[Intel-gfx] [PATCH] drm/i915/gem: Allow importing of shmemfs objects into any device

[Tvrtko Ursulin]

On 20/01/2021 20:59, Chris Wilson wrote:
> Quoting Chris Wilson (2021-01-20 18:06:08)
>> Quoting Matthew Auld (2021-01-20 17:46:10)
>>> On Wed, 20 Jan 2021 at 15:40, Chris Wilson <chris at chris-wilson.co.uk> wrote:
>>>>
>>>> If we import a shmemfs object between devices, for example from
>>>> Tigerlake to DG1, we can simply reuse the native object and its backing
>>>> store.
>>>
>>> Hmmm interesting, so does that include re-using the actual sg mapping
>>> for the backing pages? Does that work out-of-the-box between different
>>> devices assuming we have iommu enabled?
>>
>> Indeed interesting; the dma_addr_t are supposed to be local to a device.
> 
> On reflection, we are expected to use cross-device dma_addr_t with
> dma-buf. It's the exporter who assigns the dma_addr_t for the importer
> to use, and they are always given from the original device.
> 
> Maybe not so bad. Definitely needs testing to see what happens in
> practice.

What about object migration? I did not spot anything preventing it once 
object was exported like this so owning device could move it to device 
memory afterwards which would probably be bad.

Regards,

Tvrtko