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

Christoffer Dall
2017-10-18T16:47:50Z

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 <cdall@linaro.org>
> > ---
> > 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