path: root/include/kvm/arm_arch_timer.h
diff options
authorChristoffer Dall <christoffer.dall@linaro.org>2015-03-13 17:02:55 +0000
committerChristoffer Dall <christoffer.dall@linaro.org>2015-03-14 13:48:00 +0100
commit1a74847885cc87857d631f91cca4d83924f75674 (patch)
tree3b0e150dea2b18e21d0b7538237050160ea718e1 /include/kvm/arm_arch_timer.h
parent47a98b15ba7cf6a13bd94ab8455d3f586b16420b (diff)
arm/arm64: KVM: Fix migration race in the arch timer
When a VCPU is no longer running, we currently check to see if it has a timer scheduled in the future, and if it does, we schedule a host hrtimer to notify is in case the timer expires while the VCPU is still not running. When the hrtimer fires, we mask the guest's timer and inject the timer IRQ (still relying on the guest unmasking the time when it receives the IRQ). This is all good and fine, but when migration a VM (checkpoint/restore) this introduces a race. It is unlikely, but possible, for the following sequence of events to happen: 1. Userspace stops the VM 2. Hrtimer for VCPU is scheduled 3. Userspace checkpoints the VGIC state (no pending timer interrupts) 4. The hrtimer fires, schedules work in a workqueue 5. Workqueue function runs, masks the timer and injects timer interrupt 6. Userspace checkpoints the timer state (timer masked) At restore time, you end up with a masked timer without any timer interrupts and your guest halts never receiving timer interrupts. Fix this by only kicking the VCPU in the workqueue function, and sample the expired state of the timer when entering the guest again and inject the interrupt and mask the timer only then. Signed-off-by: Christoffer Dall <christoffer.dall@linaro.org> Signed-off-by: Alex Bennée <alex.bennee@linaro.org> Signed-off-by: Christoffer Dall <christoffer.dall@linaro.org>
Diffstat (limited to 'include/kvm/arm_arch_timer.h')
1 files changed, 2 insertions, 0 deletions
diff --git a/include/kvm/arm_arch_timer.h b/include/kvm/arm_arch_timer.h
index a74e4c2bf188..e5966758c093 100644
--- a/include/kvm/arm_arch_timer.h
+++ b/include/kvm/arm_arch_timer.h
@@ -67,4 +67,6 @@ void kvm_timer_vcpu_terminate(struct kvm_vcpu *vcpu);
u64 kvm_arm_timer_get_reg(struct kvm_vcpu *, u64 regid);
int kvm_arm_timer_set_reg(struct kvm_vcpu *, u64 regid, u64 value);
+bool kvm_timer_should_fire(struct kvm_vcpu *vcpu);