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

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.

Link: https://lore.kernel.org/r/20241011021051.1557902-17-seanjc@google.com
Signed-off-by: Sean Christopherson <seanjc@google.com>

Author: sean-jc

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)

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;