From: David Laight <David.Laight@ACULAB.COM>
To: 'Linus Torvalds' <torvalds@linux-foundation.org>,
Mateusz Guzik <mjguzik@gmail.com>, Borislav Petkov <bp@suse.de>
Cc: Alexander Potapenko <glider@google.com>,
Al Viro <viro@zeniv.linux.org.uk>,
Kees Cook <keescook@chromium.org>,
Eric Biggers <ebiggers@google.com>,
Christian Brauner <brauner@kernel.org>,
"serge@hallyn.com" <serge@hallyn.com>,
"paul@paul-moore.com" <paul@paul-moore.com>,
"linux-fsdevel@vger.kernel.org" <linux-fsdevel@vger.kernel.org>,
"linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
"linux-security-module@vger.kernel.org"
<linux-security-module@vger.kernel.org>
Subject: RE: [PATCH v3 2/2] vfs: avoid duplicating creds in faccessat if possible
Date: Sun, 5 Mar 2023 17:23:29 +0000 [thread overview]
Message-ID: <f764a4ff956c4de8b059602c539e2c4a@AcuMS.aculab.com> (raw)
In-Reply-To: <CAHk-=wh17G6zo6Rfut++SHzDgXdvtrupfSX+bNL08v=LpHU0Lg@mail.gmail.com>
From: Linus Torvalds
> Sent: 04 March 2023 20:48
>
> On Sat, Mar 4, 2023 at 12:31 PM Mateusz Guzik <mjguzik@gmail.com> wrote:
> >
> > Good news: gcc provides a lot of control as to how it inlines string
> > ops, most notably:
> > -mstringop-strategy=alg
>
> Note that any static decision is always going to be crap somewhere.
> You can make it do the "optimal" thing for any particular machine, but
> I consider that to be just garbage.
>
> What I would actually like to see is the compiler always generate an
> out-of-line call for the "big enough to not just do inline trivially"
> case, but do so with the "rep stosb/movsb" calling convention.
I think you also want it to differentiate between requests that
are known to be a whole number of words and ones that might
be byte sized.
For the kmalloc+memzero case you know you can zero a whole
number of words - so all the checks memset has to do for
byte length/alignment can be removed.
The same is true for memcpy() calls used for structure copies.
The compiler knows that aligned full-word copies can be done.
So it shouldn't be calling a function that has to redo the tests.
David
-
Registered Address Lakeside, Bramley Road, Mount Farm, Milton Keynes, MK1 1PT, UK
Registration No: 1397386 (Wales)
next prev parent reply other threads:[~2023-03-05 17:23 UTC|newest]
Thread overview: 66+ messages / expand[flat|nested] mbox.gz Atom feed top
2023-01-25 15:55 [PATCH v3 1/2] capability: add cap_isidentical Mateusz Guzik
2023-01-25 15:55 ` [PATCH v3 2/2] vfs: avoid duplicating creds in faccessat if possible Mateusz Guzik
2023-02-28 0:44 ` Linus Torvalds
2023-03-02 8:30 ` Christian Brauner
2023-03-02 17:51 ` Linus Torvalds
2023-03-02 18:14 ` Mateusz Guzik
2023-03-02 18:18 ` Al Viro
2023-03-02 18:22 ` Mateusz Guzik
2023-03-02 18:43 ` Al Viro
2023-03-02 18:51 ` Mateusz Guzik
2023-03-02 19:02 ` Al Viro
2023-03-02 19:18 ` Al Viro
2023-03-02 19:03 ` Linus Torvalds
2023-03-02 19:10 ` Linus Torvalds
2023-03-02 19:19 ` Al Viro
2023-03-02 19:54 ` Kees Cook
2023-03-02 20:11 ` Al Viro
2023-03-03 15:30 ` Alexander Potapenko
2023-03-03 17:39 ` Mateusz Guzik
2023-03-03 17:54 ` Linus Torvalds
2023-03-03 19:37 ` Mateusz Guzik
2023-03-03 19:38 ` Mateusz Guzik
2023-03-03 20:08 ` Linus Torvalds
2023-03-03 20:39 ` Mateusz Guzik
2023-03-03 20:58 ` Linus Torvalds
2023-03-03 21:09 ` Mateusz Guzik
2023-03-04 19:01 ` Mateusz Guzik
2023-03-04 20:31 ` Mateusz Guzik
2023-03-04 20:48 ` Linus Torvalds
2023-03-05 17:23 ` David Laight [this message]
2023-03-04 1:29 ` Linus Torvalds
2023-03-04 3:25 ` Yury Norov
2023-03-04 3:42 ` Linus Torvalds
2023-03-04 5:51 ` Yury Norov
2023-03-04 16:41 ` David Vernet
2023-03-04 19:02 ` Linus Torvalds
2023-03-04 19:19 ` Linus Torvalds
2023-03-04 20:34 ` Linus Torvalds
2023-03-04 20:51 ` Yury Norov
2023-03-04 21:01 ` Linus Torvalds
2023-03-04 21:03 ` Linus Torvalds
2023-03-04 21:10 ` Linus Torvalds
2023-03-04 23:08 ` Linus Torvalds
2023-03-04 23:52 ` Linus Torvalds
[not found] ` <CA+icZUUH-J3eh=PSEcaHRDtcKB9svA2Qct6RiOq_MFP_+KeBLQ@mail.gmail.com>
2023-03-05 18:17 ` Linus Torvalds
2023-03-05 18:43 ` Linus Torvalds
2023-03-06 5:43 ` Yury Norov
2023-03-04 20:18 ` Al Viro
2023-03-04 20:42 ` Mateusz Guzik
2023-03-02 19:38 ` Kees Cook
2023-03-02 19:48 ` Eric Biggers
2023-03-02 18:41 ` Al Viro
2023-03-03 14:49 ` Christian Brauner
2023-03-02 18:11 ` Al Viro
2023-03-03 14:27 ` Christian Brauner
2023-02-28 1:14 ` [PATCH v3 1/2] capability: add cap_isidentical Linus Torvalds
2023-02-28 2:46 ` Casey Schaufler
2023-02-28 14:47 ` Mateusz Guzik
2023-02-28 19:39 ` Linus Torvalds
2023-02-28 19:51 ` Linus Torvalds
2023-02-28 20:48 ` Linus Torvalds
2023-02-28 21:21 ` Mateusz Guzik
2023-02-28 21:29 ` Linus Torvalds
2023-03-01 18:13 ` Linus Torvalds
2023-02-28 17:32 ` Serge E. Hallyn
2023-02-28 17:52 ` Casey Schaufler
Reply instructions:
You may reply publicly to this message via plain-text email
using any one of the following methods:
* Save the following mbox file, import it into your mail client,
and reply-to-all from there: mbox
Avoid top-posting and favor interleaved quoting:
https://en.wikipedia.org/wiki/Posting_style#Interleaved_style
* Reply using the --to, --cc, and --in-reply-to
switches of git-send-email(1):
git send-email \
--in-reply-to=f764a4ff956c4de8b059602c539e2c4a@AcuMS.aculab.com \
--to=david.laight@aculab.com \
--cc=bp@suse.de \
--cc=brauner@kernel.org \
--cc=ebiggers@google.com \
--cc=glider@google.com \
--cc=keescook@chromium.org \
--cc=linux-fsdevel@vger.kernel.org \
--cc=linux-kernel@vger.kernel.org \
--cc=linux-security-module@vger.kernel.org \
--cc=mjguzik@gmail.com \
--cc=paul@paul-moore.com \
--cc=serge@hallyn.com \
--cc=torvalds@linux-foundation.org \
--cc=viro@zeniv.linux.org.uk \
/path/to/YOUR_REPLY
https://kernel.org/pub/software/scm/git/docs/git-send-email.html
* If your mail client supports setting the In-Reply-To header
via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line
before the message body.
This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for NNTP newsgroup(s).