Subject: Re: [PATCH 4/5] intel-iommu: Reinstate RMRRs if a device is
 removed from passthrough domain
From: Alex Williamson <alex.williamson@hp.com>
To: David Woodhouse <dwmw2@infradead.org>
Cc: iommu@lists.linux-foundation.org, linux-kernel@vger.kernel.org,
       linux-pci@vger.kernel.org
In-Reply-To: <1256631324.9814.14.camel@macbook.infradead.org>
References: <20091026232401.9646.90540.stgit@nehalem.aw>
	 <20091026232514.9646.58322.stgit@nehalem.aw>
	 <1256631324.9814.14.camel@macbook.infradead.org>
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Organization: HP OSLO R&D
Date: Tue, 27 Oct 2009 09:50:32 -0600
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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@hp.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.  Is
there an easier way?  Thanks,

Alex


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