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

[Thomas Gleixner]

On Mon, 14 Nov 2016, Boris Ostrovsky wrote:
> On 11/13/2016 06:42 PM, M. Vefa Bicakci wrote:
> 
> > I found out that my domU kernels invoke the 'apic_disable' function
> > because CONFIG_X86_MPPARSE was not enabled in my kernel configuration,
> > which would cause the 'smp_found_config' bit to be unset at boot-up.
> 
> smp_found_config is not the problem, it is usually zero for Xen PV guests.
> 
> What is the problem is that because of your particular config selection
> acpi_mps_check() fails (with the error message that you mention below) and
> that leads to X86_FEATURE_APIC being cleared. And then we indeed switch to
> APIC noop and things go south after that.

Indeed. And what really puzzles me is that Xen manages to bring up a
secondary CPU despite APIC being disabled. 

There are quite some assumptions about no APIC == no SMP in all of x86. Can
we please make Xen behave like anything else?

Thanks,

	tglx