Re: [PATCH v3 08/23] vfio, mm: fix get_user_pages_remote() and FOLL_LONGTERM

John Hubbard
2019-11-13T01:08:20Z

On 11/12/19 4:58 PM, Dan Williams wrote:
...
>>> It's not redundant relative to upstream which does not do anything the
>>> FOLL_LONGTERM in the gup-slow path... but I have not looked at patches
>>> 1-7 to see if something there made it redundant.
>>
>> Oh, the hunk John had below for get_user_pages_remote() also needs to
>> call __gup_longterm_locked() when FOLL_LONGTERM is specified, then
>> that calls check_dax_vmas() which duplicates the vma_is_fsdax() check
>> above.
>
> Oh true, good eye. It is redundant if it does additionally call
> __gup_longterm_locked(), and it needs to do that otherwises it undoes
> the CMA migration magic that Aneesh added.
>

OK. So just to be clear, I'll be removing this from the patch:

/*
* The lifetime of a vaddr_get_pfn() page pin is
* userspace-controlled. In the fs-dax case this could
* lead to indefinite stalls in filesystem operations.
* Disallow attempts to pin fs-dax pages via this
* interface.
*/
if (ret > 0 && vma_is_fsdax(vmas[0])) {
ret = -EOPNOTSUPP;
put_page(page[0]);
}

(and the declaration of "vmas", as well).

thanks,
--
John Hubbard
NVIDIA