Re: [Xen-devel] [PATCH] xen/arm: IRQ: Protect IRQ to be shared between domains and XEN

[Julien Grall <julien.grall@xxxxxxxxxx>]

On 01/15/2014 01:40 PM, Ian Campbell wrote:
> On Fri, 2014-01-10 at 20:50 +0000, Julien Grall wrote:
>> The current dt_route_irq_to_guest implementation set IRQ_GUEST no matter if 
>> the
>> IRQ is correctly setup.
>>
>> As IRQ can be shared between devices, if the devices are not assigned to the
>> same domain or Xen, this could result to IRQ route to the domain instead of
>> Xen ...
>>
>> Also avoid to rely on wrong behaviour when Xen is routing an IRQ to DOM0.
>>
>> Signed-off-by: Julien Grall <julien.grall@xxxxxxxxxx>
> 
> Does this patch relate to or rely on " setup_dt_irq: don't enable the
> IRQ if the creation has failed" at all?

There is no relation between the 2 patches. Each one fix a different bug.

>>
>> ---
>>     Hopefully, none of the supported platforms have UARTs (the only device
>>     currently used by Xen). It would be nice to have this patch for Xen 4.4 
>> to
>>     avoid waste of time for developer.
> 
> Hrm, at some point I think we have to say no and I think post-rc "nice
> to avoid waste of time for developer" might be it. After all in a little
> over a month developers will be using 4.5-pre with this patch applied.

I'm fine to wait after Xen 4.4 release.

> What actually happens without this patch? The Xen console UART stops
> working because the IRQ is delivered to the guest and not to Xen?

Right.

> How did you discover this? Does this happen in practice on any of the
> platforms which Xen supports? I think in general shared interrupts are
> reasonably rare on ARM, especially for on-SoC peripherals which the UART
> very often will be.

By reading the code, IRQ_GUEST is set unconditionally in
dt_route_irq_to_guest.

All the current supported platform are safe.

---
Julien Grall

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