linux-kernel - Re: [PATCH v2] x86: Remove compat vdso support

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Message-ID: <531F365B.4060000@linux.intel.com>
Date:	Tue, 11 Mar 2014 09:14:19 -0700
From:	"H. Peter Anvin" <hpa@...ux.intel.com>
To:	Linus Torvalds <torvalds@...ux-foundation.org>,
	Andy Lutomirski <luto@...capital.net>
CC:	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	Stefani Seibold <stefani@...bold.net>,
	the arch/x86 maintainers <x86@...nel.org>,
	Dave Jones <davej@...hat.com>,
	Martin Runge <Martin.Runge@...de-schwarz.com>,
	Andreas Brief <Andreas.Brief@...de-schwarz.com>
Subject: Re: [PATCH v2] x86: Remove compat vdso support

On 03/11/2014 08:30 AM, Linus Torvalds wrote:
> On Tue, Mar 11, 2014 at 7:53 AM, Andy Lutomirski <luto@...capital.net> wrote:
>>
>> I wonder if we can actually detect buggy glibc versions at runtime.
> 
> No, don't do that. That way lies madness.
> 
> What might be acceptable then is to just keep the old config name, and
> if the COMPAT_VDSO config is enabled, you just disable the non-compat
> vdso. At least that way, presumably any opensuse people would have
> their kernel config continue working.
> 
> Then if people have that enabled but didn't  need it, you can enable
> it at runtime with
> 
>     echo 1 > /proc/sys/abi/vsyscall32
> 
> which presumably would need to be exposed on 32-bit kernels too (it
> looks like a x86-64-only thing right now)
> 
> The important thing is that we do *not* break user space. Not ever.
> Not knowingly.
> 

As much as I wouldn't mind getting rid of the compat vdso, I really
don't understand why the trivial solution is being ruled out -- the
trivial solution being to just reserve a little more space in the fixmap
area.

I know Andy wants to move the vdso into a normal vma, which I certainly
support, but it is definitely the non-compat case.

	-hpa


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