linux-kernel - Re: [PATCH 6/6] Add 32 bit VDSO support for 32 and 64 bit kernels

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Date:	Tue, 18 Dec 2012 14:24:00 -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, xemul@...allels.com, gorcunov@...nvz.org,
	andriy.shevchenko@...ux.intel.com
Subject: Re: [PATCH 6/6] Add 32 bit VDSO support for 32 and 64 bit kernels

On 12/18/2012 12:37 PM, Andy Lutomirski wrote:
>>
>> There is no introduce of new fix address. There are still there for
>> x86_64. If this will currently not a major problem on this architecture
>> than it will not for x86_32 too.
>
> Not necessarily true.  On x86-64 (non-compat) the fixmap address is in
> kernel space (high bit set), so it can't conflict with anything in
> user space.  On true 32-bit mode, the same applies.  In compat mode,
> the fixed address is in *user* space and might conflict with existing
> uses.
>

The other bit is that the fixmap isn't actually fixed on 32 bits, which 
creates its own set of problems.  As such, I really would prefer a 
properly PIC solution.

	-hpa

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

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