linux-kernel - Re: [PATCH] ARM: add get_user() support for 8 byte types

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Date:	Mon, 19 Nov 2012 16:32:36 +0200
From:	Ville Syrjälä <ville.syrjala@...ux.intel.com>
To:	Arnd Bergmann <arnd@...db.de>
Cc:	Rob Clark <rob.clark@...aro.org>,
	Russell King - ARM Linux <linux@....linux.org.uk>,
	patches@...aro.org, linux-kernel@...r.kernel.org,
	dri-devel@...ts.freedesktop.org, linux-omap@...r.kernel.org,
	linux-arm-kernel@...ts.infradead.org,
	Jamie Lokier <jamie@...reable.org>
Subject: Re: [PATCH] ARM: add get_user() support for 8 byte types

On Thu, Nov 15, 2012 at 02:39:41PM +0000, Arnd Bergmann wrote:
> On Thursday 15 November 2012, Rob Clark wrote:
> > > I still haven't heard a conclusive argument why we need to use get_user()
> > > rather than copy_from_user() in the DRM code. Is this about a fast path
> > > where you want to shave off a few cycles for each call, or does this
> > > simplify the code structure, or something else?
> > 
> > well, it is mostly because it seemed like a good idea to first try to
> > solve the root issue, rather than having to fix things up in each
> > driver when someone from x86-world introduces a 64b get_user()..
> 
> As pointed out by hpa earlier, x86-32 doesn't have a 64b get_user
> either. I don't think we have a lot of drivers that are used only
> on 64-bit x86 and on 32-bit ARM but not on 32-bit x86.

Ouch. I didn't realize that x86-32 doesn't have it. All the systems
where I've run the new code are 64bit so I never noticed the problem.

I see there was a patch [1] posted a long time ago to implement 64bit
get_user() on x86-32. I wonder what happened to it?

[1] https://lkml.org/lkml/2004/4/20/96

-- 
Ville Syrjälä
Intel OTC
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