[PATCH 1/3] KVM: arm64: nv: only emulate timers that have not yet fired

[Ganapatrao Kulkarni]

From: D Scott Phillips <scott at os.amperecomputing.com>

The timer emulation logic goes into an infinite loop when the NestedVM(L2)
timer is being emulated.

While the CPU is executing in L1 context, the L2 timers are emulated using
host hrtimer. When the delta of cval and current time reaches zero, the
vtimer interrupt is fired/forwarded to L2, however the emulation function
in Host-Hypervisor(L0) is still restarting the hrtimer with an expiry time
set to now, triggering hrtimer to fire immediately and resulting in a
continuous trigger of hrtimer and endless looping in the timer emulation.

Adding a fix to avoid restarting of the hrtimer if the interrupt is
already fired.

Signed-off-by: D Scott Phillips <scott at os.amperecomputing.com>
Signed-off-by: Ganapatrao Kulkarni <gankulkarni at os.amperecomputing.com>
---
 arch/arm64/kvm/arch_timer.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/arch/arm64/kvm/arch_timer.c b/arch/arm64/kvm/arch_timer.c
index 2371796b1ab5..27a6ec46803a 100644
--- a/arch/arm64/kvm/arch_timer.c
+++ b/arch/arm64/kvm/arch_timer.c
@@ -472,7 +472,8 @@ static void timer_emulate(struct arch_timer_context *ctx)
 		return;
 	}
 
-	soft_timer_start(&ctx->hrtimer, kvm_timer_compute_delta(ctx));
+	if (!ctx->irq.level)
+		soft_timer_start(&ctx->hrtimer, kvm_timer_compute_delta(ctx));
 }
 
 static void timer_save_state(struct arch_timer_context *ctx)
-- 
2.33.1