Re: [edk2-devel] [PATCH v2] OvmfPkg/PlatformInitLib: catch QEMU's CPU hotplug reg block regression

["Gerd Hoffmann" <kraxel@redhat.com>]

  Hi,

> >> In particular the firmware makes no further decisions based on
> >> whether QEMU advertized some of these features.
> >
> > I was thinking the other way around:  When cpu hotplug is disabled in
> > qemu it should be safe to skip the whole cpu hotplug checking dance.
> > See test patch below.
> >
> > That would give us a config switch (turn off cpu hotplug support)
> > which would allow edk2 run on qemu versions with broken cpu hotplug.
> >
> > Does the idea look sane or do I miss something?

> This would be wrong.
> 
> [ detailed description snipped here (but stored for later reference,
>   thanks for all the details) ]

So, the tl;dr version:  cpu hotplug is older than smi feature
negotiation, so smi hotplug feature bit being off doesn't imply
qemu wouldn't hotplug cpus.

So, no easy way out.  Luckily this affects tcg only.

For edk2 ci doing (tcg) efi shell test boots switching to Oliver's
latest containers with fixed qemu included should handle things
(latest series just posted).  So once this is in we should be able to
merge this patch without breaking CI.

take care,
  Gerd