Re: [PATCH] xen/arm: acpi: Support memory reserve configuration table

[Julien Grall <julien@xxxxxxx>]

Hi Leo,

On 25/08/2022 12:50, Leo Yan wrote:
> On Thu, Aug 25, 2022 at 10:07:18AM +0100, Julien Grall wrote:
>
> [...]
>
> > > Xen directly passes ACPI MADT table from UEFI to Linux kernel to Dom0,
> > > (see functions acpi_create_madt() and gic_make_hwdom_madt()), which
> > > means the Linux kernel Dom0 uses the same ACPI table to initialize GICv3
> > > driver, but since Linux kernel Dom0 accesses GIC memory region as IPA,
> > > it still trap to Xen in EL2 for stage 2 translation, so finally Xen
> > > can emulate the GICv3 device for Dom0.
> > In the default setup, dom0 is also the hardware domain. So it owns all of
> > the devices but the ones used by Xen (e.g. interrupt controller, SMMU).
> >
> > Therefore, dom0 will use the same memory layout as the host. At which point,
> > it is a lot more convenient to re-use the host ACPI tables and rewrite only
> > what's necessary.
> We cannot purely talk about interrupt handling without connecting with
> device driver model.
>
> Seems to me, to support para virtualization driver model (like virtio),
> Dom0 needs to provide the device driver backend, and DomUs enables
> the forend device drivers.  In this case, the most hardware interrupts
> (SPIs) are routed to Dom0.
That's correct. Most of the shared interrupts will be routed to dom0.
> To support passthrough driver model (VFIO), Xen needs to configure the
> hardware GICv3 to directly route hardware interrupt to the virtual CPU
> interface.
Do you mean GICv4 rather than GICv3? In the latter, all the interrupts 
will be received in Xen and then routed to the domain by updating the LRs.
> But here I still cannot create the concept that how GIC RD tables play
> roles to support the para virtualization or passthrough mode.
I am not sure what you are actually asking. The pending tables are just 
memory you give to the GICv3 to record the state of the interrupts.
Cheers,

--
Julien Grall