linux-kernel - Re: [PATCH v5 8/9] x86-64: Emulate legacy vsyscalls

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Date:	Wed, 8 Jun 2011 12:39:06 +0200
From:	Ingo Molnar <mingo@...e.hu>
To:	pageexec@...email.hu
Cc:	Andi Kleen <andi@...stfloor.org>, Andrew Lutomirski <luto@....edu>,
	x86@...nel.org, Thomas Gleixner <tglx@...utronix.de>,
	linux-kernel@...r.kernel.org, Jesper Juhl <jj@...osbits.net>,
	Borislav Petkov <bp@...en8.de>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Arjan van de Ven <arjan@...radead.org>,
	Jan Beulich <JBeulich@...ell.com>,
	richard -rw- weinberger <richard.weinberger@...il.com>,
	Mikael Pettersson <mikpe@...uu.se>,
	Brian Gerst <brgerst@...il.com>,
	Louis Rilling <Louis.Rilling@...labs.com>,
	Valdis.Kletnieks@...edu
Subject: Re: [PATCH v5 8/9] x86-64: Emulate legacy vsyscalls


* pageexec@...email.hu <pageexec@...email.hu> wrote:

> On 8 Jun 2011 at 12:06, Andi Kleen wrote:
> 
> > > eventually may even go away as time progresses and linux 
> > > systems begin to fully rely on the vdso instead.
> > 
> > That assumes that everyone uses glibc and also updates their 
> > userland. As pointed out many times that's a deeply flawed 
> > assumption.
> 
> i think the assumption is not that everyone uses glibc but that 
> everyone else (as in, every other libc) can simply take the 
> necessary changes from glibc, provided they need such changes at 
> all (i.e., they're using the vsyscall entry points over the vdso 
> ones).
> 
> i frankly didn't check any of the alternatives myself 
> (uclibc/klibc/bionic/etc) but i can't imagine that it'd be that 
> much harder to patch them than glibc.

Correct. Also, as i pointed it out in the previous mail, ABI does not 
mean 'will execute the same instructions', that would be silly. We 
*do* fix serious wide-scale performance regressions (obviously), but 
if it's about some weird crazy legacy path that we had good security 
reasons to change, and which is trivial to performance-improve in the 
library then we are well within our boundaries to keep the change.

> as i said, this was a compromise solution but then i think you 
> already made it clear that you didn't even think there was a 
> problem here to solve, so i guess we should work that out first, if 
> you want to ;).

Heh, indeed ;-)

Thanks,

	Ingo
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