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

>>> On 23.02.15 at 17:37, <julien.grall@xxxxxxxxxx> wrote:
> On 23/02/15 15:39, Ian Campbell wrote:
>> On Mon, 2015-02-23 at 10:20 +0000, Jan Beulich wrote:
>>>>>> On 23.02.15 at 11:10, <julien.grall@xxxxxxxxxx> wrote:
>>>> Right now, there is no possibility to reset a platform device in the 
>>>> kernel. There is some discussion about it but nothing more.
>> "there is no possibility to reset a platform device" isn't quite true,
>> there is certainly a theoretical possibility (i.e. it is obviously the
>> case that a dom0 could be written to do so for at least some devices).
>> So what happens if such a dom0 arises in the future? I suppose the
>> intention is that the user would having deassigned from domU and
>> determined that there kernel has the necessary feature would do some
>> sort of xl command to assign to dom0?
> The list of things to do for resetting a device would be:
>       - Deassign device from DOMU (though it's done during destruction)
>       - Assign the device to DOM0 and map MMIO
>       - Reset the device
> But that not my concern right now. As we agreed, this feature (i.e reset
> a device) is not in the scope of this series.
> So assigning the device to DOM0 is not safe at all.

Kind of confusing - above you state "assign the device to DOM0
and map MMIO" as a prereq step for resetting the device, yet
then you state assigning it back to Dom0 is not safe. Which of the
two do you mean after all?


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