linux-kernel - Re: [PATCH v2] IA64 Compilation Error Fix for Intel IOMMU Identity Mapping Support

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Message-Id: <1246103049.663.437.camel@macbook.infradead.org>
Date:	Sat, 27 Jun 2009 12:44:09 +0100
From:	David Woodhouse <dwmw2@...radead.org>
To:	Linus Torvalds <torvalds@...ux-foundation.org>
Cc:	Chris Wright <chrisw@...hat.com>,
	FUJITA Tomonori <fujita.tomonori@....ntt.co.jp>,
	fenghua.yu@...el.com, akpm@...ux-foundation.org,
	tony.luck@...el.com, linux-kernel@...r.kernel.org,
	iommu@...ts.linux-foundation.org, linux-ia64@...r.kernel.org
Subject: Re: [PATCH v2] IA64 Compilation Error Fix for Intel IOMMU Identity
 Mapping Support

On Thu, 2009-06-25 at 19:00 -0700, Linus Torvalds wrote:
> 
> On Thu, 25 Jun 2009, Chris Wright wrote:
> > I tested it on x86; works fine and creates a slightly tighter set of page
> > tables (matching to e820).  But I don't have an IA-64 box w/ an IOMMU.
> > 
> > It does have one problem, however, the graphics work around code isn't
> > compiled in on IA-64, so it needs:
> 
> Ok. Sounds like what I want is to get this patch through the ia64 people, 
> after it has gotten some testing there. Since ia64 is where the current 
> kernel fails anyway, that sounds like the motivation will be there too.
> 
> And there's little point in me merging it until it's been tested to fix 
> the actual problem we have now.

Well, the main problem is that the kernel doesn't build -- and it _has_
been tested to fix that.

As long as the daily linux-next test builds work, nobody really seems to
_care_ about VT-d on IA64 -- certainly not enough to get me a box when
they asked me to become VT-d maintainer.

Now that I chase it up, I've received only one test report and that was
"oh, even 2.6.29 doesn't boot on this box with VT-d enabled".

The patch _does_ fix the build breakage, definitely seems to be doing
the right thing, and the worst case is that the new feature doesn't work
on IA64. So I think we should merge it.

I'll bash some heads together and try to get myself some hardware so I
can actually test it on IA64 -- it looks like we have more problems
there than the small possibility that the new passthrough feature might
do the wrong thing (and in fact I suspect all IA64 VT-d hardware is new
enough to have the _hardware_ passthrough anyway, so won't need this
identity mapping set up at all).

Please pull Chris's fix from
	git://git.infradead.org/iommu-2.6.git

-- 
David Woodhouse                            Open Source Technology Centre
David.Woodhouse@...el.com                              Intel Corporation

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