linux-kernel - Re: [PATCH 12/12] xen/mtrr: Add mtrr

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Date:	Tue, 28 Sep 2010 15:00:58 +0100
From:	Stefano Stabellini <stefano.stabellini@...citrix.com>
To:	Ingo Molnar <mingo@...e.hu>
CC:	Stefano Stabellini <Stefano.Stabellini@...citrix.com>,
	Thomas Gleixner <tglx@...utronix.de>,
	"H. Peter Anvin" <hpa@...or.com>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"xen-devel@...ts.xensource.com" <xen-devel@...ts.xensource.com>,
	Jeremy Fitzhardinge <Jeremy.Fitzhardinge@...rix.com>,
	"sct@...hat.com" <sct@...hat.com>
Subject: Re: [PATCH 12/12] xen/mtrr: Add mtrr_if support for Xen mtrr

On Tue, 28 Sep 2010, Ingo Molnar wrote:
> 
> * stefano.stabellini@...citrix.com <stefano.stabellini@...citrix.com> wrote:
> 
> > From: Stephen Tweedie <sct@...hat.com>
> > 
> > Add a Xen mtrr type, and reorganise mtrr initialisation slightly to
> > allow the mtrr driver to set up num_var_ranges (Xen needs to do this by
> > querying the hypervisor itself.)
> > 
> > [ Impact: add basic MTRR support ]
> > 
> > Signed-off-by: Stephen Tweedie <sct@...hat.com>
> > Signed-off-by: Jeremy Fitzhardinge <jeremy.fitzhardinge@...rix.com>
> > Signed-off-by: Stefano Stabellini <stefano.stabellini@...citrix.com>
> > ---
> >  arch/x86/kernel/cpu/mtrr/Makefile |    2 +-
> >  arch/x86/kernel/cpu/mtrr/main.c   |    3 +
> >  arch/x86/kernel/cpu/mtrr/mtrr.h   |    7 ++
> >  arch/x86/kernel/cpu/mtrr/xen.c    |  110 +++++++++++++++++++++++++++++++++++++
> >  4 files changed, 121 insertions(+), 1 deletions(-)
> >  create mode 100644 arch/x86/kernel/cpu/mtrr/xen.c
> 
> Still NAK, for the very same reasons as we NAK-ed it the previous time: 
> /proc/mtrr is a problematic and complicated legacy interface that should 
> die. Any modern X server will do the right thing via PAT.
> 

Sorry I should have read the original thread more carefully: I didn't
realize this patch had been NAK-ed.

However it is not a problem because we can easily disable MTRRs from Xen
and with no cpu_has_mtrr the kernel would still boot fine on Xen.
Also I think we do have PAT support nowadays but I'll let Jeremy comment
on that.


> Also, please get the Ack of at least one x86 maintainer for x86 patches.
> 
 
I'll repost the series without the last two patches, so there won't be
any x86 changes at all :)

Many thanks for your quick feedback,

Stefano
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