linux-kernel - Re: [PATCH] x86/cpuid: Deal with broken firmware once more

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Date:   Thu, 10 Nov 2016 18:13:40 +0100 (CET)
From:   Thomas Gleixner <tglx@...utronix.de>
To:     Boris Ostrovsky <boris.ostrovsky@...cle.com>
cc:     "M. Vefa Bicakci" <m.v.b@...box.com>,
        Sebastian Andrzej Siewior <bigeasy@...utronix.de>,
        "Charles (Chas) Williams" <ciwillia@...cade.com>,
        "x86@...nel.org" <x86@...nel.org>,
        LKML <linux-kernel@...r.kernel.org>,
        Peter Zijlstra <peterz@...radead.org>,
        Borislav Petkov <bp@...en8.de>,
        David Vrabel <david.vrabel@...rix.com>,
        Juergen Gross <jgross@...e.com>,
        xen-devel <xen-devel@...ts.xen.org>
Subject: Re: [PATCH] x86/cpuid: Deal with broken firmware once more

On Thu, 10 Nov 2016, Boris Ostrovsky wrote:
> On 11/10/2016 10:12 AM, Thomas Gleixner wrote:
> > On Thu, 10 Nov 2016, Boris Ostrovsky wrote:
> >> By firmware you mean ACPI? It is most likely not available to PV guests.
> > You either have to provide ACPI or MP tables. And either of those has to
> > provide the intial APIC ids for the CPUs. They are supposed to match the
> > IDs which are in the CPUID leafs.
> >
> >> How about returning cpu_data(cpu).initial_apicid?
> > For a not yet brought up CPU. That's what the initial ACPI/MP table
> > enumeration is for.
> 
> Unfortunately PV guests have neither. So we may need to emulate
> something in xen_cpu_present_to_apicid().

SFI does the same thing and according to the dmesg which was posted, this
is using SFI. We also have devicetree based boot concept which provides the
APICids in the CPU enumeration at boot time in a way which the whole x86
machinery is expecting.

So what kind of APICid is XEN handing in via SFI? None, or just an invalid
one?

Thanks,

	tglx