KVM: arm64: timer: Always evaluate the need for a soft timer

When updating the interrupt state for an emulated timer, we return
early and skip the setup of a soft timer that runs in parallel
with the guest.

While this is OK if we have set the interrupt pending, it is pretty
wrong if the guest moved CVAL into the future.  In that case,
no timer is armed and the guest can wait for a very long time
(it will take a full put/load cycle for the situation to resolve).

This is specially visible with EDK2 running at EL2, but still
using the EL1 virtual timer, which in that case is fully emulated.
Any key-press takes ages to be captured, as there is no UART
interrupt and EDK2 relies on polling from a timer...

The fix is simply to drop the early return. If the timer interrupt
is pending, we will still return early, and otherwise arm the soft
timer.

Fixes: 4d74ecf ("KVM: arm64: Don't arm a hrtimer for an already pending timer")
Cc: stable@vger.kernel.org
Tested-by: Dmytro Terletskyi <dmytro_terletskyi@epam.com>
Reviewed-by: Oliver Upton <oliver.upton@linux.dev>
Link: https://lore.kernel.org/r/20250204110050.150560-2-maz@kernel.org
Signed-off-by: Marc Zyngier <maz@kernel.org>

arch/arm64/kvm/arch_timer.c

@@ -471,10 +471,8 @@ static void timer_emulate(struct arch_timer_context *ctx)
 
 	trace_kvm_timer_emulate(ctx, should_fire);
 
-	if (should_fire != ctx->irq.level) {
+	if (should_fire != ctx->irq.level)
 		kvm_timer_update_irq(ctx->vcpu, should_fire, ctx);
-		return;
-	}
 
 	kvm_timer_update_status(ctx, should_fire);