linux-kernel - Re: [RFC v6][PATCH 4/4] intel_txt: force IOMMU on for Intel(R) TXT launch

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Message-ID: <20090705202316.GH17910@elf.ucw.cz>
Date:	Sun, 5 Jul 2009 22:23:16 +0200
From:	Pavel Machek <pavel@....cz>
To:	Ingo Molnar <mingo@...e.hu>
Cc:	Joseph Cihula <joseph.cihula@...el.com>,
	linux-kernel@...r.kernel.org, arjan@...ux.intel.com, hpa@...or.com,
	andi@...stfloor.org, chrisw@...s-sol.org, jmorris@...ei.org,
	jbeulich@...ell.com, peterm@...hat.com, gang.wei@...el.com,
	shane.wang@...el.com
Subject: Re: [RFC v6][PATCH 4/4] intel_txt: force IOMMU on for Intel(R) TXT
	launch

On Fri 2009-07-03 10:21:11, Ingo Molnar wrote:
> 
> * Pavel Machek <pavel@....cz> wrote:
> 
> > 
> > On Tue 2009-06-30 19:31:10, Joseph Cihula wrote:
> > > The tboot module will DMA protect all of memory in order to ensure the that
> > > kernel will be able to initialize without compromise (from DMA).  Consequently,
> > > the kernel must enable Intel(R) Virtualization Technology for Directed I/O
> > > (VT-d or Intel IOMMU) in order to replace this broad protection with the
> > > appropriate page-granular protection.  Otherwise DMA devices will be unable
> > > to read or write from memory and the kernel will eventually panic.
> > > 
> > > Because runtime IOMMU support is configurable by command line options, this
> > > patch will force it to be enabled regardless of the options specified, and will
> > > log a message if it was required to force it on.
> > > 
> > > 
> > >  dmar.c        |    7 +++++++
> > >  intel-iommu.c |   17 +++++++++++++++--
> > >  2 files changed, 22 insertions(+), 2 deletions(-)
> > > 
> > > Signed-off-by: Joseph Cihula <joseph.cihula@...el.com>
> > > Signed-off-by: Shane Wang <shane.wang@...el.com>
> > 
> > NAK. Breaks user expectations, misses  docs updates. 
> 
> What's your proposed solution? If an incompatible IOMMU option is 
> specified should the kernel to disable TXT and panic?

Yes.

...and whether we decide one way or another, it needs to be documented.a

											Pavel
-- 
(english) http://www.livejournal.com/~pavelmachek
(cesky, pictures) http://atrey.karlin.mff.cuni.cz/~pavel/picture/horses/blog.html
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