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From:   isaku.yamahata@intel.com
To:     kvm@vger.kernel.org, linux-kernel@vger.kernel.org
Cc:     isaku.yamahata@intel.com, isaku.yamahata@gmail.com,
        Paolo Bonzini <pbonzini@redhat.com>,
        Jim Mattson <jmattson@google.com>, erdemaktas@google.com,
        Connor Kuehl <ckuehl@redhat.com>,
        Sean Christopherson <seanjc@google.com>
Subject: [RFC PATCH v5 036/104] KVM: x86/mmu: Explicitly check for MMIO spte in fast page fault
Date:   Fri,  4 Mar 2022 11:48:52 -0800
Message-Id: <b0e81b4a4abfbe8bd6d43e4b1c0349a79517dfb0.1646422845.git.isaku.yamahata@intel.com>
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From: Sean Christopherson <sean.j.christopherson@intel.com>

Explicitly check for an MMIO spte in the fast page fault flow.  TDX will
use a not-present entry for MMIO sptes, which can be mistaken for an
access-tracked spte since both have SPTE_SPECIAL_MASK set.

The fast page fault handles the case of changing access bits without
obtaining mmu_lock.  For example, clear write protect bit for dirty page
tracking.  MMIO emulation is handled in a slow path.  So it doesn't affect
the default VM case.

Signed-off-by: Sean Christopherson <sean.j.christopherson@intel.com>
Signed-off-by: Isaku Yamahata <isaku.yamahata@intel.com>
---
 arch/x86/kvm/mmu/mmu.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/arch/x86/kvm/mmu/mmu.c b/arch/x86/kvm/mmu/mmu.c
index b68191aa39bf..9907cb759fd1 100644
--- a/arch/x86/kvm/mmu/mmu.c
+++ b/arch/x86/kvm/mmu/mmu.c
@@ -3167,7 +3167,7 @@ static int fast_page_fault(struct kvm_vcpu *vcpu, struct kvm_page_fault *fault)
 			break;
 
 		sp = sptep_to_sp(sptep);
-		if (!is_last_spte(spte, sp->role.level))
+		if (!is_last_spte(spte, sp->role.level) || is_mmio_spte(spte))
 			break;
 
 		/*
-- 
2.25.1