Reply-To: Sean Christopherson <seanjc@google.com>
Date:   Wed,  8 Dec 2021 01:52:11 +0000
In-Reply-To: <20211208015236.1616697-1-seanjc@google.com>
Message-Id: <20211208015236.1616697-2-seanjc@google.com>
Mime-Version: 1.0
References: <20211208015236.1616697-1-seanjc@google.com>
Subject: [PATCH v3 01/26] KVM: fix avic_set_running for preemptable kernels
From:   Sean Christopherson <seanjc@google.com>
To:     Paolo Bonzini <pbonzini@redhat.com>, Joerg Roedel <joro@8bytes.org>
Cc:     Sean Christopherson <seanjc@google.com>,
        Vitaly Kuznetsov <vkuznets@redhat.com>,
        Wanpeng Li <wanpengli@tencent.com>,
        Jim Mattson <jmattson@google.com>,
        Suravee Suthikulpanit <suravee.suthikulpanit@amd.com>,
        kvm@vger.kernel.org, iommu@lists.linux-foundation.org,
        linux-kernel@vger.kernel.org, Maxim Levitsky <mlevitsk@redhat.com>
Content-Type: text/plain; charset="UTF-8"
Precedence: bulk

From: Paolo Bonzini <pbonzini@redhat.com>

avic_set_running() passes the current CPU to avic_vcpu_load(), albeit
via vcpu->cpu rather than smp_processor_id().  If the thread is migrated
while avic_set_running runs, the call to avic_vcpu_load() can use a stale
value for the processor id.  Avoid this by blocking preemption over the
entire execution of avic_set_running().

Reported-by: Sean Christopherson <seanjc@google.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
Reviewed-by: Maxim Levitsky <mlevitsk@redhat.com>
Not-signed-off-by: Sean Christopherson <seanjc@google.com>
---
 arch/x86/kvm/svm/avic.c | 16 +++++++++-------
 1 file changed, 9 insertions(+), 7 deletions(-)

diff --git a/arch/x86/kvm/svm/avic.c b/arch/x86/kvm/svm/avic.c
index 1d8ada5b01f8..d7132a4551a2 100644
--- a/arch/x86/kvm/svm/avic.c
+++ b/arch/x86/kvm/svm/avic.c
@@ -997,16 +997,18 @@ void avic_vcpu_put(struct kvm_vcpu *vcpu)
 static void avic_set_running(struct kvm_vcpu *vcpu, bool is_run)
 {
 	struct vcpu_svm *svm = to_svm(vcpu);
+	int cpu = get_cpu();
 
+	WARN_ON(cpu != vcpu->cpu);
 	svm->avic_is_running = is_run;
 
-	if (!kvm_vcpu_apicv_active(vcpu))
-		return;
-
-	if (is_run)
-		avic_vcpu_load(vcpu, vcpu->cpu);
-	else
-		avic_vcpu_put(vcpu);
+	if (kvm_vcpu_apicv_active(vcpu)) {
+		if (is_run)
+			avic_vcpu_load(vcpu, cpu);
+		else
+			avic_vcpu_put(vcpu);
+	}
+	put_cpu();
 }
 
 void svm_vcpu_blocking(struct kvm_vcpu *vcpu)
-- 
2.34.1.400.ga245620fadb-goog