[PATCH] KVM: arm/arm64: Fix occasional warning from the timer work function

[Christoffer Dall]

When a VCPU blocks (WFI) we arm (the verb, not the architecture) any
timers scheduled to expire in the future to wake up the vcpu thread when
appropriate.  Because such as wake up involves a vcpu kick, and the
timer expire function can get called from interrupt context, and the
kick may sleep, we have to schedule the kick in the work function.

The work function currently has a warning that gets raised if it turns
out that the timer shouldn't fire when it's run, which was added because
the idea was that then the work should never have been cancelled.

However, the work function can run long after a vcpu thread gets
scheduled again and the timer conditions can have changed as a result of
running the vcpu, which would raise this warning.  This can happen on a
busy system, for example.

The solution is to simply not raise this warning, because a kick is
never harmful.  Also, cancel any scheduled work when the vcpu thread is
running anyway, since there is no need to run the work function anymore.

Reported-by: Matthias Brugger <mbrugger at suse.com>
Acked-by: Marc Zyngier <marc.zyngier at arm.com>
Signed-off-by: Christoffer Dall <christoffer.dall at linaro.org>
---
 virt/kvm/arm/arch_timer.c | 5 +++--
 1 file changed, 3 insertions(+), 2 deletions(-)

diff --git a/virt/kvm/arm/arch_timer.c b/virt/kvm/arm/arch_timer.c
index 27a1f63..e136902 100644
--- a/virt/kvm/arm/arch_timer.c
+++ b/virt/kvm/arm/arch_timer.c
@@ -91,8 +91,6 @@ static void kvm_timer_inject_irq_work(struct work_struct *work)
 	vcpu = container_of(work, struct kvm_vcpu, arch.timer_cpu.expired);
 	vcpu->arch.timer_cpu.armed = false;
 
-	WARN_ON(!kvm_timer_should_fire(vcpu));
-
 	/*
 	 * If the vcpu is blocked we want to wake it up so that it will see
 	 * the timer has expired when entering the guest.
@@ -240,6 +238,9 @@ void kvm_timer_unschedule(struct kvm_vcpu *vcpu)
 {
 	struct arch_timer_cpu *timer = &vcpu->arch.timer_cpu;
 	timer_disarm(timer);
+
+	/* No need for another thread to kick us if we're already running */
+	cancel_work_sync(&timer->expired);
 }
 
 /**
-- 
2.9.0