On Mon, Mar 17, 2025 at 04:24:53PM -0300, Jason Gunthorpe wrote: > On Mon, Mar 17, 2025 at 12:10:19PM -0700, Nicolin Chen wrote: > > Another question: how does an emulated device work with a vSMMUv3? > > I could imagine that all the accel steps would be bypassed since > > !sdev->idev. Yet, the emulated iotlb should cache its translation > > so we will need to flush the iotlb, which will increase complexity > > as the TLBI command dispatching function will need to be aware what > > ASID is for emulated device and what is for vfio device.. > > I think you should block it. We already expect different vSMMU's > depending on the physical SMMU under the PCI device, it makes sense > that a SW VFIO device would have it's own, non-accelerated, vSMMU > model in the guest.
Yea, I agree and it'd be cleaner for an implementation separating them. In my mind, the general idea of "accel=on" is also to keep things in a more efficient way: passthrough devices go to HW-accelerated vSMMUs (separated PCIE buses), while emulated ones go to a vSMMU- bypassed (PCIE0). Though I do see the point from QEMU prospective that user may want to start a VM with HW-accelerated vSMMU for one passthrough device using a simple setup without caring about the routing via command. Thanks Nicolin
