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Re: [Xen-devel] [PATCH for-4.12] xen/arm: irq: End cleanly spurious interrupt
- To: Stefano Stabellini <sstabellini@xxxxxxxxxx>, Julien Grall <julien.grall@xxxxxxx>
- From: Juergen Gross <jgross@xxxxxxxx>
- Date: Tue, 5 Feb 2019 06:50:33 +0100
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- Cc: xen-devel@xxxxxxxxxxxxxxxxxxxx, andre.przywara@xxxxxxx, andrii.anisov@xxxxxxxxx
- Delivery-date: Tue, 05 Feb 2019 05:50:46 +0000
- List-id: Xen developer discussion <xen-devel.lists.xenproject.org>
- Openpgp: preference=signencrypt
On 05/02/2019 01:54, Stefano Stabellini wrote:
> On Mon, 28 Jan 2019, Julien Grall wrote:
>> no_irq_type handlers are used when an IRQ does not have action attached.
>> This is useful to detect misconfiguration between the interrupt
>> controller and the software.
>>
>> Currently, all the handlers will do nothing on spurious interrupt. This
>> means if such interrupt is received, the priority of the interrupt will
>> not be dropped and the processor will lose the ability to receive any
>> interrupt lower or equal to the priority.
>>
>> Spurious interrupt can happen while releasing interrupt assigned to
>> guest (happen during domain destruction). The interaction is roughly
>>
>> CPU0 CPU1
>> release_guest_irq(A)
>> spin_lock(&desc->lock)
>> gic_remove_irq_from_guest
>> receive IRQ A
>> spin_lock(&desc->lock)
>> desc->handler->shutdown()
>> set_bit(IRQ_DISABLED)
>> desc->handler = &no_irq_type
>> spin_unlock(&desc->lock)
>> desc->handler->end();
>> spin_unlock(&desc->lock)
>>
>> Because the no_irq_type.end callback is implemented as a NOP, CPU1 will
>> not drop the priority of the interrupt. So the CPU will not be able to
>> receive any interrupt route to any guest afterwards.
>>
>> The problem can be prevented by dropping the priority and deactivating
>> the interrupt via gic_hw_ops->gic_host_irq->end().
>>
>> Note that, for now, interrupt used by Xen are safe because it is not
>> using no_irq_type on release.
>>
>> Signed-off-by: Julien Grall <julien.grall@xxxxxxx>
>
> Reviewed-by: Stefano Stabellini <sstabellini@xxxxxxxxxx>
>
> Hi Juergen,
>
> Can I have your relese ack on this fix?
Release-acked-by: Juergen Gross <jgross@xxxxxxxx>
Juergen
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