Re: [Xen-devel] [PATCH v3 18/24] xen/passthrough: iommu_deassign_device_dt: By default reassign device to nobody

[Julien Grall <julien.grall@xxxxxxxxxx>]

Hi,

On 23/02/15 15:34, Ian Campbell wrote:
> On Mon, 2015-02-23 at 10:10 +0000, Julien Grall wrote:
>>
>> On 20/02/2015 17:04, Ian Campbell wrote:
>>> On Tue, 2015-01-13 at 14:25 +0000, Julien Grall wrote:
>>>> Currently, when the device is deassigned from a domain, we directly 
>>>> reassign
>>>> to DOM0.
>>>>
>>>> As the device may not have been correctly reset, this may lead to 
>>>> corruption or
>>>> expose some part of DOM0 memory. Also, we may have no way to reset some
>>>> platform devices.
>>>>
>>>> If Xen reassigns the device to "nobody", it may receive some global/context
>>>> fault because the transaction has failed (indeed the context has been
>>>> marked invalid). Unfortunately there is no simple way to quiesce a buggy
>>>> hardware. I think we could live with that for a first version of platform
>>>> device passthrough.
>>>>
>>>> DOM0 will have to issue an hypercall to assign the device to itself if it
>>>> wants to use it.
>>>
>>> Does this behaviour differ from x86?
> 
> I realise now that x86 is a red-herring, what I really meant was differ
> from other types of device (specifically PCI ones).
> 
>>  If so then it is worth calling that
>>> out explicitly (even if not, good to know I think!)
>>
>> What do you mean by "calling that out explicitly"?
> 
> Stating in the commit log or a suitably placed comment (at least under
> xen/include/public hopefully) that deassignment of dt devices behaves
> differently to deassignment of other types of devices.

I tried to search any documentation explaining the behavior of those
DOMCTL for PCI (mostly the deassign one) but I didn't find any.

By any chance, do you know if there is one? If so where?

Regards,

-- 
Julien Grall

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