Subject: [PATCH v3 07/20] KVM: arm/arm64: Make timer_arm and timer_disarm helpers more generic

From: [email-masked] (Christoffer Dall)
Date: Wed, 18 Oct 2017 18:47:50 +0200

On Mon, Oct 09, 2017 at 06:05:04PM +0100, Marc Zyngier wrote:
> On 23/09/17 01:41, Christoffer Dall wrote:
> > We are about to add an additional soft timer to the arch timer state for
> > a VCPU and would like to be able to reuse the functions to program and
> > cancel a timer, so we make them slightly more generic and rename to make
> > it more clear that these functions work on soft timers and not the
> > hardware resource that this code is managing.
> > 
> > Signed-off-by: Christoffer Dall <[email-masked]>
> > ---
> >  virt/kvm/arm/arch_timer.c | 33 ++++++++++++++++-----------------
> >  1 file changed, 16 insertions(+), 17 deletions(-)
> > 
> > diff --git a/virt/kvm/arm/arch_timer.c b/virt/kvm/arm/arch_timer.c
> > index 8e89d63..871d8ae 100644
> > --- a/virt/kvm/arm/arch_timer.c
> > +++ b/virt/kvm/arm/arch_timer.c
> > @@ -56,26 +56,22 @@ u64 kvm_phys_timer_read(void)
> >  	return timecounter->cc->read(timecounter->cc);
> >  }
> >  
> > -static bool timer_is_armed(struct arch_timer_cpu *timer)
> > +static bool soft_timer_is_armed(struct arch_timer_cpu *timer)
> >  {
> >  	return timer->armed;
> >  }
> >  
> > -/* timer_arm: as in "arm the timer", not as in ARM the company */
> > -static void timer_arm(struct arch_timer_cpu *timer, u64 ns)
> > +static void soft_timer_start(struct hrtimer *hrt, u64 ns)
> >  {
> > -	timer->armed = true;
> > -	hrtimer_start(&timer->timer, ktime_add_ns(ktime_get(), ns),
> > +	hrtimer_start(hrt, ktime_add_ns(ktime_get(), ns),
> >  		      HRTIMER_MODE_ABS);
> >  }
> >  
> > -static void timer_disarm(struct arch_timer_cpu *timer)
> > +static void soft_timer_cancel(struct hrtimer *hrt, struct work_struct *work)
> >  {
> > -	if (timer_is_armed(timer)) {
> > -		hrtimer_cancel(&timer->timer);
> > -		cancel_work_sync(&timer->expired);
> > -		timer->armed = false;
> > -	}
> > +	hrtimer_cancel(hrt);
> > +	if (work)
> 
> When can this happen? Something in a following patch?
> 

Yeah, sorry about that.  I will point this out in the commit message.

> > +		cancel_work_sync(work);
> >  }
> >  
> >  static irqreturn_t kvm_arch_timer_handler(int irq, void *dev_id)
> > @@ -271,7 +267,7 @@ static void kvm_timer_emulate(struct kvm_vcpu *vcpu,
> >  		return;
> >  
> >  	/*  The timer has not yet expired, schedule a background timer */
> > -	timer_arm(timer, kvm_timer_compute_delta(timer_ctx));
> > +	soft_timer_start(&timer->timer, kvm_timer_compute_delta(timer_ctx));
> >  }
> >  
> >  /*
> > @@ -285,7 +281,7 @@ void kvm_timer_schedule(struct kvm_vcpu *vcpu)
> >  	struct arch_timer_context *vtimer = vcpu_vtimer(vcpu);
> >  	struct arch_timer_context *ptimer = vcpu_ptimer(vcpu);
> >  
> > -	BUG_ON(timer_is_armed(timer));
> > +	BUG_ON(soft_timer_is_armed(timer));
> >  
> >  	/*
> >  	 * No need to schedule a background timer if any guest timer has
> > @@ -306,13 +302,16 @@ void kvm_timer_schedule(struct kvm_vcpu *vcpu)
> >  	 * The guest timers have not yet expired, schedule a background timer.
> >  	 * Set the earliest expiration time among the guest timers.
> >  	 */
> > -	timer_arm(timer, kvm_timer_earliest_exp(vcpu));
> > +	timer->armed = true;
> > +	soft_timer_start(&timer->timer, kvm_timer_earliest_exp(vcpu));
> >  }
> >  
> >  void kvm_timer_unschedule(struct kvm_vcpu *vcpu)
> >  {
> >  	struct arch_timer_cpu *timer = &vcpu->arch.timer_cpu;
> > -	timer_disarm(timer);
> > +
> > +	soft_timer_cancel(&timer->timer, &timer->expired);
> > +	timer->armed = false;
> >  }
> >  
> >  static void kvm_timer_flush_hwstate_vgic(struct kvm_vcpu *vcpu)
> > @@ -448,7 +447,7 @@ 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.
> >  	 */
> > -	timer_disarm(timer);
> > +	soft_timer_cancel(&timer->timer, &timer->expired);
> 
> timer_disarm() used to set timer->armed to false, but that's not the
> case any more. Don't we risk hitting the BUG_ON() in kvm_timer_schedule
> if we hit WFI?
> 

We do, and I just didn't hit that because this goes away at the end of
the series, and I didn't vigurously test every single patch in the
series (just a compile test).

We actually only use the armed flag for the BUG_ON(), and I don't think
we need that check really.  So I suggest simply merging this logic into
this patch:

diff --git a/include/kvm/arm_arch_timer.h b/include/kvm/arm_arch_timer.h
index f0053f884b4a..d0beae98f755 100644
--- a/include/kvm/arm_arch_timer.h
+++ b/include/kvm/arm_arch_timer.h
@@ -48,9 +48,6 @@ struct arch_timer_cpu {
 	/* Work queued with the above timer expires */
 	struct work_struct		expired;
 
-	/* Background timer active */
-	bool				armed;
-
 	/* Is the timer enabled */
 	bool			enabled;
 };
diff --git a/virt/kvm/arm/arch_timer.c b/virt/kvm/arm/arch_timer.c
index 871d8ae52f9b..98643bc696a9 100644
--- a/virt/kvm/arm/arch_timer.c
+++ b/virt/kvm/arm/arch_timer.c
@@ -56,11 +56,6 @@ u64 kvm_phys_timer_read(void)
 	return timecounter->cc->read(timecounter->cc);
 }
 
-static bool soft_timer_is_armed(struct arch_timer_cpu *timer)
-{
-	return timer->armed;
-}
-
 static void soft_timer_start(struct hrtimer *hrt, u64 ns)
 {
 	hrtimer_start(hrt, ktime_add_ns(ktime_get(), ns),
@@ -281,8 +276,6 @@ void kvm_timer_schedule(struct kvm_vcpu *vcpu)
 	struct arch_timer_context *vtimer = vcpu_vtimer(vcpu);
 	struct arch_timer_context *ptimer = vcpu_ptimer(vcpu);
 
-	BUG_ON(soft_timer_is_armed(timer));
-
 	/*
 	 * No need to schedule a background timer if any guest timer has
 	 * already expired, because kvm_vcpu_block will return before putting
@@ -302,7 +295,6 @@ void kvm_timer_schedule(struct kvm_vcpu *vcpu)
 	 * The guest timers have not yet expired, schedule a background timer.
 	 * Set the earliest expiration time among the guest timers.
 	 */
-	timer->armed = true;
 	soft_timer_start(&timer->timer, kvm_timer_earliest_exp(vcpu));
 }
 
@@ -311,7 +303,6 @@ void kvm_timer_unschedule(struct kvm_vcpu *vcpu)
 	struct arch_timer_cpu *timer = &vcpu->arch.timer_cpu;
 
 	soft_timer_cancel(&timer->timer, &timer->expired);
-	timer->armed = false;
 }
 
 static void kvm_timer_flush_hwstate_vgic(struct kvm_vcpu *vcpu)

Thanks,
-Christoffer