[PATCH 16/18] KVM: x86/mmu: Set Dirty bit for new SPTEs, even if _hardware_ A/D bits are disabled

Sean Christopherson
2024-10-11T02:11:27Z

When making a SPTE, set the Dirty bit in the SPTE as appropriate, even if
hardware A/D bits are disabled. Only EPT allows A/D bits to be disabled,
and for EPT, the bits are software-available (ignored by hardware) when
A/D bits are disabled, i.e. it is perfectly legal for KVM to use the Dirty
to track dirty pages in software.

Signed-off-by: Sean Christopherson <seanjc@google.com>
---
arch/x86/kvm/mmu/spte.c | 2 +-
arch/x86/kvm/mmu/spte.h | 6 ------
2 files changed, 1 insertion(+), 7 deletions(-)

diff --git a/arch/x86/kvm/mmu/spte.c b/arch/x86/kvm/mmu/spte.c
index 617479efd127..fd8c3c92ade0 100644
--- a/arch/x86/kvm/mmu/spte.c
+++ b/arch/x86/kvm/mmu/spte.c
@@ -237,7 +237,7 @@ bool make_spte(struct kvm_vcpu *vcpu, struct kvm_mmu_page *sp,
wrprot = true;
else
spte |= PT_WRITABLE_MASK | shadow_mmu_writable_mask |
- spte_shadow_dirty_mask(spte);
+ shadow_dirty_mask;
}

if (prefetch && !synchronizing)
diff --git a/arch/x86/kvm/mmu/spte.h b/arch/x86/kvm/mmu/spte.h
index a404279ba731..e90cc401c168 100644
--- a/arch/x86/kvm/mmu/spte.h
+++ b/arch/x86/kvm/mmu/spte.h
@@ -316,12 +316,6 @@ static inline bool spte_ad_need_write_protect(u64 spte)
return (spte & SPTE_TDP_AD_MASK) != SPTE_TDP_AD_ENABLED;
}

-static inline u64 spte_shadow_dirty_mask(u64 spte)
-{
- KVM_MMU_WARN_ON(!is_shadow_present_pte(spte));
- return spte_ad_enabled(spte) ? shadow_dirty_mask : 0;
-}
-
static inline bool is_access_track_spte(u64 spte)
{
return !spte_ad_enabled(spte) && (spte & shadow_acc_track_mask) == 0;
--
2.47.0.rc1.288.g06298d1525-goog