[PATCH 5.15 773/913] KVM: x86/mmu: Check for present SPTE when clearing dirty bit in TDP MMU

From: Greg Kroah-Hartman
Date: Tue Apr 05 2022 - 17:10:04 EST

From: Sean Christopherson <seanjc@xxxxxxxxxx>

commit 3354ef5a592d219364cf442c2f784ce7ad7629fd upstream.

Explicitly check for present SPTEs when clearing dirty bits in the TDP
MMU. This isn't strictly required for correctness, as setting the dirty
bit in a defunct SPTE will not change the SPTE from !PRESENT to PRESENT.
However, the guarded MMU_WARN_ON() in spte_ad_need_write_protect() would
complain if anyone actually turned on KVM's MMU debugging.

Fixes: a6a0b05da9f3 ("kvm: x86/mmu: Support dirty logging for the TDP MMU")
Cc: Ben Gardon <bgardon@xxxxxxxxxx>
Signed-off-by: Sean Christopherson <seanjc@xxxxxxxxxx>
Reviewed-by: Ben Gardon <bgardon@xxxxxxxxxx>
Message-Id: <20220226001546.360188-3-seanjc@xxxxxxxxxx>
Cc: stable@xxxxxxxxxxxxxxx
Signed-off-by: Paolo Bonzini <pbonzini@xxxxxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
arch/x86/kvm/mmu/tdp_mmu.c | 3 +++
1 file changed, 3 insertions(+)

--- a/arch/x86/kvm/mmu/tdp_mmu.c
+++ b/arch/x86/kvm/mmu/tdp_mmu.c
@@ -1316,6 +1316,9 @@ retry:
if (tdp_mmu_iter_cond_resched(kvm, &iter, false, true))

+ if (!is_shadow_present_pte(iter.old_spte))
+ continue;
if (spte_ad_need_write_protect(iter.old_spte)) {
if (is_writable_pte(iter.old_spte))
new_spte = iter.old_spte & ~PT_WRITABLE_MASK;