From: Julien Grall <julien.grall@arm.com>
To: "bigeasy@linutronix.de" <bigeasy@linutronix.de>
Cc: Marc Zyngier <maz@kernel.org>,
Thomas Gleixner <tglx@linutronix.de>,
"linux-rt-users@vger.kernel.org" <linux-rt-users@vger.kernel.org>,
anna-maria@linutronix.de,
"kvmarm@lists.cs.columbia.edu" <kvmarm@lists.cs.columbia.edu>,
Julien Thierry <julien.thierry@arm.com>,
James Morse <james.morse@arm.com>,
Suzuki K Poulose <suzuki.poulose@arm.com>,
Andre Przywara <andre.przywara@arm.com>
Subject: Re: KVM Arm64 and Linux-RT issues
Date: Tue, 13 Aug 2019 16:44:21 +0100 [thread overview]
Message-ID: <adc0b2e2-3a2e-5685-8eb5-2ce927d2139e@arm.com> (raw)
In-Reply-To: <20190813125835.5v26s4iuv44lw2xg@linutronix.de>
Hi Sebastian,
On 8/13/19 1:58 PM, bigeasy@linutronix.de 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@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…
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.
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@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;
>
>
--
Julien Grall
next prev parent reply other threads:[~2019-08-13 15:44 UTC|newest]
Thread overview: 13+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-07-23 17:58 KVM Arm64 and Linux-RT issues 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
2019-08-13 15:44 ` Julien Grall [this message]
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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