Re: [PATCH] x86: fix boot time APIC mode detection

[Andrew Cooper <andrew.cooper3@citrix.com>]

On 23/05/13 08:07, Jan Beulich wrote:
> current_cpu_data becomes valid only relatively late in the boot
> process, so looking there for a particular feature early in the game
> would generally give the appearance of the feature being unavailable.
>
> Getting this wrong means that at kexec time the system would get
> returned to xAPIC mode, causing disconnect_bsp_APIC() to try to access
> the APIC page, which on systems with x2APIC pre-enabled will never get
> set up.
>
> Signed-off-by: Jan Beulich <jbeulich@suse.com>

Reviewed-by: Andrew Cooper <andrew.cooper3@citrix.com>

>
> --- a/xen/arch/x86/apic.c
> +++ b/xen/arch/x86/apic.c
> @@ -1474,7 +1474,7 @@ enum apic_mode current_local_apic_mode(v
>  
>      /* Reading EXTD bit from the MSR is only valid if CPUID
>       * says so, else reserved */
> -    if ( cpu_has(&current_cpu_data, X86_FEATURE_X2APIC)
> +    if ( boot_cpu_has(X86_FEATURE_X2APIC)
>           && (msr_contents & MSR_IA32_APICBASE_EXTD) )
>          return APIC_MODE_X2APIC;
>  
>
>
>