Re: [PATCH v4 4/6] io_uring: rsrc: avoid use of vmas parameter in pin_user_pages()

[Jason Gunthorpe <jgg@nvidia.com>]

On Wed, Apr 19, 2023 at 07:45:06PM +0100, Lorenzo Stoakes wrote:

> For example, imagine if a user (yes it'd be weird) mlock'd some pages in a
> buffer and not others, then we'd break their use case. Also (perhaps?) more
> feasibly, a user might mix hugetlb and anon pages. So I think that'd be too
> restrictive here.

Yeah, I agree we should not add a broad single-vma restriction to
GUP. It turns any split of a VMA into a potentially uABI breaking
change and we just don't need that headache in the mm..

> I do like the idea of a FOLL_SINGLE_VMA for other use cases though, the
> majority of which want one and one page only. Perhaps worth taking the
> helper added in this series (get_user_page_vma_remote() from [1]) and
> replacing it with an a full GUP function which has an interface explicitly
> for this common single page/vma case.

Like I showed in another thread a function signature that can only do
one page and also returns the VMA would force it to be used properly
and we don't need a FOLL flag.

Jason