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Message-ID: <a0e99a59-d304-d26e-c5f8-d8ef1bef64ff@kernel.dk>
Date:   Tue, 16 May 2023 07:19:52 -0600
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Subject: Re: [PATCH v5 4/6] io_uring: rsrc: delegate VMA file-backed check to
 GUP
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To:     David Hildenbrand <david@redhat.com>,
        Lorenzo Stoakes <lstoakes@gmail.com>, linux-mm@kvack.org,
        linux-kernel@vger.kernel.org,
        Andrew Morton <akpm@linux-foundation.org>
Cc:     Matthew Wilcox <willy@infradead.org>,
        Pavel Begunkov <asml.silence@gmail.com>,
        io-uring@vger.kernel.org, Jason Gunthorpe <jgg@ziepe.ca>,
        John Hubbard <jhubbard@nvidia.com>
References: <cover.1684097001.git.lstoakes@gmail.com>
 <642128d50f5423b3331e3108f8faf6b8ac0d957e.1684097002.git.lstoakes@gmail.com>
 <c44effe6-029e-4ccb-ce97-2ca5d5099c05@kernel.dk>
 <40ed22bb-53e3-ddc2-45ca-f0e763f26242@redhat.com>
From:   Jens Axboe <axboe@kernel.dk>
In-Reply-To: <40ed22bb-53e3-ddc2-45ca-f0e763f26242@redhat.com>
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On 5/16/23 2:25?AM, David Hildenbrand wrote:
> On 15.05.23 21:55, Jens Axboe wrote:
>> On 5/14/23 3:26?PM, Lorenzo Stoakes wrote:
>>> Now that the GUP explicitly checks FOLL_LONGTERM pin_user_pages() for
>>> broken file-backed mappings in "mm/gup: disallow FOLL_LONGTERM GUP-nonfast
>>> writing to file-backed mappings", there is no need to explicitly check VMAs
>>> for this condition, so simply remove this logic from io_uring altogether.
>>
>> Don't have the prerequisite patch handy (not in mainline yet), but if it
>> just moves the check, then:
>>
>> Reviewed-by: Jens Axboe <axboe@kernel.dk>
>>
> 
> Jens, please see my note regarding iouring:
> 
> https://lore.kernel.org/bpf/6e96358e-bcb5-cc36-18c3-ec5153867b9a@redhat.com/
> 
> With this patch, MAP_PRIVATE will work as expected (2), but there will
> be a change in return code handling (1) that we might have to document
> in the man page.

I think documenting that newer kernels will return -EFAULT rather than
-EOPNOTSUPP should be fine. It's not a new failure case, just a
different error value for an already failing case. Should be fine with
just a doc update. Will do that now.

-- 
Jens Axboe