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

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Date:	Thu, 13 Mar 2014 12:35:30 -0700
From:	Andy Lutomirski <luto@...capital.net>
To:	Linus Torvalds <torvalds@...ux-foundation.org>
Cc:	Pavel Emelyanov <xemul@...allels.com>,
	Ingo Molnar <mingo@...hat.com>,
	Cyrill Gorcunov <gorcunov@...nvz.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	Stefani Seibold <stefani@...bold.net>,
	Greg KH <gregkh@...uxfoundation.org>,
	"H. Peter Anvin" <hpa@...or.com>,
	Andrea Arcangeli <aarcange@...hat.com>,
	Andreas Brief <Andreas.Brief@...de-schwarz.com>,
	Andi Kleen <ak@...ux.intel.com>,
	John Stultz <john.stultz@...aro.org>,
	Andy Shevchenko <andriy.shevchenko@...ux.intel.com>,
	Thomas Gleixner <tglx@...utronix.de>,
	Martin Runge <Martin.Runge@...de-schwarz.com>,
	"the arch/x86 maintainers" <x86@...nel.org>
Subject: Re: [PATCH 3/3] x86, vdso32: handle 32 bit vDSO larger one page

On Thu, Mar 13, 2014 at 12:21 PM, Linus Torvalds
<torvalds@...ux-foundation.org> wrote:
>
> On Mar 13, 2014 12:13 PM, "Andy Lutomirski" <luto@...capital.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.

I agree.  Also, the syscall instruction selection is currently rather
complicated, and I don't think it can ever be *that* simple :(

>
>> 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".

OK.  I'll send out new patches.

--Andy
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