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

[David Hildenbrand]

On 02.05.23 15:36, Jason Gunthorpe wrote:
> On Tue, May 02, 2023 at 03:28:40PM +0200, David Hildenbrand wrote:
> > On 02.05.23 15:10, Jason Gunthorpe wrote:
> > > 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
> > > > > 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.
>
> > 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