Re: [RFC][CFT][PATCHSET v1] uaccess unification

From	Linus Torvalds <torvalds@linux-foundation.org>
Newsgroups	linux.kernel
Subject	Re: [RFC][CFT][PATCHSET v1] uaccess unification
Date	2017-03-30 02:40 +0200
Message-ID	<tqwi5-6vs-9@gated-at.bofh.it> (permalink)
References	(1 earlier) <tqseu-3C5-27@gated-at.bofh.it> <tqsxQ-3KK-13@gated-at.bofh.it> <tqtay-4hp-21@gated-at.bofh.it> <tqvvH-5PF-9@gated-at.bofh.it> <tqvP3-6cP-9@gated-at.bofh.it>
Organization	linux.* mail to news gateway

Show all headers | View raw

On Wed, Mar 29, 2017 at 5:02 PM, Vineet Gupta
<Vineet.Gupta1@synopsys.com> wrote:
>
> I guess I can in next day or two - but mind you the inline version for ARC is kind
> of special vs. other arches. We have this "manual" constant propagation to elide
> the unrolled LD/ST for 1-15 byte stragglers, when @sz is constant.

I don't think that's special. We do that on x86 too, and I suspect ARC
copied it from there (or from somebody else who did it).

But at least on x86 is is limited entirely to the "__" versions, and
it's almost entirely pointless. We actually removed some of that kind
of code because it was *do* pointless, and it had just been copied
around into the "atomic" versions too.

See for example commit bd28b14591b9 ("x86: remove more uaccess_32.h
complexity"), which did that.

The basic "__" versions still do that constant-size thing, but they
really are questionable. Exactly because it's just the "__" versions -
the *regular* "copy_to/from_user()" is an unconditional function call,
because inlining it isn't just the access operations, it's the size
check, and on modern x86 it's also the "set AC to mark the user access
as safe".

.. and many distros enable some of the might_sleep() debugging code
etc. With any of that, inlining is simply a *bad* choice.

                  Linus

Thread

[RFC][CFT][PATCHSET v1] uaccess unification Al Viro <viro@ZenIV.linux.org.uk> - 2017-03-29 08:00 +0200
  Re: [RFC][CFT][PATCHSET v1] uaccess unification Vineet Gupta <Vineet.Gupta1@synopsys.com> - 2017-03-29 22:20 +0200
    Re: [RFC][CFT][PATCHSET v1] uaccess unification Linus Torvalds <torvalds@linux-foundation.org> - 2017-03-29 22:40 +0200
      Re: [RFC][CFT][PATCHSET v1] uaccess unification Al Viro <viro@ZenIV.linux.org.uk> - 2017-03-29 23:10 +0200
        Re: [RFC][CFT][PATCHSET v1] uaccess unification Linus Torvalds <torvalds@linux-foundation.org> - 2017-03-29 23:30 +0200
          Re: [RFC][CFT][PATCHSET v1] uaccess unification Al Viro <viro@ZenIV.linux.org.uk> - 2017-03-30 01:20 +0200
            Re: [RFC][CFT][PATCHSET v1] uaccess unification Linus Torvalds <torvalds@linux-foundation.org> - 2017-03-30 01:50 +0200
              Re: [RFC][CFT][PATCHSET v1] uaccess unification Al Viro <viro@ZenIV.linux.org.uk> - 2017-03-30 17:40 +0200
    Re: [RFC][CFT][PATCHSET v1] uaccess unification Al Viro <viro@ZenIV.linux.org.uk> - 2017-03-29 22:40 +0200
      Re: [RFC][CFT][PATCHSET v1] uaccess unification Vineet Gupta <Vineet.Gupta1@synopsys.com> - 2017-03-29 23:20 +0200
        Re: [RFC][CFT][PATCHSET v1] uaccess unification Al Viro <viro@ZenIV.linux.org.uk> - 2017-03-30 01:50 +0200
          Re: [RFC][CFT][PATCHSET v1] uaccess unification Vineet Gupta <Vineet.Gupta1@synopsys.com> - 2017-03-30 02:10 +0200
            Re: [RFC][CFT][PATCHSET v1] uaccess unification Linus Torvalds <torvalds@linux-foundation.org> - 2017-03-30 02:40 +0200
              Re: [RFC][CFT][PATCHSET v1] uaccess unification Al Viro <viro@ZenIV.linux.org.uk> - 2017-03-30 03:20 +0200
              Re: [RFC][CFT][PATCHSET v1] uaccess unification Vineet Gupta <Vineet.Gupta1@synopsys.com> - 2017-03-30 22:50 +0200
                Re: [RFC][CFT][PATCHSET v1] uaccess unification Linus Torvalds <torvalds@linux-foundation.org> - 2017-03-30 23:10 +0200
                Re: [RFC][CFT][PATCHSET v1] uaccess unification Russell King - ARM Linux <linux@armlinux.org.uk> - 2017-03-31 01:30 +0200
  Re: [RFC][CFT][PATCHSET v1] uaccess unification Martin Schwidefsky <schwidefsky@de.ibm.com> - 2017-03-30 14:40 +0200
    Re: [RFC][CFT][PATCHSET v1] uaccess unification Al Viro <viro@ZenIV.linux.org.uk> - 2017-03-30 16:50 +0200
  Re: [RFC][CFT][PATCHSET v1] uaccess unification Russell King - ARM Linux <linux@armlinux.org.uk> - 2017-03-30 18:30 +0200
    Re: [RFC][CFT][PATCHSET v1] uaccess unification Al Viro <viro@ZenIV.linux.org.uk> - 2017-03-30 18:50 +0200
      Re: [RFC][CFT][PATCHSET v1] uaccess unification Linus Torvalds <torvalds@linux-foundation.org> - 2017-03-30 19:20 +0200
        Re: [RFC][CFT][PATCHSET v1] uaccess unification Al Viro <viro@ZenIV.linux.org.uk> - 2017-03-30 20:50 +0200
          Re: [RFC][CFT][PATCHSET v1] uaccess unification Linus Torvalds <torvalds@linux-foundation.org> - 2017-03-30 21:00 +0200
          Re: [RFC][CFT][PATCHSET v1] uaccess unification Al Viro <viro@ZenIV.linux.org.uk> - 2017-03-30 21:00 +0200
            Re: [RFC][CFT][PATCHSET v1] uaccess unification Linus Torvalds <torvalds@linux-foundation.org> - 2017-03-30 21:00 +0200
              Re: [RFC][CFT][PATCHSET v1] uaccess unification Al Viro <viro@ZenIV.linux.org.uk> - 2017-03-30 21:20 +0200
                Re: [RFC][CFT][PATCHSET v1] uaccess unification Linus Torvalds <torvalds@linux-foundation.org> - 2017-03-30 21:30 +0200
                Re: [RFC][CFT][PATCHSET v1] uaccess unification Al Viro <viro@ZenIV.linux.org.uk> - 2017-03-30 23:20 +0200
  Re: [RFC][CFT][PATCHSET v1] uaccess unification Kees Cook <keescook@chromium.org> - 2017-03-31 02:30 +0200
    Re: [RFC][CFT][PATCHSET v1] uaccess unification James Hogan <james.hogan@imgtec.com> - 2017-03-31 15:40 +0200
  Re: [RFC][CFT][PATCHSET v1] uaccess unification James Morse <james.morse@arm.com> - 2017-04-03 18:30 +0200
  Re: [RFC][CFT][PATCHSET v1] uaccess unification Max Filippov <jcmvbkbc@gmail.com> - 2017-04-04 22:30 +0200
    Re: [RFC][CFT][PATCHSET v1] uaccess unification Al Viro <viro@ZenIV.linux.org.uk> - 2017-04-04 23:00 +0200
  ia64 exceptions (Re: [RFC][CFT][PATCHSET v1] uaccess unification) Al Viro <viro@ZenIV.linux.org.uk> - 2017-04-05 07:10 +0200
    Re: ia64 exceptions (Re: [RFC][CFT][PATCHSET v1] uaccess unification) Al Viro <viro@ZenIV.linux.org.uk> - 2017-04-05 10:10 +0200
      Re: ia64 exceptions (Re: [RFC][CFT][PATCHSET v1] uaccess unification) Tony Luck <tony.luck@gmail.com> - 2017-04-05 20:50 +0200
        Re: ia64 exceptions (Re: [RFC][CFT][PATCHSET v1] uaccess unification) Al Viro <viro@ZenIV.linux.org.uk> - 2017-04-05 22:40 +0200
  [RFC][CFT][PATCHSET v2] uaccess unification Al Viro <viro@ZenIV.linux.org.uk> - 2017-04-07 02:30 +0200
    Re: [RFC][CFT][PATCHSET v2] uaccess unification Al Viro <viro@ZenIV.linux.org.uk> - 2017-04-07 02:40 +0200

csiph-web