linux-kernel - Re: x86, x32: Correct invalid use of user timespec in the kernel

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Message-ID: <52EBF2BF.2090807@linux.intel.com>
Date:	Fri, 31 Jan 2014 11:00:15 -0800
From:	"H. Peter Anvin" <hpa@...ux.intel.com>
To:	Linus Torvalds <torvalds@...ux-foundation.org>
CC:	Dave Jones <davej@...hat.com>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: x86, x32: Correct invalid use of user timespec in the kernel

On 01/31/2014 10:45 AM, Linus Torvalds wrote:
> On Fri, Jan 31, 2014 at 10:06 AM, H. Peter Anvin <hpa@...ux.intel.com> wrote:
>>
>> My feeling is that {get,put}_compat_timespec() should at the very least
>> have leading underscores to flag it as a low-level function, but better
>> suggestions would be appreciated.
> 
> Why not just remove it entirely, and change all users to
> compat_[get|set]_timespec (same for timeval etc, of course).
> 
> After all, compat_*_time*() does fall back cleanly for non-x32 cases.
> And sure, maybe that particular code is never *needed* for x32
> support, but the overhead is generally zero (since in most cases X32
> isn't even configured), or very low anyway. So the upside of having
> two subtly incompatible interfaces is very dubious, no?
> 

As they both seem to be out of line, I would think so.  More than half
of the use cases are in kernel/compat.c where we could use a
double-underscore inline version if we really care -- it would probably
be a net win in terms of performance.

There are only 25 call sites in the kernel of
'(get|put)_compat_time(val|spec)' and that includes the ones inside the
larger functions.

	-hpa

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