Re: [PATCH v6 3/3] mm/gup: disallow FOLL_LONGTERM GUP-fast writing to file-backed mappings

On 02.05.23 15:36, Jason Gunthorpe wrote:

On Tue, May 02, 2023 at 03:28:40PM +0200, David Hildenbrand wrote:

quoted

On 02.05.23 15:10, Jason Gunthorpe wrote:

quoted

On Tue, May 02, 2023 at 03:04:27PM +0200, Christian Borntraeger wrote:
\> > We can reintroduce a flag to permit exceptions if this is really broken, are you

quoted

quoted

able to test? I don't have an s390 sat around :)

Matt (Rosato on cc) probably can. In the end, it would mean having
    <memoryBacking>
      <source type="file"/>
    </memoryBacking>

This s390 code is the least of the problems, after this series VFIO
won't startup at all with this configuration.

Good question if the domain would fail to start. I recall that IOMMUs for
zPCI are special on s390x. [1]

Not upstream they aren't.

quoted

Well, zPCI is special. I cannot immediately tell when we would trigger
long-term pinning.

zPCI uses the standard IOMMU stuff, so it uses a normal VFIO container
and the normal pin_user_pages() path.

@Christian, Matthew: would we pin all guest memory when starting the 
domain (IIRC, like on x86-64) and fail early, or only when the guest 
issues rpcit instructions to map individual pages?

-- 
Thanks,

David / dhildenb