linux-kernel - Re: [GIT PULL] xen /proc/mtrr implementation

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Message-ID: <20090518085902.GE10687@elte.hu>
Date:	Mon, 18 May 2009 10:59:02 +0200
From:	Ingo Molnar <mingo@...e.hu>
To:	Jeremy Fitzhardinge <jeremy@...p.org>
Cc:	"Eric W. Biederman" <ebiederm@...ssion.com>,
	Jesse Barnes <jbarnes@...tuousgeek.org>,
	the arch/x86 maintainers <x86@...nel.org>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	Xen-devel <xen-devel@...ts.xensource.com>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	"H. Peter Anvin" <hpa@...or.com>,
	Thomas Gleixner <tglx@...utronix.de>
Subject: Re: [GIT PULL] xen /proc/mtrr implementation

* Jeremy Fitzhardinge <jeremy@...p.org> wrote:

> It's not really virtualized.  We're talking about dom0, which is 
> the guest domain which has access to the real machine's real 
> hardware; the MTRR is part of that.

That is a really broken model and design of virtualization: 
splitting the hypervisor into Xen and then a separate Linux dom0 
entity because reality called home a few years ago and you needed 
actual working drivers and hardware support and a developer 
community to pull that off ...

Here Xen invades an already fragile piece of upstream code 
(/proc/mtrr) that is obsolete and on the way out. If you want a 
solution you should add PAT support to Xen and you should use recent 
upstream kernels. Or you should emulate /proc/mtrr in _Xen the 
hypervisor_, if you really care that much - without increasing the 
amount of crap in Linux.

Without a better reason than what you've given so far the answer is 
really: "no thanks" ...

My suspicion is that Linus would (rightfully) refuse to pull such a 
broken approach from me, so why should i pull it? If i'm wrong and 
if you can get an Acked-by from Linus _before_ sending a pull 
request we can override my NAK. I've Cc:-ed him, in case he wants to 
express an opinion.

	Ingo
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