Re: [RFC PATCH v2 06/19] KVM: arm/arm64: Make timer_arm and timer_disarm helpers more generic

Christoffer Dall
2017-08-01T14:56:36Z

On Tue, Aug 01, 2017 at 03:10:59PM +0100, Marc Zyngier wrote:
> On 17/07/17 15:27, 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)
>
> I find it a bit confusing that the soft_timer_* functions operate on
> different object types: arch_timer_cpu for soft_timer_is_armed(), and
> hrtimer for soft_timer_start. Is there anything that prevents us from
> keeping arch_timer_cpu for all of them?
>

The problem is now we have two timers for a VCPU, one which is shared
between the two timer contexts (physical and virtual) used when the
process goes to sleep with a programmed timer, and one used to exit the
guest for the physical timer emulation. So I either need to provide
some sideband information or use the hrtimer pointer.

I tried to address this in later patches by renaming timer_is_armed() to
bg_timer_is_armed(), but I'm open to better suggestions.

> > {
> > - 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)
> > + 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);
> >
> > /*
> > * The guest could have modified the timer registers or the timer
> > @@ -615,7 +614,7 @@ void kvm_timer_vcpu_terminate(struct kvm_vcpu *vcpu)
> > struct arch_timer_cpu *timer = &vcpu->arch.timer_cpu;
> > struct arch_timer_context *vtimer = vcpu_vtimer(vcpu);
> >
> > - timer_disarm(timer);
> > + soft_timer_cancel(&timer->timer, &timer->expired);
> > kvm_vgic_unmap_phys_irq(vcpu, vtimer->irq.irq);
> > }
> >
> >
>
> Otherwise looks good to me.
>
Thanks!
-Christoffer