From: julien.grall@citrix•com (Julien Grall)
To: linux-arm-kernel@lists•infradead.org
Subject: [Xen-devel] xen,arm: enable cpu_hotplug
Date: Thu, 15 Oct 2015 10:58:56 +0100 [thread overview]
Message-ID: <561F78E0.2070004@citrix.com> (raw)
In-Reply-To: <561F78A4.7060507@citrix.com>
On 15/10/15 10:57, Julien Grall wrote:
> Hi Ian,
>
> On 15/10/15 09:39, Ian Campbell wrote:
>> On Thu, 2015-10-15 at 00:23 +0100, Julien Grall wrote:
>>> My second point is related to how Xen is handling interrupt with vCPU.
>>> When PSCI off is called, we will set the _VFP_down flag. This flag is
>>> used in vgic_vcpu_inject_irq and when it's set the interrupt will be
>>> ignored and stay active on the HW GIC forever. If the vCPU is coming
>>> back online, this interrupt will never be received. AFAIU the spec, the
>>> interrupt is expected to stay pending on the distributor side and will
>>> be receive when the vCPU will come back or migrate to another vCPU. A
>>> similar problem can happen when the vCPU is powered on again because we
>>> clear all the interrupt state related to vCPU (see
>>> vgic_clear_pending_irqs).
>>
>> Is there also an interaction with our implementation of ITARGETSR of
>> picking the lowest set bit? e.g. if an IRQ has target 0x6 (targeting CPU 1
>> and CPU2) we will choose CPU 1. If CPU 1 is then unplugged, will we end up
>> targeting CPU 2 or the now-offline CPU 1? In the latter case the lack of
>> interrupts might be considered surprising?
>
> I though about it when I wrote the mail yesterday night.
>
> From the spec section 1.4.3 (ARM IHI 0048B.b):
>
> "The ARM GIC architecture does not guarantee that a 1-N interrupt is
> presented to:
> ? all processors listed in the target processor list
> ? an enabled interface, where at least one interface is enabled."
>
> AFAIU this paragraph, it means that there is no guarantee to receive an
> interrupt if the target mask contain a vCPU offline.
Hmmm I may not have been clear here. I meant that the interrupt will
stay pending in the distributor but not received by the guest.
--
Julien Grall
next prev parent reply other threads:[~2015-10-15 9:58 UTC|newest]
Thread overview: 19+ messages / expand[flat|nested] mbox.gz Atom feed top
2015-10-14 17:49 xen,arm: enable cpu_hotplug Stefano Stabellini
2015-10-14 17:49 ` [PATCH 1/3] xen/arm: Enable cpu_hotplug.c Stefano Stabellini
2015-10-14 18:05 ` [Xen-devel] " Konrad Rzeszutek Wilk
2015-10-14 18:17 ` Stefano Stabellini
2015-10-16 15:21 ` Stefano Stabellini
2015-10-14 22:51 ` Julien Grall
2015-10-16 15:23 ` Stefano Stabellini
2015-10-14 17:49 ` [PATCH 2/3] xen, cpu_hotplug: call device_offline instead of cpu_down Stefano Stabellini
2015-10-14 17:49 ` [PATCH 3/3] xen/arm: don't try to re-register vcpu_info on cpu_hotplug Stefano Stabellini
2015-10-14 22:32 ` Julien Grall
2015-10-16 15:31 ` Stefano Stabellini
2015-10-14 23:23 ` xen,arm: enable cpu_hotplug Julien Grall
2015-10-15 8:39 ` [Xen-devel] " Ian Campbell
2015-10-15 9:57 ` Julien Grall
2015-10-15 9:58 ` Julien Grall [this message]
2015-10-16 15:44 ` Stefano Stabellini
2015-10-16 15:41 ` Stefano Stabellini
2015-10-16 15:45 ` Julien Grall
2015-10-16 15:45 ` Stefano Stabellini
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