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    Subject[PATCH 5.16 0861/1017] KVM: x86/mmu: Check for present SPTE when clearing dirty bit in TDP MMU
    Date
    From: Sean Christopherson <seanjc@google.com>

    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>
    ---
    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
    @@ -1261,6 +1261,9 @@ 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;

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