* Alex Williamson (alex.williamson@xxxxxxxxxx) wrote: > domain_update_iommu_coherency() currently default 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-coherenty, 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 subsequenct attach > of a device makes use of the same dmar domain (now marked coherent) > updates context entries with cohrency enabled, and only disables > coherency as the last step in the process. Specifically, in domain_context_mapping_one(): context_set_translation_type(context, translation); context_set_fault_enable(context); context_set_present(context); domain_flush_cache(domain, context, sizeof(*context)); <-- noop This does not update context entry, leaving IOMMU w/ a non-present context entry, and therefore subsequent DMA generates DMAR faults: DMAR:[DMA Read] Request device [08:10.0] fault addr 37298000 DMAR:[fault reason 02] Present bit in context entry is clear > 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@xxxxxxxxxx> > Tested-by: Donald Dutile <ddutile@xxxxxxxxxx> > Acked-by: Donald Dutile <ddutile@xxxxxxxxxx> Acked-by: Chris Wright <chrisw@xxxxxxxxxxxx> thanks, -chris -- To unsubscribe from this list: send the line "unsubscribe linux-pci" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
