On Wed, 24 Aug 2022 07:03:02 +0100,
Ganapatrao Kulkarni <gankulkarni@xxxxxxxxxxxxxxxxxxxxxx> wrote:
>
> From: D Scott Phillips <scott@xxxxxxxxxxxxxxxxxxxxxx>
>
> 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@xxxxxxxxxxxxxxxxxxxxxx>
> Signed-off-by: Ganapatrao Kulkarni <gankulkarni@xxxxxxxxxxxxxxxxxxxxxx>
> ---
> 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)
I think this is a regression introduced by bee038a67487 ("KVM:
arm/arm64: Rework the timer code to use a timer_map"), and you can see
it because the comment in this function doesn't make much sense
anymore.
Does the following work for you, mostly restoring the original code?
Thanks,
M.
diff --git a/arch/arm64/kvm/arch_timer.c b/arch/arm64/kvm/arch_timer.c
index ad2a5df88810..4945c5b96f05 100644
--- a/arch/arm64/kvm/arch_timer.c
+++ b/arch/arm64/kvm/arch_timer.c
@@ -480,7 +480,7 @@ 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)) {
+ if (should_fire || !kvm_timer_irq_can_fire(ctx)) {
soft_timer_cancel(&ctx->hrtimer);
return;
}
--
Without deviation from the norm, progress is not possible.
