Re: roms/SLOF: crashes on G5 (970) with newer pseries

[Jake Hamby]

Sorry, I'll have to get more info on the SLOF problem. I'll report
back when I do.

There are some more interesting/blocking issues I've been working on
related to KVM-PR bugs that affect larger numbers of people, but I'll
write a separate email for those.

Thanks all,
Jake

On Thu, Apr 15, 2021 at 1:36 AM Alexey Kardashevskiy <aik@ozlabs.ru> wrote:
>
>
>
> On 13/04/2021 02:42, Jake Hamby wrote:
> > I've been testing QEMU + KVM-PR on a Power Mac G5 Quad, and it runs
> > better than I expected, but with a few glitches. The first one I
> > discovered: the SLOF ROM has been compiled for POWER7 or newer, and it
> > crashes when run on a G5 (KVM and TCG) if the pseries version is set
> > to 2.6 or higher. The xHCI SLOF driver crashes the guest with
> > pseries-2.6, and it doesn't even get to initializing the screen with
> > higher versions.
>
>
> Try
> https://patchwork.ozlabs.org/project/slof/patch/20200721131351.106014-1-lvivier@redhat.com/
> for xhci.
>
>
> > Fortunately, it was a small change to recompile SLOF from source with
> > the target set to "ppc970" instead of "ppcp7". I had to fix a few
> > build errors first. Commit link (I would paste the patches inline, but
> > I don't have Gmail set up for that yet):
> >
> > https://github.com/jhamby/SLOF/commit/4ae9a012a2cec4a1b476c1b4a3933def5ae36f2b
>
> Have register dump of the crash? Since pseries prior to 2.6 worked and
> it is -DCPU_PPCP7 since ever, it does not sound like P7 is the problem here.
>
>
> >
> > And my commit to change the default QEMU board type to ppc970:
> >
> > https://github.com/jhamby/SLOF/commit/619539cfa3a37f9527ae382cdb7573de7fa6d836
> >
> > With these changes, the compiled slof.bin works perfectly for me with
> > pseries versions up to 4.2 (the highest version I tried that doesn't
> > expect CPU capabilities that the G5 doesn't have) and the 970mp CPU
> > type (with both KVM-PR and TCG).
>
> What are these missing capabilities? This should not change across QEMU
> versions, I am a bit surprised.
>
> > I don't know if there are any negative performance implications of
> > compiling SLOF for PPC 970 and using it with later CPU types, but I'm
> > guessing that PowerNV is the preferred machine type for POWER8 and
> > newer now. It does feel like a bug that the SLOF ROM crashes
> > unexpectedly with older CPU models in legal machine configurations.
>
> The pseries machine is still preferred as this is the only machine type
> capable of running under KVM. The powernv machine is fully emulated and
> is not fast as all.
>
>
>
> --
> Alexey