KVM: x86/mmu: Check for present SPTE when clearing dirty bit in TDP MMU

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@google.com>
Signed-off-by: Sean Christopherson <seanjc@google.com>
Reviewed-by: Ben Gardon <bgardon@google.com>
Message-Id: <20220226001546.360188-3-seanjc@google.com>
Cc: stable@vger.kernel.org
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

diff --git a/arch/x86/kvm/mmu/tdp_mmu.c b/arch/x86/kvm/mmu/tdp_mmu.c
index aabb1a908fbc5b0e44963e140ac2dd6ffd200cad..853780eb033b4a4d8bd1123440efe1ca8e606a62 100644 (file)
--- 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))
                        continue;
 
+               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;