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Date: Tue, 11 Mar 2014 09:14:19 -0700
From: "H. Peter Anvin" <hpa@linux.intel.com>
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To: Linus Torvalds <torvalds@linux-foundation.org>,
        Andy Lutomirski <luto@amacapital.net>
CC: "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
        Stefani Seibold <stefani@seibold.net>,
        the arch/x86 maintainers <x86@kernel.org>,
        Dave Jones <davej@redhat.com>,
        Martin Runge <Martin.Runge@rohde-schwarz.com>,
        Andreas Brief <Andreas.Brief@rohde-schwarz.com>
Subject: Re: [PATCH v2] x86: Remove compat vdso support
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On 03/11/2014 08:30 AM, Linus Torvalds wrote:
> On Tue, Mar 11, 2014 at 7:53 AM, Andy Lutomirski <luto@amacapital.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