Re: [PATCH][2.5-AC] Forced enable/disable local APIC

[Maciej W. Rozycki]

On Thu, 7 Nov 2002, Mikael Pettersson wrote:

> Zwane Mwaikambo writes:
>  > +int enable_local_apic_flag __initdata = 0; /* 0=probe, 1=force, 2=disable e.g. DMI */
> ...
>  > +	if (enable_local_apic_flag == 1)
>  > +		goto force_apic;
>  >  
>  >  	switch (boot_cpu_data.x86_vendor) {
>  >  	case X86_VENDOR_AMD:
>  > @@ -642,6 +661,7 @@
>  >  		goto no_apic;
>  >  	}
>  >  
>  > +force_apic:
>  >  	if (!cpu_has_apic) {
>  >  		/*
>  >  		 * Some BIOSes disable the local APIC in the
> 
> Of what use is the force case? If someone boots with "lapic" on a CPU
> where the APIC feature bit is off, then the code will rdmsr/wrmsr on
> APICBASE, even though we (the kernel) haven't verified that the CPU
> actually has that MSR. This is doubleplusungood.

 The assumption is a user knows better what he wants to achieve.  But I'm
not sure we really need it here.  A DMI override with the APICBASE
availability test in place should suffice -- I'd remove the "goto". 

-- 
+  Maciej W. Rozycki, Technical University of Gdansk, Poland   +
+--------------------------------------------------------------+
+        e-mail: [e-mail], PGP key available        +