Re: [XEN PATCH] x86/ACPI: Ignore entries with invalid APIC IDs when parsing MADT

[Thomas Gleixner <tglx@linutronix.de>]

On Mon, Sep 11 2023 at 19:24, Andrew Cooper wrote:
> Furthermore, cursory testing that Thomas did for the Linux topology work
> demonstrates that it is broken anyway for reasons unrelated to ACPI parsing.
>
> Even furthermore, it's an area of the Xen / dom0 boundary which is
> fundamentally broken for non-PV cases, and undocumented for the PV case,
> hence why it's broken in Linux.
>
> Physical CPU Hotplug does not pass the bar for being anything more than
> experimental.  It's absolutely not tech-preview level because the only
> demo it has had in an environment (admittedly virtual) which does
> implement the spec in a usable way demonstrates that it doesn't function.
>
> The fact no-one has noticed until now shows that the feature isn't used,
> which comes back around full circle to the fact that Intel never made it
> work and never shipped it.

OTOH it _is_ used in virtualization. KVM supports it and it just
works. That's how I found out that XEN explodes in colourful ways :)

Thanks,

        tglx