UPSTREAM: 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.
BUG=chromium:846515
TEST=build/boot on hana with USE=kvm_host
Change-Id: Ifecfecea131c45a603d73a95efb0be140e753e9c
Signed-off-by: Christoffer Dall <christoffer.dall@linaro.org>
Signed-off-by: Alex Benne <alex.bennee@linaro.org>
Signed-off-by: Christoffer Dall <christoffer.dall@linaro.org>
(cherry picked from commit 1a74847885cc87857d631f91cca4d83924f75674)
Signed-off-by: Sonny Rao <sonnyrao@chromium.org>
Reviewed-on: https://chromium-review.googlesource.com/1088072
Commit-Ready: ChromeOS CL Exonerator Bot <chromiumos-cl-exonerator@appspot.gserviceaccount.com>
3 files changed
