linux-kernel - Re: [PATCH v2] intel-iommu: Default to non-coherent for domains unattached to iommus

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Message-ID: <20120918115802.GJ2505@amd.com>
Date:	Tue, 18 Sep 2012 13:58:02 +0200
From:	Joerg Roedel <joerg.roedel@....com>
To:	Alex Williamson <alex.williamson@...hat.com>
CC:	<dwmw2@...radead.org>, <linux-pci@...r.kernel.org>,
	<linux-kernel@...r.kernel.org>, <chrisw@...s-sol.org>,
	<iommu@...ts.linux-foundation.org>
Subject: Re: [PATCH v2] intel-iommu: Default to non-coherent for domains
 unattached to iommus

On Fri, Nov 11, 2011 at 05:26:44PM -0700, Alex Williamson wrote:
> domain_update_iommu_coherency() currently defaults to setting domains
> as coherent when the domain is not attached to any iommus.  This
> allows for a window in domain_context_mapping_one() where such a
> domain can update context entries non-coherently, and only after
> update the domain capability to clear iommu_coherency.
> 
> This can be seen using KVM device assignment on VT-d systems that
> do not support coherency in the ecap register.  When a device is
> added to a guest, a domain is created (iommu_coherency = 0), the
> device is attached, and ranges are mapped.  If we then hot unplug
> the device, the coherency is updated and set to the default (1)
> since no iommus are attached to the domain.  A subsequent attach
> of a device makes use of the same dmar domain (now marked coherent)
> updates context entries with coherency enabled, and only disables
> coherency as the last step in the process.
> 
> To fix this, switch domain_update_iommu_coherency() to use the
> safer, non-coherent default for domains not attached to iommus.
> 
> Signed-off-by: Alex Williamson <alex.williamson@...hat.com>
> Tested-by: Donald Dutile <ddutile@...hat.com>
> Acked-by: Donald Dutile <ddutile@...hat.com>
> Acked-by: Chris Wright <chrisw@...s-sol.org>

Applied, thanks.

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