From: Lorenzo Stoakes <lstoakes@gmail.com>
To: Jason Gunthorpe <jgg@nvidia.com>
Cc: linux-mm@kvack.org, linux-kernel@vger.kernel.org,
Andrew Morton <akpm@linux-foundation.org>,
Matthew Wilcox <willy@infradead.org>,
David Hildenbrand <david@redhat.com>,
Jens Axboe <axboe@kernel.dk>,
Pavel Begunkov <asml.silence@gmail.com>,
io-uring@vger.kernel.org
Subject: Re: [PATCH 5/7] io_uring: rsrc: use FOLL_SAME_FILE on pin_user_pages()
Date: Mon, 17 Apr 2023 14:19:16 +0100 [thread overview]
Message-ID: <b1f125c8-05ec-4b41-9b3d-165bf7694e5a@lucifer.local> (raw)
In-Reply-To: <ZD1CAvXee5E5456e@nvidia.com>
On Mon, Apr 17, 2023 at 09:56:34AM -0300, Jason Gunthorpe wrote:
> On Sat, Apr 15, 2023 at 12:27:45AM +0100, Lorenzo Stoakes wrote:
> > Commit edd478269640 ("io_uring/rsrc: disallow multi-source reg buffers")
> > prevents io_pin_pages() from pinning pages spanning multiple VMAs with
> > permitted characteristics (anon/huge), requiring that all VMAs share the
> > same vm_file.
>
> That commmit doesn't really explain why io_uring is doing such a weird
> thing.
>
> What exactly is the problem with mixing struct pages from different
> files and why of all the GUP users does only io_uring need to care
> about this?
>
> If there is no justification then lets revert that commit instead.
>
> > /* don't support file backed memory */
> > - for (i = 0; i < nr_pages; i++) {
> > - if (vmas[i]->vm_file != file) {
> > - ret = -EINVAL;
> > - break;
> > - }
> > - if (!file)
> > - continue;
> > - if (!vma_is_shmem(vmas[i]) && !is_file_hugepages(file)) {
> > - ret = -EOPNOTSUPP;
> > - break;
> > - }
> > - }
> > + file = vma->vm_file;
> > + if (file && !vma_is_shmem(vma) && !is_file_hugepages(file))
> > + ret = -EOPNOTSUPP;
> > +
>
> Also, why is it doing this?
>
> All GUP users don't work entirely right for any fops implementation
> that assumes write protect is unconditionally possible. eg most
> filesystems.
>
> We've been ignoring blocking it because it is an ABI break and it does
> sort of work in some cases.
>
I will leave this to Jens and Pavel to revert on!
> I'd rather see something like FOLL_ALLOW_BROKEN_FILE_MAPPINGS than
> io_uring open coding this kind of stuff.
>
How would the semantics of this work? What is broken? It is a little
frustrating that we have FOLL_ANON but hugetlb as an outlying case, adding
FOLL_ANON_OR_HUGETLB was another consideration...
> Jason
next prev parent reply other threads:[~2023-04-17 13:19 UTC|newest]
Thread overview: 36+ messages / expand[flat|nested] mbox.gz Atom feed top
2023-04-14 23:25 [PATCH 0/7] remove the vmas parameter from GUP APIs Lorenzo Stoakes
2023-04-14 23:27 ` [PATCH 1/7] mm/gup: remove unused vmas parameter from get_user_pages() Lorenzo Stoakes
2023-04-15 5:27 ` Greg Kroah-Hartman
2023-04-17 13:01 ` Jason Gunthorpe
2023-04-14 23:27 ` [PATCH 2/7] mm/gup: remove unused vmas parameter from pin_user_pages_remote() Lorenzo Stoakes
2023-04-17 13:02 ` Jason Gunthorpe
2023-04-14 23:27 ` [PATCH 3/7] mm/gup: remove vmas parameter from get_user_pages_remote() Lorenzo Stoakes
2023-04-15 0:25 ` Tetsuo Handa
2023-04-15 8:11 ` Lorenzo Stoakes
2023-04-17 13:09 ` Jason Gunthorpe
2023-04-17 13:13 ` Lorenzo Stoakes
2023-04-17 13:16 ` Jason Gunthorpe
2023-04-17 13:23 ` Lorenzo Stoakes
2023-04-17 15:07 ` Eric W. Biederman
2023-04-17 15:14 ` Lorenzo Stoakes
2023-04-14 23:27 ` [PATCH 4/7] mm/gup: introduce the FOLL_SAME_FILE GUP flag Lorenzo Stoakes
2023-04-17 13:14 ` Jason Gunthorpe
2023-04-17 13:25 ` Lorenzo Stoakes
2023-04-17 13:27 ` Jason Gunthorpe
2023-04-14 23:27 ` [PATCH 5/7] io_uring: rsrc: use FOLL_SAME_FILE on pin_user_pages() Lorenzo Stoakes
2023-04-17 12:56 ` Jason Gunthorpe
2023-04-17 13:19 ` Lorenzo Stoakes [this message]
2023-04-17 13:26 ` Jason Gunthorpe
2023-04-17 14:00 ` Lorenzo Stoakes
2023-04-17 14:15 ` Jason Gunthorpe
2023-04-17 15:20 ` Lorenzo Stoakes
2023-04-17 19:00 ` Lorenzo Stoakes
2023-04-17 19:24 ` Jason Gunthorpe
2023-04-17 19:45 ` Lorenzo Stoakes
2023-04-18 16:25 ` Pavel Begunkov
2023-04-18 16:35 ` Pavel Begunkov
2023-04-18 16:36 ` Jason Gunthorpe
2023-04-18 17:25 ` Pavel Begunkov
2023-04-18 18:19 ` Jason Gunthorpe
2023-04-14 23:27 ` [PATCH 6/7] mm/gup: remove vmas parameter from pin_user_pages() Lorenzo Stoakes
2023-04-14 23:27 ` [PATCH 7/7] mm/gup: remove vmas array from internal GUP functions Lorenzo Stoakes
Reply instructions:
You may reply publicly to this message via plain-text email
using any one of the following methods:
* Save the following mbox file, import it into your mail client,
and reply-to-all from there: mbox
Avoid top-posting and favor interleaved quoting:
https://en.wikipedia.org/wiki/Posting_style#Interleaved_style
* Reply using the --to, --cc, and --in-reply-to
switches of git-send-email(1):
git send-email \
--in-reply-to=b1f125c8-05ec-4b41-9b3d-165bf7694e5a@lucifer.local \
--to=lstoakes@gmail.com \
--cc=akpm@linux-foundation.org \
--cc=asml.silence@gmail.com \
--cc=axboe@kernel.dk \
--cc=david@redhat.com \
--cc=io-uring@vger.kernel.org \
--cc=jgg@nvidia.com \
--cc=linux-kernel@vger.kernel.org \
--cc=linux-mm@kvack.org \
--cc=willy@infradead.org \
/path/to/YOUR_REPLY
https://kernel.org/pub/software/scm/git/docs/git-send-email.html
* If your mail client supports setting the In-Reply-To header
via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line
before the message body.
This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for NNTP newsgroup(s).