Re: [XEN PATCH v10 2/5] x86/pvh: Allow (un)map_pirq when dom0 is PVH

[Jan Beulich <jbeulich@suse.com>]

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?

> 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?

> 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.

Jan