On Thu, Jul 11, 2024 at 08:48:10AM -0700, Andrea Bolognani wrote: > IIUC having devices associated to the "correct" SMMU is only a > requirement for optimal performance, not pure functionality, right? > In other words, getting the association wrong will make things slower > but they will keep working.
As part of declaring the iommu as a device libvirt should also specify the iommu capabilities and features. There are capabilities that require perfect 1:1 pIOMMU to vIOMMU matching, or it can't work. For instance if the pIOMMU has a direct path for invalidations then the pIOMMU, pPCI, vIOMMU, and vPCI all must be perfectly matched because the vIOMMU will deliver invalidations directly to a single pIOMMU with no possibility to steer them to the correct place in hypervisor SW. > Is a 1:1 match between pSMMU and vSMMU mandatory? On a system with 4 > SMMUs, could I create a VMs with > > vSMMU0 <-> pSMMU0 > vSMMU1 <-> pSMMU1 > > and another one with > > vSMMU0 <-> pSMMU2 > vSMMU1 <-> pSMMU3 This is fine > assuming of course that devices are assigned to the correct VM? But devices on pSMMU0 cannot be assigned to the second VM in above situations. > How is the association between vSMMU and pSMMU created anyway? Is > that something that the user can control, or is it done automatically > somehow? >From a kernel side VIOMMU will be created in IOMMUFD and it will get as input a reference to a VFIO device. The VIOMMU will be linked to that VFIO device's pIOMMU. Also creating a dummy vIOMMU without any devices and thus no way to reach the pIOMMU is definately "tricky", I'm not sure exactly what is possible there. Jason
