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

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Date:	Sun, 31 May 2009 00:10:52 +0100
From:	Alan Cox <alan@...rguk.ukuu.org.uk>
To:	Pekka Enberg <penberg@...helsinki.fi>
Cc:	Rik van Riel <riel@...hat.com>, Ingo Molnar <mingo@...e.hu>,
	"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

> It's pretty damn obvious that Larry's patches have a much bigger
> performance impact than using kzfree() for selected parts of the
> kernel. So yes, I do expect him to benchmark and demonstrate that
> kzfree() has _performance problems_ before we can look into merging
> his patches.

We seem to be muddling up multiple things here which is not helpful.

There are three things going on

#1 Is ksize() buggy ?

#2 Using kzfree() to clear specific bits of memory (and I question the
kzfree implementation as it seems ksize can return numbers much much
bigger than the allocated space you need to clear - correct but oversize)
or using other flags. I'd favour kzfree personally (and fixing it to work
properly)

#3 People wanting to be able to select for more security *irrespective*
of performance cost. Which is no different to SELinux for example.

Conflating them all into one mess is causing confusion

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