_mmu_spte_module_init(void)
{
/*
* Snapshot userspace's desire to allow MMIO caching. Whether or not
* KVM can actually enable MMIO caching depends on vendor-specific
* hardware capabilities and other module params that can't be resolved
* until the vendor module is loaded, i.e. enable_mmio_caching can and
* will change when the vendor module is (re)loaded.
*/
allow_mmio_caching = enable_mmio_caching;
}
static u64 generation_mmio_spte_mask(u64 gen)
{
u64 mask;
WARN_ON_ONCE(gen & ~MMIO_SPTE_GEN_MASK);
mask = (gen << MMIO_SPTE_GEN_LOW_SHIFT) & MMIO_SPTE_GEN_LOW_MASK;
mask |= (gen << MMIO_SPTE_GEN_HIGH_SHIFT) & MMIO_SPTE_GEN_HIGH_MASK;
return mask;
}
u64 make_mmio_spte(struct kvm_vcpu *vcpu, u64 gfn, unsigned int access)
{
u64 gen = kvm_vcpu_memslots(vcpu)->generation & MMIO_SPTE_GEN_MASK;
u64 spte = generation_mmio_spte_mask(gen);
u64 gpa = gfn << PAGE_SHIFT;
WARN_ON_ONCE(!vcpu->kvm->arch.shadow_mmio_value);
access &= shadow_mmio_access_mask;
spte |= vcpu->kvm->arch.shadow_mmio_value | access;
spte |= gpa | shadow_nonpresent_or_rsvd_mask;
spte |= (gpa & shadow_nonpresent_or_rsvd_mask)
<< SHADOW_NONPRESENT_OR_RSVD_MASK_LEN;
return spte;
}
static bool kvm_is_mmio_pfn(kvm_pfn_t pfn)
{
if (pfn_valid(pfn))
return !is_zero_pfn(pfn) && PageReserved(pfn_to_page(pfn)) &&
/*
* Some reserved pages, such as those from NVDIMM
* DAX devices, are not for MMIO, and can be mapped
* with cached memory type for better performance.
* However, the above check misconceives those pages
* as MMIO, and results in KVM mapping them with UC
* memory type, which would hurt the performance.
* Therefore, we check the host memory type in addition
* and only treat UC/UC-/WC pages as MMIO.
*/
(!pat_enabled() || pat_pfn_immune_to_uc_mtrr(pfn));
return !e820__mapped_raw_any(pfn_to_hpa(pfn),
pfn_to_hpa(pfn + 1) - 1,
E820_TYPE_RAM);
}
/*
* Returns true if the SPTE has bits that may be set without holding mmu_lock.
* The caller is responsible for checking if the SPTE is shadow-present, and
* for determining whether or not the caller cares about non-leaf SPTEs.
*/
bool spte_has_volatile_bits(u64 spte)
{
/*
* Always atomically update spte if it can be updated
* out of mmu-lock, it can ensure dirty bit is not lost,
* also, it can help us to get a stable is_writable_pte()
* to ensure tlb flush is not missed.
*/
if (!is_writable_pte(spte) && is_mmu_writable_spte(spte))
return true;
if (is_access_track_spte(spte))
return true;
if (spte_ad_enabled(spte)) {
if (!(spte & shadow_accessed_mask) ||
(is_writable_pte(spte) && !(spte & shadow_dirty_mask)))
return true;
}
return false;
}
bool make_spte(struct kvm_vcpu *vcpu, struct kvm_mmu_page *sp,
const struct kvm_memory_slot *slot,
unsigned int pte_access, gfn_t gfn, kvm_pfn_t pfn,
u64 old_spte, bool prefetch, bool can_unsync,
bool host_writable, u64 *new_spte)
{
int level = sp->role.level;
u64 spte = SPTE_MMU_PRESENT_MASK;
bool wrprot = false;
/*
* For the EPT case, shadow_present_mask has no RWX bits set if
* exec-only page table entries are supported. In that case,
* ACC_USER_MASK and shadow_user_mask are used to represent
* read access. See FNAME(gpte_access) in paging_tmpl.h.
*/
WARN_ON_ONCE((pte_access | shadow_present_mask) == SHADOW_NONPRESENT_VALUE);
if (sp->role.ad_disabled)
spte |= SPTE_TDP_AD_DISABLED;
else if (kvm_mmu_page_ad_need_write_protect(sp))
spte |= SPTE_TDP_AD_WRPROT_ONLY;
spte |= shadow_present_mask;
if (!prefetch)
spte |= spte_shadow_accessed_mask(spte);
/*
* For simplicity, enforce the NX huge page mitigation even if not
* strictly necessary. KVM could ignore the mitigation if paging is
* disabled in the guest, as the guest doesn't have any page tables to
* abuse. But to safely ignore the mitigation, KVM would have to
* ensure a new MMU is loaded (or all shadow pages zapped) when CR0.PG
* is toggled on, and that's a net negative for performance when TDP is
* enabled. When TDP is disabled, KVM will always switch to a new MMU
* when CR0.PG is toggled, but leveraging that to ignore the mitigation
* would tie make_spte() further to vCPU/MMU state, and add complexity
* just to optimize a mode that is anything but performance critical.
*/
if (level > PG_LEVEL_4K && (pte_access & ACC_EXEC_MASK) &&
is_nx_huge_page_enabled(vcpu->kvm)) {
pte_access &= ~ACC_EXEC_MASK;
}
if (pte_access & ACC_EXEC_MASK)
spte |= shadow_x_mask;
else
spte |= shadow_nx_mask;
if (pte_access & ACC_USER_MASK)
spte |= shadow_user_mask;
if (level > PG_LEVEL_4K)
spte |= PT_PAGE_SIZE_MASK;
if (shadow_memtype_mask)
spte |= static_call(kvm_x86_get_mt_mask)(vcpu, gfn,
kvm_is_mmio_pfn(pfn));
if (host_writable)
spte |= shadow_host_writable_mask;
else
pte_access &= ~ACC_WRITE_MASK;
if (shadow_me_value && !kvm_is_mmio_pfn(pfn))
spte |= shadow_me_value;
spte |= (u64)pfn << PAGE_SHIFT;
if (pte_access & ACC_WRITE_MASK) {
spte |= PT_WRITABLE_MASK | shadow_mmu_writable_mask;
/*
* Optimization: for pte sync, if spte was writable the hash
* lookup is unnecessary (and expensive). Write protection
* is responsibility of kvm_mmu_get_page / kvm_mmu_sync_roots.
* Same reasoning can be applied to dirty page accounting.
*/
if (is_writable_pte(old_spte))
goto out;
/*
* Unsync shadow pages that are reachable by the new, writable
* SPTE. Write-protect the SPTE if the page can't be unsync'd,
* e.g. it's write-tracked (upper-level SPs) or has one or more
* shadow pages and unsync'ing pages is not allowed.
*/
if (mmu_try_to_unsync_pages(vcpu->kvm, slot, gfn, can_unsync, prefetch)) {
wrprot = true;
pte_access &= ~ACC_WRITE_MASK;
spte &= ~(PT_WRITABLE_MASK | shadow_mmu_writable_mask);
}
}
if (pte_access & ACC_WRITE_MASK)
spte |= spte_shadow_dirty_mask(spte);
out:
if (prefetch)
spte = mark_spte_for_access_track(spte);
WARN_ONCE(is_rsvd_spte(&vcpu->arch.mmu->shadow_zero_check, spte, level),
"spte = 0x%llx, level = %d, rsvd bits = 0x%llx", spte, level,
get_rsvd_bits(&vcpu->arch.mmu->shadow_zero_check, spte, level));
if ((spte & PT_WRITABLE_MASK) && kvm_slot_dirty_track_enabled(slot)) {
/* Enforced by kvm_mmu_hugepage_adjust. */
WARN_ON_ONCE(level > PG_LEVEL_4K);
mark_page_dirty_in_slot(vcpu->kvm, slot, gfn);
}
*new_spte = spte;
return wrprot;
}
static u64 make_spte_executable(u64 spte)
{
bool is_access_track = is_access_track_spte(spte);
if (is_access_track)
spte = restore_acc_track_spte(spte);
spte &= ~shadow_nx_mask;
spte |= shadow_x_mask;
if (is_access_track)
spte = mark_spte_for_access_track(spte);
return spte;
}
/*
* Construct an SPTE that maps a sub-page of the given huge page SPTE where
* `index` identifies which sub-page.
*
* This is used during huge page splitting to build the SPTEs that make up the
* new page table.
*/
u64 make_huge_page_split_spte(struct kvm *kvm, u64 huge_spte, union kvm_mmu_page_role role,
int index)
{
u64 child_spte;
if (WARN_ON_ONCE(!is_shadow_present_pte(huge_spte)))
return 0;
if (WARN_ON_ONCE(!is_large_pte(huge_spte)))
return 0;
child_spte = huge_spte;
/*
* The child_spte already has the base address of the huge page being
* split. So we just have to OR in the offset to the page at the next
* lower level for the given index.
*/
child_spte |= (index * KVM_PAGES_PER_HPAGE(role.level)) << PAGE_SHIFT;
if (role.level == PG_LEVEL_4K) {
child_spte &= ~PT_PAGE_SIZE_MASK;
/*
* When splitting to a 4K page where execution is allowed, mark
* the page executable as the NX hugepage mitigation no longer
* applies.
*/
if ((role.access & ACC_EXEC_MASK) && is_nx_huge_page_enabled(kvm))
child_spte = make_spte_executable(child_spte);
}
return child_spte;
}
u64 make_nonleaf_spte(u64 *child_pt, bool ad_disabled)
{
u64 spte = SPTE_MMU_PRESENT_MASK;
spte |= __pa(child_pt) | shadow_present_mask | PT_WRITABLE_MASK |
shadow_user_mask | shadow_x_mask | shadow_me_value;
if (ad_disabled)
spte |= SPTE_TDP_AD_DISABLED;
else
spte |= shadow_accessed_mask;
return spte;
}
u64 mark_spte_for_access_track(u64 spte)
{
if (spte_ad_enabled(spte))
return spte & ~shadow_accessed_mask;
if (is_access_track_spte(spte))
return spte;
check_spte_writable_invariants(spte);
WARN_ONCE(spte & (SHADOW_ACC_TRACK_SAVED_BITS_MASK <<
SHADOW_ACC_TRACK_SAVED_BITS_SHIFT),
"Access Tracking saved bit locations are not zero\n");
spte |= (spte & SHADOW_ACC_TRACK_SAVED_BITS_MASK) <<
SHADOW_ACC_TRACK_SAVED_BITS_SHIFT;
spte &= ~shadow_acc_track_mask;
return spte;
}
void kvm_mmu_set_mmio_spte_mask(u64 mmio_value, u64 mmio_mask, u64 access_mask)
{
BUG_ON((u64)(unsigned)access_mask != access_mask);
WARN_ON(mmio_value & shadow_nonpresent_or_rsvd_lower_gfn_mask);
/*
* Reset to the original module param value to honor userspace's desire
* to (dis)allow MMIO caching. Update the param itself so that
* userspace can see whether or not KVM is actually using MMIO caching.
*/
enable_mmio_caching = allow_mmio_caching;
if (!enable_mmio_caching)
mmio_value = 0;
/*
* The mask must contain only bits that are carved out specifically for
* the MMIO SPTE mask, e.g. to ensure there's no overlap with the MMIO
* generation.
*/
if (WARN_ON(mmio_mask & ~SPTE_MMIO_ALLOWED_MASK))
mmio_value = 0;
/*
* Disable MMIO caching if the MMIO value collides with the bits that
* are used to hold the relocated GFN when the L1TF mitigation is
* enabled. This should never fire as there is no known hardware that
* can trigger this condition, e.g. SME/SEV CPUs that require a custom
* MMIO value are not susceptible to L1TF.
*/
if (WARN_ON(mmio_value & (shadow_nonpresent_or_rsvd_mask <<
SHADOW_NONPRESENT_OR_RSVD_MASK_LEN)))
mmio_value = 0;
/*
* The masked MMIO value must obviously match itself and a removed SPTE
* must not get a false positive. Removed SPTEs and MMIO SPTEs should
* never collide as MMIO must set some RWX bits, and removed SPTEs must
* not set any RWX bits.
*/
if (WARN_ON((mmio_value & mmio_mask) != mmio_value) ||
WARN_ON(mmio_value && (FROZEN_SPTE & mmio_mask) == mmio_value))
mmio_value = 0;
if (!mmio_value)
enable_mmio_caching = false;
shadow_mmio_value = mmio_value;
shadow_mmio_mask = mmio_mask;
shadow_mmio_access_mask = access_mask;
}
EXPORT_SYMBOL_GPL(kvm_mmu_set_mmio_spte_mask);
void kvm_mmu_set_me_spte_mask(u64 me_value, u64 me_mask)
{
/* shadow_me_value must be a subset of shadow_me_mask */
if (WARN_ON(me_value & ~me_mask))
me_value = me_mask = 0;
shadow_me_value = me_value;
shadow_me_mask = me_mask;
}
EXPORT_SYMBOL_GPL(kvm_mmu_set_me_spte_mask);
void kvm_mmu_set_ept_masks(bool has_ad_bits, bool has_exec_only)
{
shadow_user_mask = VMX_EPT_READABLE_MASK;
shadow_accessed_mask = has_ad_bits ? VMX_EPT_ACCESS_BIT : 0ull;
shadow_dirty_mask = has_ad_bits ? VMX_EPT_DIRTY_BIT : 0ull;
shadow_nx_mask = 0ull;
shadow_x_mask = VMX_EPT_EXECUTABLE_MASK;
/* VMX_EPT_SUPPRESS_VE_BIT is needed for W or X violation. */
shadow_present_mask =
(has_exec_only ? 0ull : VMX_EPT_READABLE_MASK) | VMX_EPT_SUPPRESS_VE_BIT;
/*
* EPT overrides the host MTRRs, and so KVM must program the desired
* memtype directly into the SPTEs. Note, this mask is just the mask
* of all bits that factor into the memtype, the actual memtype must be
* dynamically calculated, e.g. to ensure host MMIO is mapped UC.
*/
shadow_memtype_mask = VMX_EPT_MT_MASK | VMX_EPT_IPAT_BIT;
shadow_acc_track_mask = VMX_EPT_RWX_MASK;
shadow_host_writable_mask = EPT_SPTE_HOST_WRITABLE;
shadow_mmu_writable_mask = EPT_SPTE_MMU_WRITABLE;
/*
* EPT Misconfigurations are generated if the value of bits 2:0
* of an EPT paging-structure entry is 110b (write/execute).
*/
kvm_mmu_set_mmio_spte_mask(VMX_EPT_MISCONFIG_WX_VALUE,
VMX_EPT_RWX_MASK | VMX_EPT_SUPPRESS_VE_BIT, 0);
}
EXPORT_SYMBOL_GPL(kvm_mmu_set_ept_masks);
void kvm_mmu_reset_all_pte_masks(void)
{
u8 low_phys_bits;
u64 mask;
shadow_phys_bits = kvm_get_shadow_phys_bits();
/*
* If the CPU has 46 or less physical address bits, then set an
* appropriate mask to guard against L1TF attacks. Otherwise, it is
* assumed that the CPU is not vulnerable to L1TF.
*
* Some Intel CPUs address the L1 cache using more PA bits than are
* reported by CPUID. Use the PA width of the L1 cache when possible
* to achieve more effective mitigation, e.g. if system RAM overlaps
* the most significant bits of legal physical address space.
*/
shadow_nonpresent_or_rsvd_mask = 0;
low_phys_bits = boot_cpu_data.x86_phys_bits;
if (boot_cpu_has_bug(X86_BUG_L1TF) &&
!WARN_ON_ONCE(boot_cpu_data.x86_cache_bits >=
52 - SHADOW_NONPRESENT_OR_RSVD_MASK_LEN)) {
low_phys_bits = boot_cpu_data.x86_cache_bits
- SHADOW_NONPRESENT_OR_RSVD_MASK_LEN;
shadow_nonpresent_or_rsvd_mask =
rsvd_bits(low_phys_bits, boot_cpu_data.x86_cache_bits - 1);
}
shadow_nonpresent_or_rsvd_lower_gfn_mask =
GENMASK_ULL(low_phys_bits - 1, PAGE_SHIFT);
shadow_user_mask = PT_USER_MASK;
shadow_accessed_mask = PT_ACCESSED_MASK;
shadow_dirty_mask = PT_DIRTY_MASK;
shadow_nx_mask = PT64_NX_MASK;
shadow_x_mask = 0;
shadow_present_mask = PT_PRESENT_MASK;
/*
* For shadow paging and NPT, KVM uses PAT entry '0' to encode WB
* memtype in the SPTEs, i.e. relies on host MTRRs to provide the
* correct memtype (WB is the "weakest" memtype).
*/
shadow_memtype_mask = 0;
shadow_acc_track_mask = 0;
shadow_me_mask = 0;
shadow_me_value = 0;
shadow_host_writable_mask = DEFAULT_SPTE_HOST_WRITABLE;
shadow_mmu_writable_mask = DEFAULT_SPTE_MMU_WRITABLE;
/*
* Set a reserved PA bit in MMIO SPTEs to generate page faults with
* PFEC.RSVD=1 on MMIO accesses. 64-bit PTEs (PAE, x86-64, and EPT
* paging) support a maximum of 52 bits of PA, i.e. if the CPU supports
* 52-bit physical addresses then there are no reserved PA bits in the
* PTEs and so the reserved PA approach must be disabled.
*/
if (shadow_phys_bits < 52)
mask = BIT_ULL(51) | PT_PRESENT_MASK;
else
mask = 0;
kvm_mmu_set_mmio_spte_mask(mask, mask, ACC_WRITE_MASK | ACC_USER_MASK);
}
|