Re: [XEN PATCH v12 4/7] x86/domctl: Add hypercall to set the access of x86 gsi

[Roger Pau Monné <roger.pau@xxxxxxxxxx>]

On Mon, Jul 08, 2024 at 07:41:21PM +0800, Jiqian Chen wrote:
> Some type of domains don't have PIRQs, like PVH, it doesn't do
> PHYSDEVOP_map_pirq for each gsi. When passthrough a device
> to guest base on PVH dom0, callstack
> pci_add_dm_done->XEN_DOMCTL_irq_permission will fail at function
> domain_pirq_to_irq, because PVH has no mapping of gsi, pirq and
> irq on Xen side.
> What's more, current hypercall XEN_DOMCTL_irq_permission requires
> passing in pirq to set the access of irq, it is not suitable for
> dom0 that doesn't have PIRQs.
> 
> So, add a new hypercall XEN_DOMCTL_gsi_permission to grant/deny
> the permission of irq(translate from x86 gsi) to dumU when dom0
> has no PIRQs.

I've been wondering about this, and if the hypercall is strictly to
resolve GSIs into IRQs, isn't that the case that Xen identity maps GSI
into the IRQ space, and hence no translation is required?

Thanks, Roger.