Re: Question about supporting AMD eGPU hot plug case

[Andrey Grodzovsky <andrey.grodzovsky@amd.com>]

On 2021-03-12 4:03 a.m., Christian König wrote:
> Am 11.03.21 um 23:40 schrieb Andrey Grodzovsky:
>> [SNIP]
>>>> The expected result is they all move closer to the start of PCI address
>>>> space.
>>>>
>>>
>>> Ok, I updated as you described. Also I removed PCI conf command to stop
>>> address decoding and restart later as I noticed PCI core does it itself
>>> when needed.
>>> I tested now also with graphic desktop enabled while submitting
>>> 3d draw commands and seems like under this scenario everything still
>>> works. Again, this all needs to be tested with VRAM BAR move as then
>>> I believe I will see more issues like handling of MMIO mapped VRAM 
>>> objects (like GART table). In case you do have an AMD card you could 
>>> also maybe give it a try. In the meanwhile I will add support to 
>>> ioremapping of those VRAM objects.
>>>
>>> Andrey
>>
>> Just an update, added support for unmaping/remapping of all VRAM
>> objects, both user space mmaped and kernel ioremaped. Seems to work
>> ok but again, without forcing VRAM BAR to move I can't be sure.
>> Alex, Chsristian - take a look when you have some time to give me some
>> initial feedback on the amdgpu side.
>>
>> The code is at 
>> https://cgit.freedesktop.org/~agrodzov/linux/log/?h=yadro%2Fpcie_hotplug%2Fmovable_bars_v9.1 
>>
> 
> Mhm, that let's userspace busy retry until the BAR movement is done.
> 
> Not sure if that can't live lock somehow.
> 
> Christian.

In my testing it didn't but, I can instead route them to some
global static dummy page while BARs are moving and then when everything
done just invalidate the device address space again and let the
pagefaults fill in valid PFNs again.

Andrey

> 
>>
>> Andrey
>