KVM: fix avic_set_running for preemptable kernels

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>

diff --git a/arch/x86/kvm/svm/avic.c b/arch/x86/kvm/svm/avic.c
index affc0ea..9d6066e 100644 (file)
--- a/arch/x86/kvm/svm/avic.c
+++ b/arch/x86/kvm/svm/avic.c
@@ -989,16 +989,18 @@ 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)