Fence wait in mmu_interval_notifier_ops::invalidate

[Christian König]

Am 14.12.20 um 10:52 schrieb Daniel Vetter:
> On Sun, Dec 13, 2020 at 04:09:25PM +0100, Thomas Hellström (Intel) wrote:
>> On 12/11/20 1:46 PM, Jason Gunthorpe wrote:
>>> On Fri, Dec 11, 2020 at 08:50:53AM +0100, Thomas Hellström (Intel) wrote:
>>>
>>>> My understanding of this particular case is that hardware would continue to
>>>> DMA to orphaned pages that are pinned until the driver is done with
>>>> DMA,
>>> mmu notifier replaces pinning as the locking mechanism. Drivers using
>>> mmu notifier should not be taking pins.
>>>
>>> Keep in mind this was all built for HW with real shadow page tables
>>> that can do fine grained manipulation.
>> OK yes, that makes sense and in that context the fence wait is easier to
>> understand. Looks like for example the radeon driver is using the notifier +
>> get_user_pages() but there it looks like it's used to avoid having
>> get_user_pages() clash with invalidation.
> I think the radeon userptr implementation is bad enough that Christian
> wants to outright remove it. At least he keeps talking about doing that.

Oh, yes :) Key point is having time for that.

Christian.

>
> So maybe not a good example to look at :-)
> -Daniel
>
>>> The GPU version of this to instead manipulate a command queue is a big
>>> aberration from what was intended.
>>>
>>> Jason
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