From: Ralf Baechle <ralf@linux-mips.org>
To: Davide Libenzi <davidel@xmailserver.org>
Cc: Linus Torvalds <torvalds@linux-foundation.org>,
Stephen Rothwell <sfr@canb.auug.org.au>,
Andrew Morton <akpm@linux-foundation.org>,
David Woodhouse <dwmw2@infradead.org>,
linux-arch@vger.kernel.org, rmk@arm.linux.org.uk,
tony.luck@intel.com
Subject: Re: [PATCH]add epoll compat code to fsl/compat.c
Date: Wed, 21 Feb 2007 22:14:49 +0000 [thread overview]
Message-ID: <20070221221449.GE8957@linux-mips.org> (raw)
In-Reply-To: <Pine.LNX.4.64.0702211259440.16904@alien.or.mcafeemobile.com>
On Wed, Feb 21, 2007 at 01:04:51PM -0800, Davide Libenzi wrote:
> > Oh, we can. "put_user()" and "get_user()" already have to work on totally
> > unaligned data. If some architecture has problems with that, they have
> > bigger issues, methinks.
> >
> > We can't trust user pointers, and that includes not trusting them being
> > aligned.
>
> Don't we get EFAULT in case of exception (access or alignment) in there?
> For "dealing with", here we'd need them to do the correct thing
> (split-load?) in case of mis-aligned access.
On an architecture which doesn't transparently handle missalignment the
best approach is to have the unalignment exception handler fix things
such that the 99.999% common case of properly aligned get_user/put_user
doesn't have to care. A few nasty architectures (Afair old ARM and the
b0rked R5900 in the Playstation 2 for 128-bit integer loads) however
don't throw exceptions so __get_user / __put_user have to handle the
problem manually which of course adds considerable overhead to the common
case.
Ralf
next prev parent reply other threads:[~2007-02-21 22:15 UTC|newest]
Thread overview: 21+ messages / expand[flat|nested] mbox.gz Atom feed top
2007-02-20 21:57 [patch 18/50] add epoll compat code to kernel/compat.c akpm
2007-02-20 23:20 ` Stephen Rothwell
2007-02-20 23:33 ` Davide Libenzi
2007-02-21 1:01 ` Stephen Rothwell
2007-02-21 1:05 ` Stephen Rothwell
2007-02-21 1:12 ` Davide Libenzi
2007-02-21 3:10 ` [PATCH]add epoll compat code to fsl/compat.c Stephen Rothwell
2007-02-21 20:24 ` Davide Libenzi
2007-02-21 20:36 ` Linus Torvalds
2007-02-21 21:04 ` Davide Libenzi
2007-02-21 21:15 ` Linus Torvalds
2007-02-22 3:07 ` David Miller
2007-02-22 4:03 ` Davide Libenzi
2007-02-22 4:39 ` Stephen Rothwell
2007-02-21 22:14 ` Ralf Baechle [this message]
2007-02-21 22:25 ` Davide Libenzi
2007-02-21 23:23 ` Ralf Baechle
2007-02-22 3:02 ` David Miller
2007-02-22 3:08 ` Davide Libenzi
2007-02-21 1:38 ` [patch 18/50] add epoll compat code to kernel/compat.c Ralf Baechle
2007-02-20 23:57 ` Andrew Morton
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