On 30/08/2018 05:09, Lu Baolu wrote:
Below APIs are introduced in the IOMMU glue for device drivers to use
the finer granularity translation.
- Represents the ability for supporting multiple domains per device
(a.k.a. finer granularity translations) of the IOMMU hardware.
iommu_capable() cannot represent hardware capabilities, we need
something else for systems with multiple IOMMUs that have different
caps. How about iommu_domain_get_attr on the device's domain instead?
* iommu_en(dis)able_aux_domain(struct device *dev)
- Enable/disable the multiple domains capability for a device
referenced by @dev.
* iommu_auxiliary_id(struct iommu_domain *domain)
- Return the index value used for finer-granularity DMA translation.
The specific device driver needs to feed the hardware with this
value, so that hardware device could issue the DMA transaction with
this value tagged.
This could also reuse iommu_domain_get_attr.
More generally I'm having trouble understanding how auxiliary domains
will be used. So VFIO allocates PASIDs like this:
* iommu_domain_alloc() -> dom1
* iommu_domain_alloc() -> dom2
* iommu_attach_device(dom1, parent_dev)
-> dom1 gets PASID #1
* iommu_attach_device(dom2, parent_dev)
-> dom2 gets PASID #2
Then I'm not sure about the next steps, when userspace does
VFIO_IOMMU_MAP_DMA or VFIO_IOMMU_BIND on an mdev's container. Is the
following use accurate?
For the single translation level:
* iommu_map(dom1, ...) updates first-level/second-level pgtables for
* iommu_map(dom2, ...) updates first-level/second-level pgtables for
* iommu_map(dom1, ...) updates second-level pgtables for PASID #1
* iommu_bind_table(dom1, ...) binds first-level pgtables, provided by
the guest, for PASID #1
* iommu_map(dom2, ...) updates second-level pgtables for PASID #2
* iommu_bind_table(dom2, ...) binds first-level pgtables for PASID #2
I'm trying to understand how to implement this with SMMU and other
IOMMUs. It's not a clean fit since we have a single domain to hold the
Then again, the nested case probably doesn't
matter for us - we might as well assign the parent directly, since all
mdevs have the same second-level and can only be assigned to the same VM.
Also, can non-VFIO device drivers use auxiliary domains to do map/unmap
on PASIDs? They are asking to do that and I'm proposing the private
PASID thing, but since aux domains provide a similar feature we should
probably converge somehow.