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

Greg Kroah-Hartman
2021-12-06T15:55:21Z

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(-)

--- 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)