linux-kernel - Re: [GIT PULL] AMD IOMMU updates for 2.6.28-rc5

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Date:	Thu, 20 Nov 2008 13:25:18 +0900
From:	FUJITA Tomonori <fujita.tomonori@....ntt.co.jp>
To:	muli@...ibm.com
Cc:	fujita.tomonori@....ntt.co.jp, joerg.roedel@....com,
	iommu@...ts.linux-foundation.org, mingo@...hat.com,
	linux-kernel@...r.kernel.org
Subject: Re: [GIT PULL] AMD IOMMU updates for 2.6.28-rc5

On Wed, 19 Nov 2008 14:57:50 +0200
Muli Ben-Yehuda <muli@...ibm.com> wrote:

> > device isolation is not free; e.g. use more memory rather than
> > sharing a protection domain. I guess that more people prefer sharing
> > a protection domain by default.
> 
> I doubt it, why use an isolation-capable IOMMU at all if not for the
> increased reliability? The majority of modern devices---those that you
> are likely to find on machines with an IOMMU---don't have DMA
> limitations.

I guess that there are still some modern SATA HBAs that are not
capable of 64bit DMA. You might be right though.


> > It had been the default option for AMD IOMMU until you hit the
> > bugs. IIRC, VT-d also shares a protection domain by default. It
> > would be nice to avoid surprising users if the two virtualization
> > IOMMUs works in the similar way.
> 
> Calgary has a per-bus protection domain, both on x86 and PPC.

I see. Then it might be better to change VT-d to use a separate
protection domain by default.
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