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KVM: arm64: Don't arm a hrtimer for an already pending timer

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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@os.amperecomputing.com>
Fixes: bee038a674 ("KVM: arm/arm64: Rework the timer code to use a timer_map")
Signed-off-by: Marc Zyngier <maz@kernel.org>
Link: https://lore.kernel.org/r/20230112123829.458912-2-maz@kernel.org
Signed-off-by: Oliver Upton <oliver.upton@linux.dev>
This commit is contained in:
Marc Zyngier 2023-01-12 12:38:27 +00:00 • committed by Oliver Upton
parent b7bfaa761d
commit 4d74ecfa64
1 changed files with 1 additions and 3 deletions
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4
arch/arm64/kvm/arch_timer.c
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@ -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));
}