lkml.org 
[lkml]   [2017]   [Jun]   [5]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
/
From
SubjectRe: [PATCH 2/5] powerpc/mm: split store_updates_sp() in two parts in do_page_fault()
Date
Christophe LEROY <christophe.leroy@c-s.fr> writes:

> Le 02/06/2017 à 14:11, Benjamin Herrenschmidt a écrit :
>> On Fri, 2017-06-02 at 11:39 +0200, Christophe LEROY wrote:
>>> The difference between get_user() and __get_user() is that get_user()
>>> performs an access_ok() in addition.
>>>
>>> Doesn't access_ok() only checks whether addr is below TASK_SIZE to
>>> ensure it is a valid user address ?
>>
>> Do you have a measurable improvement by skipping that check ? I agree
>> with your reasoning but I'm also paranoid and so I wouldn't change it
>> unless it's really worth it.
>>
>
> No I don't have. Taking into account the patch following this serie
> which limits even more the calls to get_user(), it is probably not worth
> it anymore (see https://patchwork.ozlabs.org/patch/757564/)
>
> I will then have to resubmit the entire serie (including that additional
> one), but there is no get_user_inatomic() so will have to either:
> - do the access_ok() verification inside the function

I think open coding the access_ok() check is probably the best option.

cheers

\
 
 \ /
  Last update: 2017-06-12 00:20    [W:0.067 / U:0.152 seconds]
©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site