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intel-iommu: Default to non-coherent for domains unattached to iommus
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 <email@example.com> Tested-by: Donald Dutile <firstname.lastname@example.org> Acked-by: Donald Dutile <email@example.com> Acked-by: Chris Wright <firstname.lastname@example.org> Cc: email@example.com Signed-off-by: Joerg Roedel <firstname.lastname@example.org>
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