Change in coreboot[master]: cpu/x86/lapic: Support switching to X2APIC mode

[Kyösti Mälkki (Code Review)]

Attention is currently required from: Angel Pons.
Kyösti Mälkki has posted comments on this change. ( https://review.coreboot.org/c/coreboot/+/55262 )

Change subject: cpu/x86/lapic: Support switching to X2APIC mode
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Patch Set 10:

(2 comments)

Patchset:

PS8:
> Looks like it's some serialization issue. […]

Where do you need is_x2apic_mode() to return false? There might be a problem with initial_lapicid() and lapicid() being stashed.

This makes X2APIC_ONLY work?

diff --git a/src/include/cpu/x86/lapic.h b/src/include/cpu/x86/lapic.h
    index 4fbae88ca5..50417acca5 100644
    --- a/src/include/cpu/x86/lapic.h
    +++ b/src/include/cpu/x86/lapic.h
    @@ -75,11 +75,12 @@ static inline bool is_x2apic_mode(void)
    	if (CONFIG(XAPIC_ONLY))
    		return false;
     
    +       msr_t msr;
    +       msr = rdmsr(LAPIC_BASE_MSR);
    +
    	if (CONFIG(X2APIC_ONLY))
    		return true;
     
    -       msr_t msr;
    -       msr = rdmsr(LAPIC_BASE_MSR);
    	return ((msr.lo & LAPIC_BASE_X2APIC_ENABLED) == LAPIC_BASE_X2APIC_ENABLED);
     }

File src/cpu/x86/lapic/lapic.c:

https://review.coreboot.org/c/coreboot/+/55262/comment/8ba352a4_3077e4fc 
PS10, Line 37: 		ASSERT(CONFIG(X2APIC_RUNTIME) | use_x2apic);
Should have been a logical OR here.