On Fri, Sep 27, 2024 at 11:01:41AM -0300, Jason Gunthorpe wrote:
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.
Why would the VM need to know the pSID? The way I view this is quite close to how irq works, the VM only views the GSI which is the virtualized number. The VMM then would need to configure vSID->pSID translation, also without knowing the actual pSID, just how many SIDs are there per-device; very similar to how it configures IRQs through VFIO_DEVICE_GET_INFO/VFIO_DEVICE_SET_IRQS.
And as long as we only allow 1:1 vSID to pSID mapping, I guess it would be easy to implement.
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...
Ah, I thought IOMMUFD would be used instead of VFIO_TYPE1*, which should cover platform devices (VFIO-platform) or am I missing something?
And multi-SIDs is common in platform devices and this would be quite restricting, and I was hoping to support the pKVM vIOMMU through IOMMUFD interface.
If possible, can the UAPI be designed with this in mind, even if not implemented now?
Thanks, Mostafa
Jason