linux-kernel - Re: [PATCH] Add VDSO time function support for x86 32-bit kernel

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Message-ID: <50CA6E4C.6000305@zytor.com>
Date:	Thu, 13 Dec 2012 16:09:48 -0800
From:	"H. Peter Anvin" <hpa@...or.com>
To:	Andy Lutomirski <luto@...capital.net>
CC:	Stefani Seibold <stefani@...bold.net>,
	linux-kernel@...r.kernel.org, x86@...nel.org, tglx@...utronix.de,
	mingo@...hat.com, ak@...ux.intel.com, aarcange@...hat.com,
	john.stultz@...aro.org
Subject: Re: [PATCH] Add VDSO time function support for x86 32-bit kernel

On 12/13/2012 11:32 AM, Andy Lutomirski wrote:
>
> x32's vdso cheats -- x32 code can see high addresses just fine.  The
> toolchain just makes it difficult.
>
> Your best bet is probably to just map the vvar page twice -- once at
> the same address as native 32-bit mode (but only for compat tasks)
> would use and once in the usual fixmap location.  You can't use the
> fixmap for the compat mapping, though, since it would be a *user*
> address.
>
> For HPET support, you'd have to have special support.  I'd say to skip
> it for compat mode.
>

Whatever data you need you can just map it into the vdso range.  There 
really shouldn't be anything special about that at all.

The fixmap stuff is an x86-64 legacy that you don't have to worry about, 
obviously.

	-hpa

-- 
H. Peter Anvin, Intel Open Source Technology Center
I work for Intel.  I don't speak on their behalf.

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