On Tue, 13 Aug 2019 16:44:21 +0100,
Julien Grall <julien.grall@xxxxxxx> wrote:
>
> Hi Sebastian,
>
> On 8/13/19 1:58 PM, bigeasy@xxxxxxxxxxxxx wrote:
> > On 2019-07-27 14:37:11 [+0100], Julien Grall wrote:
> >>>> 8<------------
> >>>> --- a/virt/kvm/arm/arch_timer.c
> >>>> +++ b/virt/kvm/arm/arch_timer.c
> >>>> @@ -80,7 +80,7 @@ static inline bool userspace_irqchip(str
> >>>> static void soft_timer_start(struct hrtimer *hrt, u64 ns)
> >>>> {
> >>>> hrtimer_start(hrt, ktime_add_ns(ktime_get(), ns),
> >>>> - HRTIMER_MODE_ABS);
> >>>> + HRTIMER_MODE_ABS_HARD);
> >>>> }
> >>>
> >>> That's pretty neat, and matches the patch you already have for
> >>> x86. Feel free to add my
> >>>
> >>> Acked-by: Marc Zyngier <maz@xxxxxxxxxx>
> >>
> >> I can confirm the warning now disappeared. Feel free to added my tested-by:
> >>
> >> Tested-by: Julien Grall <julien.grall@xxxxxxx>
> >>
> >
> > |kvm_hrtimer_expire()
> > | kvm_timer_update_irq()
> > | kvm_vgic_inject_irq()
> > | vgic_lazy_init()
> > | if (unlikely(!vgic_initialized(kvm))) {
> > | if (kvm->arch.vgic.vgic_model != KVM_DEV_TYPE_ARM_VGIC_V2)
> > | return -EBUSY;
> > |
> > | mutex_lock(&kvm->lock);
> >
> > Is this possible path of any concern? This should throw a warning also
> > for !RT so probably not…
>
> Hmmm, theoretically yes. In practice, it looks like the hrtimer will
> not be started before kvm_vcpu_first_run_init() is called on the first
> run.
Exactly. Even if you restore the timer in a "firing" configuration,
you'll have to execute the vgic init before any background timer gets
programmed, let alone expired.
Yes, the interface is terrible.
> The function will call kvm_vgic_map_resources() which will initialize
> the vgic if not already done.
>
> Looking around, I think this is here to cater the case where
> KVM_IRQ_LINE is called before running.
>
> I am not yet familiar with the vgic, so I may have missed something.
>
> >
> > I prepared the patch below. This one could go straight to tglx's timer tree
> > since he has the _HARD bits there. I *think* it requires to set the bits
> > _HARD during _init() and _start() otherwise there is (or was) a warning…
> >
> > Sebastian
> > 8<------------
> >
> > From: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
> > Date: Tue, 13 Aug 2019 14:29:41 +0200
> > Subject: [PATCH] KVM: arm/arm64: Let the timer expire in hardirq context on RT
> >
> > The timers are canceled from an preempt-notifier which is invoked with
> > disabled preemption which is not allowed on PREEMPT_RT.
> > The timer callback is short so in could be invoked in hard-IRQ context
> > on -RT.
> >
> > Let the timer expire on hard-IRQ context even on -RT.
> >
> > Signed-off-by: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
> > Acked-by: Marc Zyngier <maz@xxxxxxxxxx>
> > Tested-by: Julien Grall <julien.grall@xxxxxxx>
> > Signed-off-by: Sebastian Andrzej Siewior <bigeasy@xxxxxxxxxxxxx>
> > ---
> > virt/kvm/arm/arch_timer.c | 8 ++++----
> > 1 file changed, 4 insertions(+), 4 deletions(-)
> >
> > diff --git a/virt/kvm/arm/arch_timer.c b/virt/kvm/arm/arch_timer.c
> > index 1be486d5d7cb4..0bfa7c5b5c890 100644
> > --- a/virt/kvm/arm/arch_timer.c
> > +++ b/virt/kvm/arm/arch_timer.c
> > @@ -80,7 +80,7 @@ static inline bool userspace_irqchip(struct kvm *kvm)
> > static void soft_timer_start(struct hrtimer *hrt, u64 ns)
> > {
> > hrtimer_start(hrt, ktime_add_ns(ktime_get(), ns),
> > - HRTIMER_MODE_ABS);
> > + HRTIMER_MODE_ABS_HARD);
> > }
> > static void soft_timer_cancel(struct hrtimer *hrt)
> > @@ -697,11 +697,11 @@ void kvm_timer_vcpu_init(struct kvm_vcpu *vcpu)
> > update_vtimer_cntvoff(vcpu, kvm_phys_timer_read());
> > ptimer->cntvoff = 0;
> > - hrtimer_init(&timer->bg_timer, CLOCK_MONOTONIC,
> > HRTIMER_MODE_ABS);
> > + hrtimer_init(&timer->bg_timer, CLOCK_MONOTONIC, HRTIMER_MODE_ABS_HARD);
> > timer->bg_timer.function = kvm_bg_timer_expire;
> > - hrtimer_init(&vtimer->hrtimer, CLOCK_MONOTONIC,
> > HRTIMER_MODE_ABS);
> > - hrtimer_init(&ptimer->hrtimer, CLOCK_MONOTONIC, HRTIMER_MODE_ABS);
> > + hrtimer_init(&vtimer->hrtimer, CLOCK_MONOTONIC, HRTIMER_MODE_ABS_HARD);
> > + hrtimer_init(&ptimer->hrtimer, CLOCK_MONOTONIC, HRTIMER_MODE_ABS_HARD);
> > vtimer->hrtimer.function = kvm_hrtimer_expire;
> > ptimer->hrtimer.function = kvm_hrtimer_expire;
> >
Patch looks fine, please add it to the pile of RT stuff! ;-)
Thanks,
M.
--
Jazz is not dead, it just smells funny.
