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Date: Thu, 13 Mar 2014 11:21:34 -0700
From: "H. Peter Anvin" <hpa@zytor.com>
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To: Andy Lutomirski <luto@amacapital.net>
CC: Stefani Seibold <stefani@seibold.net>,
        Greg KH <gregkh@linuxfoundation.org>,
        "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
        X86 ML <x86@kernel.org>, Thomas Gleixner <tglx@linutronix.de>,
        Ingo Molnar <mingo@redhat.com>, Andi Kleen <ak@linux.intel.com>,
        Andrea Arcangeli <aarcange@redhat.com>,
        John Stultz <john.stultz@linaro.org>,
        Pavel Emelyanov <xemul@parallels.com>,
        Cyrill Gorcunov <gorcunov@openvz.org>,
        andriy.shevchenko@linux.intel.com,
        Martin Runge <Martin.Runge@rohde-schwarz.com>,
        Andreas Brief <Andreas.Brief@rohde-schwarz.com>,
        Linus Torvalds <torvalds@linux-foundation.org>
Subject: Re: [PATCH 3/3] x86, vdso32: handle 32 bit vDSO larger one page
References: <1394664680-17799-1-git-send-email-stefani@seibold.net> <1394664680-17799-4-git-send-email-stefani@seibold.net> <5320E689.7060607@zytor.com> <CALCETrXQJvkk-5ncSgTyoy9sCN0AT+h9-1F6wAnxqRm242PjrQ@mail.gmail.com> <5321D45C.7040504@zytor.com> <CALCETrVy3oW=qvJWbGtKTZ=0dZLjHtmBphPDnP1N8nLmXc=+9A@mail.gmail.com> <5321F418.1030304@zytor.com>
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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