On 2024/6/17 22:45, Jan Beulich wrote: > On 17.06.2024 11:00, Jiqian Chen wrote: >> If run Xen with PVH dom0 and hvm domU, hvm will map a pirq for >> a passthrough device by using gsi, see qemu code >> xen_pt_realize->xc_physdev_map_pirq and libxl code >> pci_add_dm_done->xc_physdev_map_pirq. Then xc_physdev_map_pirq >> will call into Xen, but in hvm_physdev_op, PHYSDEVOP_map_pirq >> is not allowed because currd is PVH dom0 and PVH has no >> X86_EMU_USE_PIRQ flag, it will fail at has_pirq check. >> >> So, allow PHYSDEVOP_map_pirq when dom0 is PVH and also allow >> PHYSDEVOP_unmap_pirq for the failed path to unmap pirq. > > Why "failed path"? Isn't unmapping also part of normal device removal > from a guest? Yes, both. I will change to also "allow PHYSDEVOP_unmap_pirq for the device removal path to unmap pirq".
> >> And >> add a new check to prevent self map when subject domain has no >> PIRQ flag. > > You still talk of only self mapping, and the code also still does only > that. As pointed out before: Why would you allow mapping into a PVH > DomU? IOW what purpose do the "d == currd" checks have? The checking I added has two purpose, first is I need to allow this case: Dom0(without PIRQ) + DomU(with PIRQ), because the original code just do (!has_pirq(currd)) will cause map_pirq fail in this case. Second I need to disallow self-mapping: DomU(without PIRQ) do map_pirq, the "d==currd" means the currd is the subject domain itself. Emmm, I think I know what's your concern. Do you mean I need to " Prevent map_pirq when currd has no X86_EMU_USE_PIRQ flag " instead of " Prevent self-map when currd has no X86_EMU_USE_PIRQ flag ", so I need to remove "d==currd", right? > >> So that domU with PIRQ flag can success to map pirq for >> passthrough devices even dom0 has no PIRQ flag. > > There's still a description problem here. Much like the first sentence, > this last one also says that the guest would itself map the pIRQ. In > which case there would still not be any reason to expose the sub- > functions to Dom0. If change to " So that the interrupt of a passthrough device can success to be mapped to pirq for domU with PIRQ flag when dom0 is PVH.", Is it OK? > > Jan -- Best regards, Jiqian Chen.
