mirrors/linux
2
0
Fork 0
mirror of https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git synced 2026-05-10 13:59:45 -04:00
Code Issues Packages Projects Releases Wiki Activity

KVM: x86/mmu: Locally cache whether a PFN is host MMIO when making a SPTE

Browse Source 
When making a SPTE, cache whether or not the target PFN is host MMIO in
order to avoid multiple rounds of the slow path of kvm_is_mmio_pfn(), e.g.
hitting pat_pfn_immune_to_uc_mtrr() in particular can be problematic.  KVM
currently avoids multiple calls by virtue of the two users being mutually
exclusive (.get_mt_mask() is Intel-only, shadow_me_value is AMD-only), but
that won't hold true if/when KVM needs to detect host MMIO mappings for
other reasons, e.g. for mitigating the MMIO Stale Data vulnerability.

No functional change intended.

Tested-by: Pawan Gupta <pawan.kumar.gupta@linux.intel.com>
Link: https://lore.kernel.org/r/20250523011756.3243624-3-seanjc@google.com
Signed-off-by: Sean Christopherson <seanjc@google.com>
This commit is contained in:
Sean Christopherson
2025-05-22 18:17:53 -07:00
parent c126b46e6f
commit ffe9d7966d
1 changed files with 18 additions and 4 deletions
Download Patch File Download Diff File Expand all files Collapse all files

22
arch/x86/kvm/mmu/spte.c
View File

@@ -104,7 +104,7 @@ u64 make_mmio_spte(struct kvm_vcpu *vcpu, u64 gfn, unsigned int access)
return spte;
}
static bool kvm_is_mmio_pfn(kvm_pfn_t pfn)
static bool __kvm_is_mmio_pfn(kvm_pfn_t pfn)
{
if (pfn_valid(pfn))
return !is_zero_pfn(pfn) && PageReserved(pfn_to_page(pfn)) &&
@@ -125,6 +125,19 @@ static bool kvm_is_mmio_pfn(kvm_pfn_t pfn)
E820_TYPE_RAM);
}
static bool kvm_is_mmio_pfn(kvm_pfn_t pfn, int *is_host_mmio)
{
/*
* Determining if a PFN is host MMIO is relative expensive. Cache the
* result locally (in the sole caller) to avoid doing the full query
* multiple times when creating a single SPTE.
*/
if (*is_host_mmio < 0)
*is_host_mmio = __kvm_is_mmio_pfn(pfn);
return *is_host_mmio;
}
/*
* Returns true if the SPTE needs to be updated atomically due to having bits
* that may be changed without holding mmu_lock, and for which KVM must not
@@ -162,6 +175,7 @@ bool make_spte(struct kvm_vcpu *vcpu, struct kvm_mmu_page *sp,
{
int level = sp->role.level;
u64 spte = SPTE_MMU_PRESENT_MASK;
int is_host_mmio = -1;
bool wrprot = false;
/*
@@ -210,14 +224,14 @@ bool make_spte(struct kvm_vcpu *vcpu, struct kvm_mmu_page *sp,
spte |= PT_PAGE_SIZE_MASK;
if (kvm_x86_ops.get_mt_mask)
spte |= kvm_x86_call(get_mt_mask)(vcpu, gfn, kvm_is_mmio_pfn(pfn));
spte |= kvm_x86_call(get_mt_mask)(vcpu, gfn,
kvm_is_mmio_pfn(pfn, &is_host_mmio));
if (host_writable)
spte |= shadow_host_writable_mask;
else
pte_access &= ~ACC_WRITE_MASK;
if (shadow_me_value && !kvm_is_mmio_pfn(pfn))
if (shadow_me_value && !kvm_is_mmio_pfn(pfn, &is_host_mmio))
spte |= shadow_me_value;
spte |= (u64)pfn << PAGE_SHIFT;