linux-kernel - Re: [PATCH 4/5] intel-iommu: Reinstate RMRRs if a device is removed from passthrough domain

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Date:	Tue, 27 Oct 2009 08:15:24 +0000
From:	David Woodhouse <dwmw2@...radead.org>
To:	Alex Williamson <alex.williamson@...com>
Cc:	iommu@...ts.linux-foundation.org, linux-kernel@...r.kernel.org,
	linux-pci@...r.kernel.org
Subject: Re: [PATCH 4/5] intel-iommu: Reinstate RMRRs if a device is
 removed from passthrough domain

On Mon, 2009-10-26 at 17:25 -0600, Alex Williamson wrote:
> When a device is setup for passthrough it has full access to memory
> so processing the RMRRs is unnecessary.  However, if we remove the device
> from the si_domain, we need to reinstate the associated RMRRs.
> 
> Signed-off-by: Alex Williamson <alex.williamson@...com>

If your device is doing DMA to host memory autonomously, you may still
have problems with this patch -- you take it out of the si_domain and
then there's a period of time before you reapply the RMRRs, during which
its DMA may be prevented.

You want to set up the new domain first, then switch the device over to
it atomically.

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

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