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>

1 files changed, 6 insertions, 3 deletions

diff --git a/arch/x86/kvm/i8254.c b/arch/x86/kvm/i8254.c
index f2f5d260874e..3829aa7b663f 100644
--- a/arch/x86/kvm/i8254.c
+++ b/arch/x86/kvm/i8254.c
@@ -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);