linux-kernel - Re: [PATCH 3/3] x86, vdso32: handle 32 bit vDSO larger one page

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Message-ID: <5321F72E.7030109@zytor.com>
Date:	Thu, 13 Mar 2014 11:21:34 -0700
From:	"H. Peter Anvin" <hpa@...or.com>
To:	Andy Lutomirski <luto@...capital.net>
CC:	Stefani Seibold <stefani@...bold.net>,
	Greg KH <gregkh@...uxfoundation.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	X86 ML <x86@...nel.org>, Thomas Gleixner <tglx@...utronix.de>,
	Ingo Molnar <mingo@...hat.com>,
	Andi Kleen <ak@...ux.intel.com>,
	Andrea Arcangeli <aarcange@...hat.com>,
	John Stultz <john.stultz@...aro.org>,
	Pavel Emelyanov <xemul@...allels.com>,
	Cyrill Gorcunov <gorcunov@...nvz.org>,
	andriy.shevchenko@...ux.intel.com,
	Martin Runge <Martin.Runge@...de-schwarz.com>,
	Andreas Brief <Andreas.Brief@...de-schwarz.com>,
	Linus Torvalds <torvalds@...ux-foundation.org>
Subject: Re: [PATCH 3/3] x86, vdso32: handle 32 bit vDSO larger one page

On 03/13/2014 11:08 AM, H. Peter Anvin wrote:
> On 03/13/2014 10:28 AM, Andy Lutomirski wrote:
>>
>> Does this mean you prefer the relocation approach to the compat vdso
>> removal approach?  It seems like Linus is okay with either one.
>>
> 
> Actually, thinking about it, removing it is probably better:
> 
> a) gets rid of legacy code, making room for unification;
> b) either way enabling compat support (either relocation or disabling
>    the vdso) has a performance penalty for *all* processes.
> 
> The only way to avoid that is to have a vdso at a fixed addresses across
> all processes, either in the fixmap or in the user area (presumably at
> the very top.)
> 

So going back and re-reading all the threads, the consensus was to
remove the compat vdso, but recycling the CONFIG_COMPAT_VDSO
configuration option name for the default-disable option.

It is important that anyone who actually cares about performance unsets
the option.

	-hpa


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