linux-kernel - Re: [PATCH v2 6/7] x86, mm: Support huge I/O mappings on x86

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Message-ID: <1424297657.17007.37.camel@misato.fc.hp.com>
Date:	Wed, 18 Feb 2015 15:14:17 -0700
From:	Toshi Kani <toshi.kani@...com>
To:	Ingo Molnar <mingo@...nel.org>
Cc:	akpm@...ux-foundation.org, hpa@...or.com, tglx@...utronix.de,
	mingo@...hat.com, arnd@...db.de, linux-mm@...ck.org,
	x86@...nel.org, linux-kernel@...r.kernel.org, Elliott@...com
Subject: Re: [PATCH v2 6/7] x86, mm: Support huge I/O mappings on x86

On Wed, 2015-02-18 at 22:57 +0100, Ingo Molnar wrote:
> * Toshi Kani <toshi.kani@...com> wrote:
> 
> > On Wed, 2015-02-18 at 22:15 +0100, Ingo Molnar wrote:
> > > * Toshi Kani <toshi.kani@...com> wrote:
> > > 
> > > > On Wed, 2015-02-18 at 21:44 +0100, Ingo Molnar wrote:
 :
> > 
> > > > [...]  That said, since the patchset also added a new 
> > > > nohugeiomap boot option for the same purpose, I agree 
> > > > that this Kconfig option can be removed.  So, I will 
> > > > remove it in the next version.
> > > > 
> > > > An example of such case is with multiple MTRRs described 
> > > > in patch 0/7.
> > > 
> > > So the multi-MTRR case should probably be detected and 
> > > handled safely?
> > 
> > I considered two options to safely handle this case, i.e. 
> > option A) and B) described in the link below.
> >
> >   https://lkml.org/lkml/2015/2/5/638
> > 
> > I thought about how much complication we should put into 
> > the code for an imaginable platform with a combination of 
> > new NVM (or large I/O range) and legacy MTRRs with 
> > multi-types & contiguous ranges.  My thinking is that we 
> > should go with option C) for simplicity, and implement A) 
> > or B) later if we find it necessary.
> 
> Well, why not option D):
> 
>    D) detect unaligned requests and reject them
> 

That sounds like a good idea!  I will work on it. 

Thanks,
-Toshi


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