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

[Matthew Rosato]

On 5/2/23 9:28 AM, 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]

Eh, well what you referenced there never merged.  We will eventually do something like this, but via iommufd.  But right now s390 is still using vfio type1 iommu

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

Enabling a zPCI device in a QEMU guest when using zPCI interpretation facilities

> 
> [1] https://www.mail-archive.com/qemu-devel@xxxxxxxxxx/msg875728.html
>