linux-kernel - [PATCH v2 05/30] KVM: x86/mmu: Check for present SPTE when clearing dirty bit in TDP MMU

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Message-Id: <20211223222318.1039223-6-seanjc@google.com>
Date:   Thu, 23 Dec 2021 22:22:53 +0000
From:   Sean Christopherson <seanjc@...gle.com>
To:     Paolo Bonzini <pbonzini@...hat.com>
Cc:     Sean Christopherson <seanjc@...gle.com>,
        Vitaly Kuznetsov <vkuznets@...hat.com>,
        Wanpeng Li <wanpengli@...cent.com>,
        Jim Mattson <jmattson@...gle.com>,
        Joerg Roedel <joro@...tes.org>, kvm@...r.kernel.org,
        linux-kernel@...r.kernel.org, Ben Gardon <bgardon@...gle.com>,
        David Matlack <dmatlack@...gle.com>,
        Mingwei Zhang <mizhang@...gle.com>
Subject: [PATCH v2 05/30] KVM: x86/mmu: Check for present SPTE when clearing
 dirty bit in TDP MMU

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@...gle.com>
Signed-off-by: Sean Christopherson <seanjc@...gle.com>
Reviewed-by: Ben Gardon <bgardon@...gle.com>
---
 arch/x86/kvm/mmu/tdp_mmu.c | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/arch/x86/kvm/mmu/tdp_mmu.c b/arch/x86/kvm/mmu/tdp_mmu.c
index 41e975841ea6..fcbae282af6f 100644
--- a/arch/x86/kvm/mmu/tdp_mmu.c
+++ b/arch/x86/kvm/mmu/tdp_mmu.c
@@ -1239,6 +1239,9 @@ static bool clear_dirty_gfn_range(struct kvm *kvm, struct kvm_mmu_page *root,
 		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;
-- 
2.34.1.448.ga2b2bfdf31-goog