On Tue, Apr 14, 2020 at 04:11:07PM -0400, Cathy Avery wrote:
> With NMI intercept moved to check_nested_events there is a race
> condition where vcpu->arch.nmi_pending is set late causing
How is nmi_pending set late? The KVM_{G,S}ET_VCPU_EVENTS paths can't set
it because the current KVM_RUN thread holds the mutex, and the only other
call to process_nmi() is in the request path of vcpu_enter_guest, which has
already executed.
> the execution of check_nested_events to not setup correctly
> for nested.exit_required. A second call to check_nested_events
> allows the injectable nmi to be detected in time in order to
> require immediate exit from L2 to L1.
>
> Signed-off-by: Cathy Avery <cavery@xxxxxxxxxx>
> ---
> arch/x86/kvm/x86.c | 15 +++++++++++----
> 1 file changed, 11 insertions(+), 4 deletions(-)
>
> diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
> index 027dfd278a97..ecfafcd93536 100644
> --- a/arch/x86/kvm/x86.c
> +++ b/arch/x86/kvm/x86.c
> @@ -7734,10 +7734,17 @@ static int inject_pending_event(struct kvm_vcpu *vcpu)
> vcpu->arch.smi_pending = false;
> ++vcpu->arch.smi_count;
> enter_smm(vcpu);
> - } else if (vcpu->arch.nmi_pending && kvm_x86_ops.nmi_allowed(vcpu)) {
> - --vcpu->arch.nmi_pending;
> - vcpu->arch.nmi_injected = true;
> - kvm_x86_ops.set_nmi(vcpu);
> + } else if (vcpu->arch.nmi_pending) {
> + if (is_guest_mode(vcpu) && kvm_x86_ops.check_nested_events) {
> + r = kvm_x86_ops.check_nested_events(vcpu);
> + if (r != 0)
> + return r;
> + }
> + if (kvm_x86_ops.nmi_allowed(vcpu)) {
> + --vcpu->arch.nmi_pending;
> + vcpu->arch.nmi_injected = true;
> + kvm_x86_ops.set_nmi(vcpu);
> + }
> } else if (kvm_cpu_has_injectable_intr(vcpu)) {
> /*
> * Because interrupts can be injected asynchronously, we are
> --
> 2.20.1
>
