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
