Re: QEMU features useful for Xen development?

[Peter Maydell <peter.maydell@xxxxxxxxxx>]

On Thu, 31 Aug 2023 at 01:57, Stefano Stabellini <sstabellini@xxxxxxxxxx> wrote:
> As Xen is gaining R52 and R82 support, it would be great to be able to
> use QEMU for development and testing there as well, but I don't think
> QEMU can emulate EL2 properly for the Cortex-R architecture. We would
> need EL2 support in the GIC/timer for R52/R82 as well.

We do actually have a Cortex-R52 model which at least in theory
should include EL2 support, though as usual with newer QEMU
stuff it quite likely has lurking bugs; I'm not sure how much
testing it's had. Also there is currently no board model which
will work with the Cortex-R52 so it's a bit tricky to use in practice.
(What sort of board model would Xen want to use it with?)

The Cortex-R82 would be more work, because (unlike the R52) it's
AArch64, and we don't have Armv8-R AArch64 support yet, only the AArch32.

I haven't looked at whether GIC on R-profile requires any changes
from the A-profile GIC; on A-profile obviously we emulate the
virtualization support already.

> On Cortex-As, in addition to a PCI root complex and an arbitrary PCI
> device, SMMUv3 emulation (both stages) and GICv3 ITS are needed to be
> able to test PCI Passthrough. However, if I recall correctly SMMUv3
> emulation in QEMU might not be complete enough to enable us to use it.

Yeah, at the moment the SMMU emulation supports stage 1 and stage 2,
but not both at the same time. This is good enough for PCI passthrough
with a Linux guest using KVM to pass a device through to a nested
Linux guest.

thanks
-- PMM