Re: [PATCH v4 05/11] iommu/sva: Assign a PASID to mm on PASID allocation and free it on mm exit

[Jean-Philippe Brucker]

On Tue, Apr 26, 2022 at 08:27:00AM -0700, Dave Hansen wrote:
> On 4/25/22 09:40, Jean-Philippe Brucker wrote:
> > The problem is that we'd have to request the device driver to stop DMA
> > before we can destroy the context and free the PASID. We did consider
> > doing this in the release() MMU notifier, but there were concerns about
> > blocking mmput() for too long (for example
> > https://lore.kernel.org/linux-iommu/4d68da96-0ad5-b412-5987-2f7a6aa796c3@xxxxxxx/
> > though I think there was a more recent discussion). We also need to drain
> > the PRI and fault queues to get rid of all references to that PASID.
> 
> Is the concern truly about blocking mmput() itself?  Or, is it about
> releasing the resources associated with the mm?

The latter I think, this one was about releasing pages as fast as possible
if the process is picked by the OOM killer. 

Thanks,
Jean