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SubjectRe: [PATCH] Move APIC ID validity check into platform APIC code
On 3/14/2012 18:58, Yinghai Lu wrote:
> On Wed, Mar 14, 2012 at 12:17 AM, Daniel J Blueman
[]
>
> can you check if you can update
>
> !cpu_has_x2apic&& (apic_id>= 0xff)&& enabled
>
> in arch/x86/kernel/acpi/boot.c::acpi_parse_x2apic()
>
> to use some kind of apic_id_valid()
>
> so you could avoid setting that feature bit.
>
> the checking in SRAT could be removed.
>

Yinghai/Team,

One question (as I don't really know *why* this was added to the
acpi/srat parsing code). In arch/x86/kernel/smpboot.c the check was
originally :

!x2apic_mode && apicid >= 255

However in arch/x86/kernel/acpi/boot.c and arch/x86/mm/srat.c these
tests are used :

!cpu_has_x2apic && (apic_id >= 0xff)

Clearly, "cpu_has_x2apic" and "x2apic_mode" are two different things.

Since we can force "cpu_has_x2apic", when Daniel crafted this patch he
made the following "default" function :

static inline int default_apic_id_valid(int apicid)
{
return x2apic_mode || (apicid < 255);
}
which, as you can see, checks against "x2apic_mode".

My question is; Is checking for "x2apic_mode" going to do the trick in
the arch/x86/kernel/acpi/boot.c::acpi_parse_x2apic() ?

If the answer is yes, the patch is going to be very simple. But we can't
verify that the code in arch/x86/kernel/acpi/boot.c::acpi_parse_x2apic()
actually triggers for the case you wanted it to trigger for because then
it will check against "x2apic_mode" and not "cpu_has_x2apic".

Cheers,
--
Steffen Persvold, Chief Architect NumaChip
Numascale AS - www.numascale.com
Tel: +47 92 49 25 54 Skype: spersvold


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