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[5.15,070/207] KVM: fix avic_set_running for preemptable kernels

Message ID 20211206145612.655810380@linuxfoundation.org
State New
Headers show
Series None | expand

Commit Message

Greg Kroah-Hartman Dec. 6, 2021, 2:55 p.m. UTC 
From: Paolo Bonzini <pbonzini@redhat.com>

commit 7cfc5c653b07782e7059527df8dc1e3143a7591e upstream.

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>
Fixes: 8221c1370056 ("svm: Manage vcpu load/unload when enable AVIC")
Cc: stable@vger.kernel.org
Reviewed-by: Maxim Levitsky <mlevitsk@redhat.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
---
 arch/x86/kvm/svm/avic.c |   16 +++++++++-------
 1 file changed, 9 insertions(+), 7 deletions(-)
diff mbox series

Patch

--- a/arch/x86/kvm/svm/avic.c
+++ b/arch/x86/kvm/svm/avic.c
@@ -988,16 +988,18 @@  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)