Re: [PATCH v4 0/3] hw/riscv/virt: pflash improvements

[Andrew Jones]

On Fri, May 26, 2023 at 03:49:11AM -0400, Andrea Bolognani wrote:
> On Fri, May 26, 2023 at 08:39:07AM +0200, Andrew Jones wrote:
> > On Thu, May 25, 2023 at 11:03:52AM -0700, Andrea Bolognani wrote:
> > > With these patches applied, libvirt built from the master branch,
> > > edk2 built from your branch and a JSON firmware descriptor for it
> > > installed (attached), it's finally possible to boot an unmodified
> > > openSUSE Tumbleweed RISC-V disk image by simply including
> > >
> > >   <os firmware='efi'>
> >
> > Hi Andrea,
> >
> > I'm a bit concerned that we don't also need to add some XML in order to
> > disable ACPI right now. RISC-V guest kernels will support ACPI in the
> > near future. Ideally a default libvirt VM using edk2 will also use ACPI.
> > Will there be a problem with changing that default later? If so, then
> > I'd change it now and continue burdening developers a bit longer by
> > requiring them to explicitly disable it.
> 
> libvirt doesn't enable ACPI by default on any architecture, not even
> x86_64. virt-manager will enable it by default if it's advertised as
> available on the architecture in the capabilities XML.
> 
> However, it looks like the corresponding code in libvirt is not as
> dynamic as I would have assumed: instead, we hardcode the list of
> architectures that advertise ACPI support available, and at the
> moment that list does *not* include RISC-V :)
> 
> I think it would make sense to fix this, but I want to make sure I
> understand the impact. Is this just an UEFI thing? All my other
> RISC-V guests (Fedora, Ubuntu, FreeBSD) boot just fine when I turn
> ACPI on. In fact, even the openSUSE one works with ACPI on, as long
> as the UEFI implementation used is the U-Boot one rather than edk2.
> 
> So, are edk2 users the only ones who would (temporarily) need to
> manually turn ACPI off if virt-manager started enabling it by
> default?

I assume so, but I'm not tracking firmware status. If the firmware
doesn't extract the ACPI tables from QEMU and present them to the
guest (afaik only edk2 does that), then the guest kernel falls back
to DT, which is why it's working for you.

I suppose we should wait until Linux merges the ACPI patches, before
adding RISC-V to the libvirt capabilities ACPI list. Then, is it
possible to use something like libosinfo to inform virt-manager
when it should enable ACPI and when not? Later distro images, with
later kernels, will want to use ACPI by default, but older images
will still need to use DT.

Thanks,
drew