Re: [PATCH v2 06/19] iommufd/viommu: Add IOMMU_VIOMMU_SET/UNSET_VDEV_ID ioctl

On Fri, Sep 27, 2024 at 01:50:52PM +0000, Mostafa Saleh wrote:

My understanding of IOMMUFD is very little, but AFAICT, that means that
it’s assumed that each device can only have one stream ID(RID)?

As I can see in patch 17 in arm_smmu_convert_viommu_vdev_id(), it
converts the virtual ID to a physical one using master->streams[0].id.

Is that correct or am I missing something?

As I am looking at similar problem for paravirtual IOMMU with pKVM, where
the UAPI would be something similar to:

	GET_NUM_END_POINTS(dev) => nr_sids

	SET_END_POINT_VSID(dev, sid_index, vsid)

Similar to what VFIO does with IRQs.

As a device can have many SIDs.

We don't support multi SID through this interface, at least in this
version.

To do multi-sid you have to inform the VM of all the different pSIDs
the device has and then setup the vSID/pSID translation to map them
all to the HW invalidation logic.

Which is alot more steps, and we have no use case right now. Multi-sid
is also not something I expect to see in any modern PCI device, and
this is VFIO PCI...

Jason