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Subject: Re: [PATCH 3/3] x86, vdso32: handle 32 bit vDSO larger one page
From: "H. Peter Anvin" <hpa@zytor.com>
Date: Thu, 13 Mar 2014 12:33:49 -0700
To: Linus Torvalds <torvalds@linux-foundation.org>,
        Andy Lutomirski <luto@amacapital.net>
CC: Pavel Emelyanov <xemul@parallels.com>, Ingo Molnar <mingo@redhat.com>,
        Cyrill Gorcunov <gorcunov@openvz.org>,
        "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
        Stefani Seibold <stefani@seibold.net>,
        Greg KH <gregkh@linuxfoundation.org>,
        Andrea Arcangeli <aarcange@redhat.com>,
        Andreas Brief <Andreas.Brief@rohde-schwarz.com>,
        Andi Kleen <ak@linux.intel.com>, John Stultz <john.stultz@linaro.org>,
        Andy Shevchenko <andriy.shevchenko@linux.intel.com>,
        Thomas Gleixner <tglx@linutronix.de>,
        Martin Runge <Martin.Runge@rohde-schwarz.com>,
        the arch/x86 maintainers <x86@kernel.org>
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If we have to stick anything in the fixmap it might add well be the real vdso...

On March 13, 2014 12:21:54 PM PDT, Linus Torvalds <torvalds@linux-foundation.org> wrote:
>On Mar 13, 2014 12:13 PM, "Andy Lutomirski" <luto@amacapital.net>
>wrote:
>>
>> How?  We either set null in AT_SYSINFO_EHDR, we set something simple
>> that SuSE is okay with (and compile separate images?) or we set
>> something fancy and not relocated, and SuSE crashes.
>
>Yeah, I was thinking that "something simple is the fixmap space that
>suse
>would be happy with"
>
>Keyword being "simple", ie so simple that it's not a maintenance
>headache
>even if it's different from the "real" vdso.
>
>But I suspect we don't really need it.
>
>> On a related note: is it okay to keep the option called
>> CONFIG_COMPAT_VDSO but change the default to n?
>
>Yes. If you start from scratch with a config, you have to get the
>options
>right. It's just the "I upgraded the kernel, did an oldconfig, and it
>doesn't work" case that we should avoid.
>
>The alternative would be to make a new config name, but then it has to
>default to the compatible state (iow no vdso at all by default),
>because
>that's the rule: make oldconfig should work for people.
>
>Basically, kernel upgrades should be nobrainers and "just work".
>
>     Linus

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