Re: [PATCH 1/2] tomoyo: Convert get_user_pages*() to pin_user_pages*()

[John Hubbard <jhubbard@nvidia.com>]

On 11/7/20 8:12 PM, Tetsuo Handa wrote:
> On 2020/11/08 11:17, John Hubbard wrote:
>>> Excuse me, but Documentation/core-api/pin_user_pages.rst says
>>> "CASE 5: Pinning in order to _write_ to the data within the page"
>>> while tomoyo_dump_page() is for "_read_ the data within the page".
>>> Do we want to convert to pin_user_pages_remote() or lock_page() ?
>>>
>>
>> Sorry, I missed the direction here, was too focused on the Case 5
>> aspect. Yes. Case 5 (which, again, I think we're about to re-document)
>> is only about *writing* to data within the page.
>>
>> So in this case, where it is just reading from the page, I think it's
>> already from a gup vs pup point of view.
>>
>> btw, it's not clear to me whether the current code is susceptible to any
>> sort of problem involving something writing to the page while it
>> is being dumped (I am curious). But changing from gup to pup wouldn't
>> fix that, if it were a problem. It a separate question from this patch.
> 
> The "struct page" tomoyo_dump_page() accesses is argv/envp arguments passed
> to execve() syscall. Therefore, these pages are not visible from threads
> except current thread, and thus there is no possibility that these pages
> are modified by other threads while current thread is reading.
> 

Perfect. So since I accidentally left out the word "correct" above (I meant
to write, "it's already correct"), let me be extra clear: Souptick, we
should just drop this patch.

thanks,
-- 
John Hubbard
NVIDIA