Re: [PATCH v5 4/6] io_uring: rsrc: delegate VMA file-backed check to GUP

[Jens Axboe]

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@xxxxxxxxx>
>>
> 
> Jens, please see my note regarding iouring:
> 
> https://lore.kernel.org/bpf/6e96358e-bcb5-cc36-18c3-ec5153867b9a@xxxxxxxxxx/
> 
> 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