linux-kernel - Re: [patch 0/5] Support for sanitization flag in low-level page allocator

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Date:	Thu, 28 May 2009 11:08:36 +0200
From:	Ingo Molnar <mingo@...e.hu>
To:	Alan Cox <alan@...rguk.ukuu.org.uk>
Cc:	Rik van Riel <riel@...hat.com>,
	"Larry H." <research@...reption.com>, linux-kernel@...r.kernel.org,
	Linus Torvalds <torvalds@...l.org>, linux-mm@...ck.org,
	Ingo Molnar <mingo@...hat.com>, pageexec@...email.hu,
	Linus Torvalds <torvalds@...ux-foundation.org>
Subject: Re: [patch 0/5] Support for sanitization flag in low-level page
	allocator


* Alan Cox <alan@...rguk.ukuu.org.uk> wrote:

> > > As for being swapped out - I do not believe that kernel stacks can 
> > > ever be swapped out in Linux.
> > 
> > yes, i referred to that as an undesirable option - because it slows 
> > down pthread_create() quite substantially.
> > 
> > This needs before/after pthread_create() benchmark results.
> 
> kernel stacks can end up places you don't expect on hypervisor 
> based systems.
> 
> In most respects the benchmarks are pretty irrelevant - wiping 
> stuff has a performance cost, but its the sort of thing you only 
> want to do when you have a security requirement that needs it. At 
> that point the performance is secondary.

Bechmarks, of course, are not irrelevant _at all_.

So i'm asking for this "clear kernel stacks on freeing" aspect to be 
benchmarked thoroughly, as i expect it to have a negative impact - 
otherwise i'm NAK-ing this. Please Cc: me to measurements results.

Thanks,

	Ingo
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