Re: [RFC XEN PATCH v3 2/3] x86/pvh: Add (un)map_pirq and setup_gsi for PVH dom0

[Jan Beulich <jbeulich@xxxxxxxx>]

On 14.12.2023 23:49, Stefano Stabellini wrote:
> On Thu, 14 Dec 2023, Roger Pau Monné wrote:
>> On Thu, Dec 14, 2023 at 10:58:24AM +0100, Jan Beulich wrote:
>>> On 14.12.2023 10:55, Roger Pau Monné wrote:
>>>> One way to bodge this would be to detect whether the caller of
>>>> XEN_DOMCTL_irq_permission is a PV or an HVM domain, and in case of HVM
>>>> assume the pirq field is a GSI.  I'm unsure however how that will work
>>>> with non-x86 architectures.
> 
> PIRQ is an x86-only concept. We have event channels but no PIRQs on ARM.
> I expect RISC-V will be the same.
> 
> 
>>>> It would  be better to introduce a new XEN_DOMCTL_gsi_permission, or
> 
> "GSI" is another x86-only concept.

Just to mention it - going through the ACPI spec, this looks to be an
arch-neutral ACPI term. It is also used in places which to me look
pretty Arm-centric.

Jan

> So actually the best name was indeed XEN_DOMCTL_irq_permission, given
> that it is using the more arch-neutral "irq" terminology.
> 
> Perhaps it was always a mistake to pass PIRQs to
> XEN_DOMCTL_irq_permission and we should always have passed the real
> interrupt number (GSI on x86, SPI on ARM).
> 
> So your "bodge" is actually kind of OK in my opinion. Basically everyone
> else (x86 HVM/PVH, ARM, RISC-V, probably PPC too) will use
> XEN_DOMCTL_irq_permission with hardware interrupt numbers (GSIs, SPIs,
> etc.), the only special case is x86 PV. It is x86 PV the odd one.
> 
> Given that DOMCTL is an unstable interface anyway, I feel OK making
> changes to it, even better if backward compatible.