[PATCH v3 09/20] KVM: arm/arm64: Use separate timer for phys timer emulation

[Marc Zyngier]

On 23/09/17 01:41, Christoffer Dall wrote:
> We were using the same hrtimer for emulating the physical timer and for
> making sure a blocking VCPU thread would be eventually woken up.  That
> worked fine in the previous arch timer design, but as we are about to
> actually use the soft timer expire function for the physical timer
> emulation, change the logic to use a dedicated hrtimer.
> 
> This has the added benefit of not having to cancel any work in the sync
> path, which in turn allows us to run the flush and sync with IRQs
> disabled.
> 
> Signed-off-by: Christoffer Dall <cdall at linaro.org>
> ---
>  include/kvm/arm_arch_timer.h |  3 +++
>  virt/kvm/arm/arch_timer.c    | 18 ++++++++++++++----
>  2 files changed, 17 insertions(+), 4 deletions(-)
> 
> diff --git a/include/kvm/arm_arch_timer.h b/include/kvm/arm_arch_timer.h
> index dcbb2e1..16887c0 100644
> --- a/include/kvm/arm_arch_timer.h
> +++ b/include/kvm/arm_arch_timer.h
> @@ -47,6 +47,9 @@ struct arch_timer_cpu {
>  	/* Work queued with the above timer expires */
>  	struct work_struct		expired;
>  
> +	/* Physical timer emulation */
> +	struct hrtimer			phys_timer;
> +
>  	/* Background timer active */
>  	bool				armed;
>  
> diff --git a/virt/kvm/arm/arch_timer.c b/virt/kvm/arm/arch_timer.c
> index c2e8326..7f87099 100644
> --- a/virt/kvm/arm/arch_timer.c
> +++ b/virt/kvm/arm/arch_timer.c
> @@ -178,6 +178,12 @@ static enum hrtimer_restart kvm_bg_timer_expire(struct hrtimer *hrt)
>  	return HRTIMER_NORESTART;
>  }
>  
> +static enum hrtimer_restart kvm_phys_timer_expire(struct hrtimer *hrt)
> +{
> +	WARN(1, "Timer only used to ensure guest exit - unexpected event.");
> +	return HRTIMER_NORESTART;
> +}
> +

So what prevents this handler from actually firing? Is it that we cancel
the hrtimer while interrupts are still disabled, hence the timer never
fires? If that's the intention, then this patch is slightly out of
place, as we haven't moved the timer sync within the irq_disable() section.

Or am I missing something obvious?

>  bool kvm_timer_should_fire(struct arch_timer_context *timer_ctx)
>  {
>  	u64 cval, now;
> @@ -255,7 +261,7 @@ static void kvm_timer_update_state(struct kvm_vcpu *vcpu)
>  }
>  
>  /* Schedule the background timer for the emulated timer. */
> -static void kvm_timer_emulate(struct kvm_vcpu *vcpu,
> +static void phys_timer_emulate(struct kvm_vcpu *vcpu,
>  			      struct arch_timer_context *timer_ctx)
>  {
>  	struct arch_timer_cpu *timer = &vcpu->arch.timer_cpu;
> @@ -267,7 +273,7 @@ static void kvm_timer_emulate(struct kvm_vcpu *vcpu,
>  		return;
>  
>  	/*  The timer has not yet expired, schedule a background timer */
> -	soft_timer_start(&timer->bg_timer, kvm_timer_compute_delta(timer_ctx));
> +	soft_timer_start(&timer->phys_timer, kvm_timer_compute_delta(timer_ctx));
>  }
>  
>  /*
> @@ -424,7 +430,7 @@ void kvm_timer_flush_hwstate(struct kvm_vcpu *vcpu)
>  	kvm_timer_update_state(vcpu);
>  
>  	/* Set the background timer for the physical timer emulation. */
> -	kvm_timer_emulate(vcpu, vcpu_ptimer(vcpu));
> +	phys_timer_emulate(vcpu, vcpu_ptimer(vcpu));
>  
>  	if (unlikely(!irqchip_in_kernel(vcpu->kvm)))
>  		kvm_timer_flush_hwstate_user(vcpu);
> @@ -447,7 +453,7 @@ void kvm_timer_sync_hwstate(struct kvm_vcpu *vcpu)
>  	 * This is to cancel the background timer for the physical timer
>  	 * emulation if it is set.
>  	 */
> -	soft_timer_cancel(&timer->bg_timer, &timer->expired);
> +	soft_timer_cancel(&timer->phys_timer, NULL);

Right, that now explains the "work" test in one of the previous patches.

>  
>  	/*
>  	 * The guest could have modified the timer registers or the timer
> @@ -507,6 +513,9 @@ void kvm_timer_vcpu_init(struct kvm_vcpu *vcpu)
>  	hrtimer_init(&timer->bg_timer, CLOCK_MONOTONIC, HRTIMER_MODE_ABS);
>  	timer->bg_timer.function = kvm_bg_timer_expire;
>  
> +	hrtimer_init(&timer->phys_timer, CLOCK_MONOTONIC, HRTIMER_MODE_ABS);
> +	timer->phys_timer.function = kvm_phys_timer_expire;
> +
>  	vtimer->irq.irq = default_vtimer_irq.irq;
>  	ptimer->irq.irq = default_ptimer_irq.irq;
>  }
> @@ -615,6 +624,7 @@ void kvm_timer_vcpu_terminate(struct kvm_vcpu *vcpu)
>  	struct arch_timer_context *vtimer = vcpu_vtimer(vcpu);
>  
>  	soft_timer_cancel(&timer->bg_timer, &timer->expired);
> +	soft_timer_cancel(&timer->phys_timer, NULL);
>  	kvm_vgic_unmap_phys_irq(vcpu, vtimer->irq.irq);
>  }
>  
> 

Thanks,

	M.
-- 
Jazz is not dead. It just smells funny...