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

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Date:	Mon, 12 Nov 2012 19:27:27 +0000
From:	Russell King - ARM Linux <linux@....linux.org.uk>
To:	Rob Clark <rob.clark@...aro.org>
Cc:	linux-arm-kernel@...ts.infradead.org, patches@...aro.org,
	linux-kernel@...r.kernel.org, linux-omap@...r.kernel.org,
	dri-devel@...ts.freedesktop.org, Arnd Bergmann <arnd@...db.de>,
	Rob Clark <rob@...com>
Subject: Re: [PATCH] ARM: add get_user() support for 8 byte types

On Fri, Nov 09, 2012 at 03:17:33PM -0600, Rob Clark wrote:
> From: Rob Clark <rob@...com>
> 
> A new atomic modeset/pageflip ioctl being developed in DRM requires
> get_user() to work for 64bit types (in addition to just put_user()).

NAK.

(I did write a better email explaining all the ins and outs of why this
won't work and why 64-bit get_user isn't possible, but my editor crapped
out and lost all that well written message; I don't fancy typing it all
out again.)

Nevertheless,
int test_ptr(unsigned int **v, unsigned int **p)
{
        return get_user(*v, p);
}

produces a warning, and you can't get away from that if you stick 64-bit
support into get_user().

Sorry, 64-bit get_user() is a no-no.
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