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

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

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: bee038a67487 ("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>