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From: "bigeasy@linutronix.de" <bigeasy@linutronix.de>
To: Julien Grall <julien.grall@arm.com>
Cc: "linux-rt-users@vger.kernel.org" <linux-rt-users@vger.kernel.org>,
	Marc Zyngier <maz@kernel.org>,
	Thomas Gleixner <tglx@linutronix.de>,
	anna-maria@linutronix.de,
	"kvmarm@lists.cs.columbia.edu" <kvmarm@lists.cs.columbia.edu>
Subject: Re: KVM Arm64 and Linux-RT issues
Date: Tue, 13 Aug 2019 14:58:35 +0200
Message-ID: <20190813125835.5v26s4iuv44lw2xg@linutronix.de> (raw)
In-Reply-To: <960b5ed1-6d0f-3cee-da37-6061b4946c1a@arm.com>

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@kernel.org>
> 
> I can confirm the warning now disappeared. Feel free to added my tested-by:
> 
> Tested-by: Julien Grall <julien.grall@arm.com>
> 

|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…

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@linutronix.de>
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@linutronix.de>
Acked-by: Marc Zyngier <maz@kernel.org>
Tested-by: Julien Grall <julien.grall@arm.com>
Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
---
 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;
 
-- 
2.23.0.rc1

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Thread overview: 13+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2019-07-23 17:58 Julien Grall
2019-07-24  8:53 ` Marc Zyngier
2019-07-26 22:58   ` Thomas Gleixner
2019-07-27 11:13     ` Marc Zyngier
2019-07-27 13:37       ` Julien Grall
2019-08-13 12:58         ` bigeasy [this message]
2019-08-13 15:44           ` Julien Grall
2019-08-13 16:24             ` Marc Zyngier
2019-08-16 15:18               ` Julien Grall
2019-08-16 15:23                 ` Sebastian Andrzej Siewior
2019-08-16 16:32                   ` Julien Grall
2019-08-19  7:33                     ` Sebastian Andrzej Siewior
2019-08-20 14:18                       ` Julien Grall

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