On Tue, 2021-11-30 at 03:46 -0500, Paolo Bonzini wrote:
> 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@xxxxxxxxxx>
> Signed-off-by: Paolo Bonzini <pbonzini@xxxxxxxxxx>
> ---
> 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 0a58283005f3..560807a2edd4 100644
> --- a/arch/x86/kvm/svm/avic.c
> +++ b/arch/x86/kvm/svm/avic.c
> @@ -1000,16 +1000,18 @@ 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)
To be honest, I was thinking to remove vcpu parameter from
avic_vcpu_load and let it figure it out, but this can be
always done later.
Reviewed-by: Maxim Levitsky <mlevitsk@xxxxxxxxxx>
PS: this patch as expected didn't help with the 'is_running' AVIC bug
I am stuck with.
Best regards,
Maxim Levitsky
