Re: [RFC KERNEL PATCH v2 2/3] xen/pvh: Unmask irq for passthrough device in PVH dom0

["Roger Pau Monné" <roger.pau@citrix.com>]

On Tue, Dec 12, 2023 at 12:19:49PM +0100, Jan Beulich wrote:
> On 12.12.2023 12:18, Roger Pau Monné wrote:
> > On Tue, Dec 12, 2023 at 10:38:08AM +0100, Jan Beulich wrote:
> >> (I think the Cc list is too long here, but then I don't know who to
> >> keep and who to possibly drop.)
> >>
> >> On 12.12.2023 09:49, Roger Pau Monné wrote:
> >>> On Tue, Dec 12, 2023 at 06:16:43AM +0000, Chen, Jiqian wrote:
> >>>> On 2023/12/11 23:45, Roger Pau Monné wrote:
> >>>>> On Wed, Dec 06, 2023 at 06:07:26AM +0000, Chen, Jiqian wrote:
> >>>>>> +static int xen_pvh_setup_gsi(gsi_info_t *gsi_info)
> >>>>>> +{
> >>>>>> +       struct physdev_setup_gsi setup_gsi;
> >>>>>> +
> >>>>>> +       setup_gsi.gsi = gsi_info->gsi;
> >>>>>> +       setup_gsi.triggering = (gsi_info->trigger == ACPI_EDGE_SENSITIVE ? 0 : 1);
> >>>>>> +       setup_gsi.polarity = (gsi_info->polarity == ACPI_ACTIVE_HIGH ? 0 : 1);
> >>>>>> +
> >>>>>> +       return HYPERVISOR_physdev_op(PHYSDEVOP_setup_gsi, &setup_gsi);
> >>>>>> +}
> >>>>>
> >>>>> Hm, why not simply call pcibios_enable_device() from pciback?  What
> >>>> pcibios_enable_device had been called when using cmd "xl pci-assignable-add sbdf" from pciback. But it didn't do map_pirq and setup_gsi.
> >>>> Because pcibios_enable_device-> pcibios_enable_irq-> __acpi_register_gsi(acpi_register_gsi_ioapic PVH specific)
> >>>>> you are doing here using the hypercalls is a backdoor into what's done
> >>>>> automatically by Xen on IO-APIC accesses by a PVH dom0.
> >>>> But the gsi didn't be unmasked, and vioapic_hwdom_map_gsi is never called.
> >>>> So, I think in pciback, if we can do what vioapic_hwdom_map_gsi does.
> >>>>
> >>>
> >>> I see, it does setup the IO-APIC pin but doesn't unmask it, that's
> >>> what I feared.
> >>>
> >>>>> It will be much more natural for the PVH dom0 model to simply use the
> >>>>> native way to configure and unmask the IO-APIC pin, and that would
> >>>>> correctly setup the triggering/polarity and bind it to dom0 without
> >>>>> requiring the usage of any hypercalls.
> >>>> Do you still prefer that I called unmask_irq in pcistub_init_device, as this v2 patch do?
> >>>> But Thomas Gleixner think it is not suitable to export unmask_irq.
> >>>
> >>> Yeah, that wasn't good.
> >>>
> >>>>>
> >>>>> Is that an issue since in that case the gsi will get mapped and bound
> >>>>> to dom0?
> >>>> Dom0 do map_pirq is to pass the check xc_domain_irq_permission()-> pirq_access_permitted(), 
> >>>
> >>> Can we see about finding another way to fix this check?
> >>>
> >>> One option would be granting permissions over the IRQ in
> >>> PHYSDEVOP_setup_gsi?
> >>
> >> There's no domain available there, and imo it's also the wrong interface to
> >> possibly grant any permissions.
> > 
> > Well, the domain is the caller.
> 
> Granting permission to itself?

See below in the previous email, the issue is not with the
permissions, which are correctly assigned from
dom0_setup_permissions(), but the usage of domain_pirq_to_irq() in
pirq_access_permitted() as called by XEN_DOMCTL_irq_permission.
There's no need to play with the permissions at all.

Regards, Roger.