From: Jason Gunthorpe <jgg@nvidia.com>
To: Lorenzo Stoakes <lstoakes@gmail.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 16:24:04 -0300 [thread overview]
Message-ID: <ZD2c1CB4FmUVuMln@nvidia.com> (raw)
In-Reply-To: <b661ca21-b436-44cf-b70d-0b126989ab33@lucifer.local>
On Mon, Apr 17, 2023 at 08:00:48PM +0100, Lorenzo Stoakes wrote:
> So I don't think this route is plausible unless you were thinking of
> somehow offloading to a thread?
ah, fair enough
> In any case, if we institute the FOLL_ALLOW_BROKEN_FILE_MAPPINGS flag we
> can just drop FOLL_ANON altogether right, as this will be implied and
> hugetlb should work here too?
Well.. no, as I said read-only access to the pages works fine, so GUP
should not block that. It is only write that has issues
> Separately, I find the semantics of access_remote_vm() kind of weird, and
> with a possible mmap_lock-free future it does make me wonder whether
> something better could be done there.
Yes, it is very weird, kthread_use_mm is much nicer.
> (Section where I sound like I might be going mad) Perhaps having some means
> of context switching into the kernel portion of the remote process as if
> were a system call or soft interrupt handler and having that actually do
> the uaccess operation could be useful here?
This is the kthread_use_mm() approach, that is basically what it
does. You are suggesting to extend it to kthreads that already have a
process attached...
access_remote_vm is basically copy_to/from_user built using kmap and
GUP.
even a simple step of localizing FOLL_ANON to __access_remote_vm,
since it must have the VMA nyhow, would be an improvement.
Jason
next prev parent reply other threads:[~2023-04-17 19:24 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
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 [this message]
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
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