From: Linus Torvalds <torvalds@linux-foundation.org>
To: mst@redhat.com
Cc: mark.rutland@arm.com, lenaic@lhuard.fr, mhocko@suse.com,
Kees Cook <keescook@chromium.org>,
kvm@vger.kernel.org, netdev@vger.kernel.org,
liang.z.li@intel.com,
Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
virtualization@lists.linux-foundation.org, stefanha@redhat.com,
joe@perches.com, Andrew Morton <akpm@linux-foundation.org>,
mhocko@kernel.org, bijan.mottahedeh@oracle.com
Subject: Re: [PULL] vhost: cleanups and fixes
Date: Fri, 2 Nov 2018 09:14:51 -0700 [thread overview]
Message-ID: <CAHk-=wh_bQK5zs+CwQ5eyodq4sQT0eOPp60qzvVL2_EtgETP-g__18143.2555233643$1541175192$gmane$org@mail.gmail.com> (raw)
In-Reply-To: <20181102083018-mutt-send-email-mst@kernel.org>
On Fri, Nov 2, 2018 at 6:04 AM Michael S. Tsirkin <mst@redhat.com> wrote:
>
> I've tried making access_ok mask the parameter it gets.
PLEASE don't do this.
Just use "copy_to/from_user()".
We have had lots of bugs because code bitrots.
And no, the access_ok() checks aren't expensive, not even in a loop.
They *used* to be somewhat expensive compared to the access, but that
simply isn't true any more. The real expense in copy_to_user and
friends are in the user access bit setting (STAC and CLAC on x86),
which easily an order of magnitude more expensive than access_ok().
So just get rid of the double-underscore version. It's basically
always a mis-optimization due to entirely historical reasons. I can
pretty much guarantee that it's not visible in profiles.
Linus
next prev parent reply other threads:[~2018-11-02 16:14 UTC|newest]
Thread overview: 125+ messages / expand[flat|nested] mbox.gz Atom feed top
2018-11-01 21:19 [PULL] vhost: cleanups and fixes Michael S. Tsirkin
2018-11-01 21:19 ` Michael S. Tsirkin
2018-11-01 21:19 ` Michael S. Tsirkin
2018-11-01 21:44 ` Linus Torvalds
2018-11-01 21:44 ` Linus Torvalds
2018-11-01 23:00 ` Kees Cook
2018-11-01 23:00 ` Kees Cook
2018-11-01 23:00 ` Kees Cook
2018-11-01 23:06 ` Linus Torvalds
2018-11-01 23:55 ` Michael S. Tsirkin
2018-11-01 23:55 ` Michael S. Tsirkin
2018-11-02 11:46 ` Mark Rutland
2018-11-02 11:46 ` Mark Rutland
2018-11-02 13:04 ` Michael S. Tsirkin
2018-11-02 16:14 ` Linus Torvalds
2018-11-02 16:59 ` Michael S. Tsirkin
2018-11-02 16:59 ` Michael S. Tsirkin
2018-11-02 17:10 ` Linus Torvalds
2018-11-02 17:10 ` Linus Torvalds
2018-11-02 17:15 ` Linus Torvalds
2018-11-02 17:15 ` Linus Torvalds
2018-11-02 19:01 ` Al Viro
2018-11-02 19:01 ` Al Viro
2018-11-02 17:21 ` Michael S. Tsirkin
2018-11-02 17:21 ` Michael S. Tsirkin
2018-11-02 18:02 ` Linus Torvalds
2018-11-02 18:02 ` Linus Torvalds
2018-11-02 18:12 ` Michael S. Tsirkin
2018-11-02 18:12 ` Michael S. Tsirkin
2018-11-02 16:14 ` Linus Torvalds [this message]
2018-11-02 13:04 ` Michael S. Tsirkin
2018-11-30 13:44 ` Michael S. Tsirkin
2018-11-30 13:44 ` Michael S. Tsirkin
2018-11-30 19:01 ` Bijan Mottahedeh
2018-11-30 19:55 ` Michael S. Tsirkin
2018-11-30 19:55 ` Michael S. Tsirkin
2018-11-01 23:06 ` Linus Torvalds
2018-11-01 23:38 ` Michael S. Tsirkin
2018-11-01 23:38 ` Michael S. Tsirkin
-- strict thread matches above, loose matches on Subject: below --
2020-02-10 6:02 Michael S. Tsirkin
2020-02-11 2:07 ` Linus Torvalds
2020-02-11 2:07 ` Linus Torvalds
2020-02-07 7:39 Michael S. Tsirkin
2019-10-28 8:29 Michael S. Tsirkin
2019-10-15 21:19 Michael S. Tsirkin
2019-10-15 21:19 Michael S. Tsirkin
2019-10-15 22:25 ` pr-tracker-bot
2019-10-15 22:25 ` pr-tracker-bot
2019-06-03 14:30 Michael S. Tsirkin
2019-05-14 21:11 Michael S. Tsirkin
2019-05-14 21:11 Michael S. Tsirkin
2019-05-14 21:20 ` pr-tracker-bot
2019-05-14 21:20 ` pr-tracker-bot
2018-06-11 16:23 Michael S. Tsirkin
2018-06-11 16:23 ` Michael S. Tsirkin
2018-06-11 18:32 ` Linus Torvalds
2018-06-11 18:32 ` Linus Torvalds
2018-06-11 18:44 ` Linus Torvalds
2018-06-11 18:44 ` Linus Torvalds
2018-06-12 1:36 ` Michael S. Tsirkin
2018-06-12 1:36 ` Michael S. Tsirkin
2018-06-12 1:59 ` Linus Torvalds
2018-06-12 1:59 ` Linus Torvalds
2018-06-12 11:05 ` Wei Wang
2018-06-12 11:05 ` Wei Wang
2018-06-14 15:01 ` Nitesh Narayan Lal
2018-06-15 3:53 ` Wei Wang
2018-06-15 3:53 ` Wei Wang
2018-06-12 1:57 ` Michael S. Tsirkin
2018-06-12 1:57 ` Michael S. Tsirkin
2017-12-08 15:47 Michael S. Tsirkin
2017-12-08 15:47 Michael S. Tsirkin
2017-12-04 13:25 Michael S. Tsirkin
2017-08-25 18:47 Michael S. Tsirkin
2017-04-10 21:36 Michael S. Tsirkin
2017-04-10 21:36 ` Michael S. Tsirkin
2017-03-02 5:49 Michael S. Tsirkin
2017-03-02 5:49 ` Michael S. Tsirkin
2017-02-03 21:43 Michael S. Tsirkin
2017-02-03 21:43 ` Michael S. Tsirkin
2017-01-23 15:05 Michael S. Tsirkin
2017-01-23 15:05 ` Michael S. Tsirkin
2017-01-23 21:50 ` Linus Torvalds
2017-01-24 2:45 ` Michael S. Tsirkin
2017-01-24 2:45 ` Michael S. Tsirkin
2017-01-23 21:50 ` Linus Torvalds
2016-05-24 11:57 Michael S. Tsirkin
2016-05-24 11:57 ` Michael S. Tsirkin
2015-12-21 7:58 Michael S. Tsirkin
2015-12-21 7:58 ` Michael S. Tsirkin
2015-12-07 17:07 Michael S. Tsirkin
2015-09-18 10:42 Michael S. Tsirkin
2015-09-18 10:42 Michael S. Tsirkin
2015-09-09 9:15 Michael S. Tsirkin
2015-09-09 9:15 Michael S. Tsirkin
2015-07-28 10:00 Michael S. Tsirkin
2015-07-15 10:50 Michael S. Tsirkin
2015-07-15 10:50 ` Michael S. Tsirkin
2015-07-15 11:26 ` Michael S. Tsirkin
2015-07-15 11:26 ` Michael S. Tsirkin
2015-06-01 19:18 Michael S. Tsirkin
2015-06-01 19:18 Michael S. Tsirkin
2015-06-01 19:45 ` Michael S. Tsirkin
2015-06-01 19:45 ` Michael S. Tsirkin
2015-01-08 7:51 Michael S. Tsirkin
2015-01-01 12:26 Michael S. Tsirkin
2015-01-01 12:26 Michael S. Tsirkin
2014-12-18 10:46 Michael S. Tsirkin
2014-12-18 10:46 ` Michael S. Tsirkin
2014-11-13 21:22 Michael S. Tsirkin
2014-11-13 21:22 ` Michael S. Tsirkin
2014-06-25 11:05 Michael S. Tsirkin
2014-06-25 11:05 ` Michael S. Tsirkin
2013-07-15 18:31 Michael S. Tsirkin
2013-07-15 18:31 ` Michael S. Tsirkin
2013-07-22 8:07 ` Michael S. Tsirkin
2013-07-22 8:07 ` Michael S. Tsirkin
2013-07-08 11:45 Michael S. Tsirkin
2013-07-08 11:45 ` Michael S. Tsirkin
2013-05-02 10:53 Michael S. Tsirkin
2013-05-02 10:53 ` Michael S. Tsirkin
2013-05-02 18:55 ` Nicholas A. Bellinger
2013-05-02 19:33 ` Michael S. Tsirkin
2013-05-02 19:49 ` Linus Torvalds
2013-06-05 15:53 ` Michael S. Tsirkin
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