On 24/03/2016 06:17, Yuki Shibuya wrote:
> Non maskable interrupts (NMI) are preferred to interrupts in current
> implementation. If a NMI is pending and NMI is blocked by the result
> of nmi_allowed(), pending interrupt is not injected and
> enable_irq_window() is not executed, even if interrupts injection is
> allowed.
>
> In old kernel (e.g. 2.6.32), schedule() is often called in NMI context.
> In this case, interrupts are needed to execute iret that intends end
> of NMI. The flag of blocking new NMI is not cleared until the guest
> execute the iret, and interrupts are blocked by pending NMI. Due to
> this, iret can't be invoked in the guest, and the guest is starved
> until block is cleared by some events (e.g. canceling injection).
>
> This patch injects pending interrupts, when it's allowed, even if NMI
> is blocked. And, If an interrupts is pending after executing
> inject_pending_event(), enable_irq_window() is executed regardless of
> NMI pending counter.
>
> Signed-off-by: Yuki Shibuya <shibuya.yk@xxxxxxxxxxxxxx>
> Suggested-by: Paolo Bonzini <pbonzini@xxxxxxxxxx>
> ---
> arch/x86/kvm/x86.c | 20 ++++++++++----------
> 1 file changed, 10 insertions(+), 10 deletions(-)
>
> diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
> index 7236bd3..d4fd555 100644
> --- a/arch/x86/kvm/x86.c
> +++ b/arch/x86/kvm/x86.c
> @@ -6087,12 +6087,10 @@ static int inject_pending_event(struct kvm_vcpu *vcpu, bool req_int_win)
> }
>
> /* try to inject new event if pending */
> - if (vcpu->arch.nmi_pending) {
> - if (kvm_x86_ops->nmi_allowed(vcpu)) {
> - --vcpu->arch.nmi_pending;
> - vcpu->arch.nmi_injected = true;
> - kvm_x86_ops->set_nmi(vcpu);
> - }
> + 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 (kvm_cpu_has_injectable_intr(vcpu)) {
> /*
> * Because interrupts can be injected asynchronously, we are
> @@ -6561,10 +6559,12 @@ static int vcpu_enter_guest(struct kvm_vcpu *vcpu)
> if (inject_pending_event(vcpu, req_int_win) != 0)
> req_immediate_exit = true;
> /* enable NMI/IRQ window open exits if needed */
> - else if (vcpu->arch.nmi_pending)
> - kvm_x86_ops->enable_nmi_window(vcpu);
> - else if (kvm_cpu_has_injectable_intr(vcpu) || req_int_win)
> - kvm_x86_ops->enable_irq_window(vcpu);
> + else {
> + if (vcpu->arch.nmi_pending)
> + kvm_x86_ops->enable_nmi_window(vcpu);
> + if (kvm_cpu_has_injectable_intr(vcpu) || req_int_win)
> + kvm_x86_ops->enable_irq_window(vcpu);
> + }
>
> if (kvm_lapic_enabled(vcpu)) {
> update_cr8_intercept(vcpu);
>
Thanks, queued for 4.6 and stable.
Paolo
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