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

[Julien Grall <julien.grall@xxxxxxxxxx>]

On 11/03/15 12:35, Ian Campbell wrote:
> On Tue, 2015-03-10 at 15:29 +0000, Julien Grall wrote:
>> 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?
> 
> If you didn't find it in the obvious places under xen/include/public
> then it probably doesn't exist.

Ok. I will add a comment in the patch extending XEN_DOMCTL_assign_device.

Regards,

-- 
Julien Grall

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