On Mon, Mar 24, 2025 at 02:13:20PM +0100, Eric Auger wrote: > >> If VM has an emulated device and a passthrough device: > >> attach the emulated device to PCIE.0 <=> vSMMU bypass (or accel=off?) > >> attach the passthrough device to pxb-pcie <=> vSMMU0 (accel=on) > > This can be other way around as well: > > ie, > > pass-through to pcie.0(accel=on) and emulated to any other pxb-pcie with > > accel = off. > +1 > > > > I think the way bus numbers are allocated in Qemu for pcie.0 and pxb-pcie > > allows > > us to support this in IORT ID maps. > One trouble we may get into is possible bus reordering by the guest. I > don't know the details but I remember that in certain conditions the > guest can reorder the bus numbers.
Hmm, that sounds troublesome. IORT mappings are done using the bus number, which is fixed to a vSMMU. Can we disable that reordering? > Besides what I don't get in the above discussion, related to whether the > accelerated mode can also sipport emulated devices, is that if you use > the originally suggested hierarchy (pxb-pcie + root port + VFIO device) > you eventually get on guest side 2 devices protected by the SMMU > instance: the root port and the VFIO device. They end up in different > iommu groups. So there is already a mix of emulated and VFIO device. Strictly speaking, yes, that's a mix. Maybe we should say emulated endpoints and passthrough endpoints? Thanks Nicolin
