linux-kernel - Re: [PATCH] xen: core dom0 support

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Message-ID: <49B441D9.4010004@zytor.com>
Date:	Sun, 08 Mar 2009 15:08:25 -0700
From:	"H. Peter Anvin" <hpa@...or.com>
To:	Ingo Molnar <mingo@...e.hu>
CC:	Jeremy Fitzhardinge <jeremy@...p.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	the arch/x86 maintainers <x86@...nel.org>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	Xen-devel <xen-devel@...ts.xensource.com>
Subject: Re: [PATCH] xen: core dom0 support

Ingo Molnar wrote:
> 
> Since it's the same kernel image i think the only truly reliable 
> method would be to reboot between _different_ kernel images: 
> same instructions but randomly re-align variables both in terms 
> of absolute address and in terms of relative position to each 
> other. Plus randomize bootmem allocs and never-gets-freed-really 
> boot-time allocations.
> 
> Really hard to do i think ...
> 

Ouch, yeah.

On the other hand, the numbers made sense to me, so I don't see why
there is any reason to distrust them.  They show a 5% overhead with
pv_ops enabled, reduced to a 2% overhead with the changed.  That is more
or less what would match my intuition from seeing the code.

	-hpa

-- 
H. Peter Anvin, Intel Open Source Technology Center
I work for Intel.  I don't speak on their behalf.

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