From: Linus Torvalds <torvalds@linux-foundation.org>
To: Al Viro <viro@zeniv.linux.org.uk>
Cc: Aleksa Sarai <cyphar@cyphar.com>, Ingo Molnar <mingo@redhat.com>,
Peter Zijlstra <peterz@infradead.org>,
Alexander Shishkin <alexander.shishkin@linux.intel.com>,
Jiri Olsa <jolsa@redhat.com>, Namhyung Kim <namhyung@kernel.org>,
Christian Brauner <christian@brauner.io>,
Rasmus Villemoes <linux@rasmusvillemoes.dk>,
GNU C Library <libc-alpha@sourceware.org>,
Linux API <linux-api@vger.kernel.org>,
Linux Kernel Mailing List <linux-kernel@vger.kernel.org>
Subject: Re: [PATCH v1 1/4] lib: introduce copy_struct_from_user() helper
Date: Wed, 25 Sep 2019 13:23:27 -0700 [thread overview]
Message-ID: <CAHk-=whSHi46gH-aE8bQsv7hvKDSHpWKQyLW3qF3caAB59cH+g@mail.gmail.com> (raw)
In-Reply-To: <20190925194331.GL26530@ZenIV.linux.org.uk>
On Wed, Sep 25, 2019 at 12:43 PM Al Viro <viro@zeniv.linux.org.uk> wrote:
>
> FWIW, I would probably add a kernel-space analogue of that thing at the
> same time - check that an area is all-zeroes is not all that rare.
Hmm. Maybe.
> Another thing is that for s390 we almost certainly want something better
> than word-by-word. IIRC, word-sized userland accesses really hurt there.
> It's nowhere near as critical as with strncpy_from_user(), but with the
> same underlying issue.
Well, s390 does have those magic "area" instructions, but part of why
it's expensive on s390 is that they haven't implemented the
"user_access_begin()/end()' stuff. I think s390 could use that to at
least minimize some of the costs.
With the common case presumably being just a couple of words, it migth
not be worth it doing anything more than that even on s390.
Interestingly (or perhaps not) if I read the internal s390
implementation correctly, they kind of _have_ that concept and they
use it internally. It's just that they call it "enable_sacf_uaccess()"
and "disable_sacf_uaccess()" instead.
Linus
next prev parent reply other threads:[~2019-09-25 20:23 UTC|newest]
Thread overview: 24+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-09-25 16:59 [PATCH v1 0/4] lib: introduce copy_struct_from_user() helper Aleksa Sarai
2019-09-25 16:59 ` [PATCH v1 1/4] " Aleksa Sarai
2019-09-25 17:10 ` Linus Torvalds
2019-09-25 17:20 ` Aleksa Sarai
2019-09-25 17:48 ` Linus Torvalds
2019-09-25 18:04 ` Al Viro
2019-09-25 18:13 ` Linus Torvalds
2019-09-25 19:43 ` Al Viro
2019-09-25 20:23 ` Linus Torvalds [this message]
2019-09-25 17:18 ` Christian Brauner
2019-09-25 17:20 ` Christian Brauner
2019-09-25 19:16 ` kbuild test robot
2019-09-25 19:16 ` kbuild test robot
2019-09-25 20:47 ` kbuild test robot
2019-09-25 20:47 ` kbuild test robot
2019-09-25 16:59 ` [PATCH v1 2/4] clone3: switch to copy_struct_from_user() Aleksa Sarai
2019-09-25 17:22 ` Christian Brauner
2019-09-25 18:59 ` kbuild test robot
2019-09-25 18:59 ` kbuild test robot
2019-09-25 19:08 ` kbuild test robot
2019-09-25 19:08 ` kbuild test robot
2019-09-25 16:59 ` [PATCH v1 3/4] sched_setattr: " Aleksa Sarai
2019-09-25 16:59 ` [PATCH v1 4/4] perf_event_open: " Aleksa Sarai
2019-09-25 17:09 ` [PATCH v1 0/4] lib: introduce copy_struct_from_user() helper Christian Brauner
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