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KVM: close timer injection race window in __vcpu_run 

If a timer fires after kvm_inject_pending_timer_irqs() but before
local_irq_disable() the code will enter guest mode and only inject such
timer interrupt the next time an unrelated event causes an exit.

It would be simpler if the timer->pending irq conversion could be done
with IRQ's disabled, so that the above problem cannot happen.

For now introduce a new vcpu requests bit to cancel guest entry.

Signed-off-by: Marcelo Tosatti <mtosatti@redhat.com>
Signed-off-by: Avi Kivity <avi@qumranet.com>
This commit is contained in:
Marcelo Tosatti 2008-06-06 16:37:36 -03:00 committed by Avi Kivity
parent d4acf7e7ab
commit 06e0564566
4 changed files with 9 additions and 3 deletions
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9
arch/x86/kvm/i8254.c
View File

@ -200,9 +200,12 @@ int __pit_timer_fn(struct kvm_kpit_state *ps)
atomic_inc(&pt->pending);
smp_mb__after_atomic_inc();
if (vcpu0 && waitqueue_active(&vcpu0->wq)) {
vcpu0->arch.mp_state = KVM_MP_STATE_RUNNABLE;
wake_up_interruptible(&vcpu0->wq);
if (vcpu0) {
set_bit(KVM_REQ_PENDING_TIMER, &vcpu0->requests);
if (waitqueue_active(&vcpu0->wq)) {
vcpu0->arch.mp_state = KVM_MP_STATE_RUNNABLE;
wake_up_interruptible(&vcpu0->wq);
}
}
pt->timer.expires = ktime_add_ns(pt->timer.expires, pt->period);

1
arch/x86/kvm/lapic.c
View File

@ -940,6 +940,7 @@ static int __apic_timer_fn(struct kvm_lapic *apic)
wait_queue_head_t *q = &apic->vcpu->wq;
atomic_inc(&apic->timer.pending);
set_bit(KVM_REQ_PENDING_TIMER, &apic->vcpu->requests);
if (waitqueue_active(q)) {
apic->vcpu->arch.mp_state = KVM_MP_STATE_RUNNABLE;
wake_up_interruptible(q);

1
arch/x86/kvm/x86.c
View File

@ -2774,6 +2774,7 @@ again:
}
}
clear_bit(KVM_REQ_PENDING_TIMER, &vcpu->requests);
kvm_inject_pending_timer_irqs(vcpu);
preempt_disable();

1
include/linux/kvm_host.h
View File

@ -33,6 +33,7 @@
#define KVM_REQ_REPORT_TPR_ACCESS 2
#define KVM_REQ_MMU_RELOAD 3
#define KVM_REQ_TRIPLE_FAULT 4
#define KVM_REQ_PENDING_TIMER 5
struct kvm_vcpu;
extern struct kmem_cache *kvm_vcpu_cache;