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

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Date:	Wed, 28 Oct 2009 14:36:59 +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 Tue, 2009-10-27 at 09:50 -0600, Alex Williamson wrote:
> On Tue, 2009-10-27 at 08:15 +0000, David Woodhouse wrote:
> > 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.
> 
> Yes, good point.  I'm not seeing any convenient ways to setup a new
> domain for a device while it's still a member of the si_domain.  It
> looks like I'd need to extract parts of the get_valid_domain_for_dev()
> path and ignore any bits about using the already existing domain.

That seems like a sane plan. That code wants cleaning up anyway, and
factoring out the 'make new domain' part of get_valid_domain_for_dev()
should be simple enough.

-- 
dwmw2

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