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

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Message-ID: <02122083.20100928151928@eikelenboom.it>
Date:	Tue, 28 Sep 2010 15:19:28 +0200
From:	Sander Eikelenboom <linux@...elenboom.it>
To:	mingo@...hat.com, Jeremy Fitzhardinge <jeremy@...p.org>,
	Stefano Stabellini <stefano.stabellini@...citrix.com>
CC:	linux-kernel@...r.kernel.org,
	"xen-devel@...ts.xensource.com" <xen-devel@...ts.xensource.com>,
	<x86@...nel.org>
Subject: Re: [PATCH 12/12] xen/mtrr: Add mtrr_if support for Xen mtrr

>* stefano.stabellini@...xxxxxxxxxx <stefano.stabellini@...xxxxxxxxxx> wrote:
>
>> From: Stephen Tweedie <sct@...xxxxxxx>
>> 
>> 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@...xxxxxxx>
>> Signed-off-by: Jeremy Fitzhardinge <jeremy.fitzhardinge@...xxxxxxx>
>> Signed-off-by: Stefano Stabellini <stefano.stabellini@...xxxxxxxxxx>
>> ---
>> 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.
>
>Also, please get the Ack of at least one x86 maintainer for x86 patches.
>
>Thanks,
>
>Ingo
>--
>

I can't find the MTRR API to be officially deprecated with any schedule for removal (at least i couldn't find it in feature-removal-schedule.txt).
KVM has had patches for MTRR as well, if it's so deprecated .. why has it ? .. legacy support for a not officially deprecated API perhaps ? To support CPU's that support MTRR but not PAT ?

If you think the MTRR interface should die, and should die fast, why hasn't it been added to feature-removal-schedule.txt for a complete removal in a not so distant future, since this is the only way to force all users to switch to PAT.

Perhaps it would be fair to ask for a working PAT implementation besides MTRR, but since it is not officially deprecated completely objecting a MTRR one just for Xen seems a bit unfair to me.

--
Sander

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