linux-kernel - [PATCH v4 25/30] KVM: x86/mmu: Check for a REMOVED leaf SPTE before making the SPTE

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Date:   Thu,  3 Mar 2022 14:38:37 -0500
From:   Paolo Bonzini <pbonzini@...hat.com>
To:     linux-kernel@...r.kernel.org, kvm@...r.kernel.org
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>,
        David Hildenbrand <david@...hat.com>,
        David Matlack <dmatlack@...gle.com>,
        Ben Gardon <bgardon@...gle.com>,
        Mingwei Zhang <mizhang@...gle.com>
Subject: [PATCH v4 25/30] KVM: x86/mmu: Check for a REMOVED leaf SPTE before making the SPTE

From: Sean Christopherson <seanjc@...gle.com>

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@...gle.com>
Reviewed-by: Ben Gardon <bgardon@...gle.com>
Message-Id: <20220226001546.360188-24-seanjc@...gle.com>
Signed-off-by: Paolo Bonzini <pbonzini@...hat.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 2456f880508d..89e6eb6640fe 100644
--- a/arch/x86/kvm/mmu/tdp_mmu.c
+++ b/arch/x86/kvm/mmu/tdp_mmu.c
@@ -1202,7 +1202,11 @@ 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;
 	}
-- 
2.31.1