When fully emulating a timer, we back it with a hrtimer that is
armver on vcpu_load(). However, we do this even if the timer is
already pending.
This causes spurious interrupts to be taken, though the guest
doesn't observe them (the interrupt is already pending).
Although this is a waste of precious cycles, this isn't the
end of the world with the current state of KVM. However, this
can lead to a situation where a guest doesn't make forward
progress anymore with NV.
Fix it by checking that if the timer is already pending
before arming a new hrtimer. Also drop the hrtimer cancelling,
which is useless, by construction.
Reported-by: D Scott Phillips <scott@xxxxxxxxxxxxxxxxxxxxxx>
Fixes: bee038a67487 ("KVM: arm/arm64: Rework the timer code to use a timer_map")
Signed-off-by: Marc Zyngier <maz@xxxxxxxxxx>
---
arch/arm64/kvm/arch_timer.c | 4 +---
1 file changed, 1 insertion(+), 3 deletions(-)
diff --git a/arch/arm64/kvm/arch_timer.c b/arch/arm64/kvm/arch_timer.c
index bb24a76b4224..587d87aec33f 100644
--- a/arch/arm64/kvm/arch_timer.c
+++ b/arch/arm64/kvm/arch_timer.c
@@ -428,10 +428,8 @@ static void timer_emulate(struct arch_timer_context *ctx)
* scheduled for the future. If the timer cannot fire at all,
* then we also don't need a soft timer.
*/
- if (!kvm_timer_irq_can_fire(ctx)) {
- soft_timer_cancel(&ctx->hrtimer);
+ if (should_fire || !kvm_timer_irq_can_fire(ctx))
return;
- }
soft_timer_start(&ctx->hrtimer, kvm_timer_compute_delta(ctx));
}
--
2.34.1
