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KVM: x86/mmu: Always update A/D-disabled SPTEs atomically

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In anticipation of aging SPTEs outside of mmu_lock, force A/D-disabled
SPTEs to be updated atomically, as aging A/D-disabled SPTEs will mark them
for access-tracking outside of mmu_lock.  Coupled with restoring access-
tracked SPTEs in the fast page fault handler, the end result is that
A/D-disable SPTEs will be volatile at all times.

Reviewed-by: James Houghton <jthoughton@google.com>
Link: https://lore.kernel.org/all/Z60bhK96JnKIgqZQ@google.com
Signed-off-by: Sean Christopherson <seanjc@google.com>
This commit is contained in:
Sean Christopherson 2025-02-12 12:58:39 -08:00
parent 61d65f2dc7
commit 928c54b1c4
1 changed files with 6 additions and 4 deletions
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10
arch/x86/kvm/mmu/spte.c
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@ -141,8 +141,11 @@ bool spte_needs_atomic_update(u64 spte)
if (!is_writable_pte(spte) && is_mmu_writable_spte(spte))
return true;
/* Access-tracked SPTEs can be restored by KVM's fast page fault handler. */
if (is_access_track_spte(spte))
/*
* A/D-disabled SPTEs can be access-tracked by aging, and access-tracked
* SPTEs can be restored by KVM's fast page fault handler.
*/
if (!spte_ad_enabled(spte))
return true;
/*
@ -151,8 +154,7 @@ bool spte_needs_atomic_update(u64 spte)
* invalidate TLBs when aging SPTEs, and so it's safe to clobber the
* Accessed bit (and rare in practice).
*/
return spte_ad_enabled(spte) && is_writable_pte(spte) &&
!(spte & shadow_dirty_mask);
return is_writable_pte(spte) && !(spte & shadow_dirty_mask);
}
bool make_spte(struct kvm_vcpu *vcpu, struct kvm_mmu_page *sp,