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 NMI pending count == 2, NMI is not blocked and an
interrupt is pending, NMI pending count is decremented to execute
enable_irq_window().
Signed-off-by: Yuki Shibuya <shibuya.yk@xxxxxxxxxxxxxx>
---
arch/x86/kvm/x86.c | 12 +++++++-----
1 file changed, 7 insertions(+), 5 deletions(-)
diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
index 7236bd3..1373627 100644
--- a/arch/x86/kvm/x86.c
+++ b/arch/x86/kvm/x86.c
@@ -6087,12 +6087,14 @@ 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)) {
+ 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);
+
+ if (vcpu->arch.nmi_pending && kvm_cpu_has_injectable_intr(vcpu)
+ && kvm_x86_ops->interrupt_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
--
1.8.3.1
--
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