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Reply-To: Sean Christopherson <seanjc@google.com>
Date:   Sat, 26 Feb 2022 00:15:41 +0000
In-Reply-To: <20220226001546.360188-1-seanjc@google.com>
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Subject: [PATCH v3 23/28] KVM: x86/mmu: Check for a REMOVED leaf SPTE before
 making the SPTE
From:   Sean Christopherson <seanjc@google.com>
To:     Paolo Bonzini <pbonzini@redhat.com>,
        Christian Borntraeger <borntraeger@linux.ibm.com>,
        Janosch Frank <frankja@linux.ibm.com>,
        Claudio Imbrenda <imbrenda@linux.ibm.com>
Cc:     Sean Christopherson <seanjc@google.com>,
        Vitaly Kuznetsov <vkuznets@redhat.com>,
        Wanpeng Li <wanpengli@tencent.com>,
        Jim Mattson <jmattson@google.com>,
        Joerg Roedel <joro@8bytes.org>,
        David Hildenbrand <david@redhat.com>, kvm@vger.kernel.org,
        linux-kernel@vger.kernel.org, David Matlack <dmatlack@google.com>,
        Ben Gardon <bgardon@google.com>,
        Mingwei Zhang <mizhang@google.com>
Content-Type: text/plain; charset="UTF-8"
Precedence: bulk

Explicitly check for a REMOVED leaf SPTE prior to attempting to map
the final SPTE when handling a TDP MMU fault.  Functionally, this is a
nop as tdp_mmu_set_spte_atomic() will eventually detect the frozen SPTE.
Pre-checking for a REMOVED SPTE is a minor optmization, but the real goal
is to allow tdp_mmu_set_spte_atomic() to have an invariant that the "old"
SPTE is never a REMOVED SPTE.

Signed-off-by: Sean Christopherson <seanjc@google.com>
---
 arch/x86/kvm/mmu/tdp_mmu.c | 6 +++++-
 1 file changed, 5 insertions(+), 1 deletion(-)

diff --git a/arch/x86/kvm/mmu/tdp_mmu.c b/arch/x86/kvm/mmu/tdp_mmu.c
index 4151e61245a7..1acd12bf309f 100644
--- a/arch/x86/kvm/mmu/tdp_mmu.c
+++ b/arch/x86/kvm/mmu/tdp_mmu.c
@@ -1250,7 +1250,11 @@ int kvm_tdp_mmu_map(struct kvm_vcpu *vcpu, struct kvm_page_fault *fault)
 		}
 	}
 
-	if (iter.level != fault->goal_level) {
+	/*
+	 * Force the guest to retry the access if the upper level SPTEs aren't
+	 * in place, or if the target leaf SPTE is frozen by another CPU.
+	 */
+	if (iter.level != fault->goal_level || is_removed_spte(iter.old_spte)) {
 		rcu_read_unlock();
 		return RET_PF_RETRY;
 	}
-- 
2.35.1.574.g5d30c73bfb-goog