* Re: [PATCH v2] intel-iommu: Default to non-coherent for domains unattached to iommus
[not found] <20111112002421.10875.8307.stgit@bling.home>
@ 2012-09-18 11:58 ` Joerg Roedel
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From: Joerg Roedel @ 2012-09-18 11:58 UTC (permalink / raw)
To: Alex Williamson; +Cc: dwmw2, linux-pci, linux-kernel, chrisw, iommu
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@redhat.com>
> Tested-by: Donald Dutile <ddutile@redhat.com>
> Acked-by: Donald Dutile <ddutile@redhat.com>
> Acked-by: Chris Wright <chrisw@sous-sol.org>
Applied, thanks.
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