Re: [tip:x86/apic] x86/acpi: Introduce persistent storage for cpuid <-> apicid mapping

From: Dou Liyang
Date: Fri Oct 07 2016 - 00:36:23 EST

Hi Yinghai

At 10/07/2016 05:20 AM, Yinghai Lu wrote:
On Thu, Oct 6, 2016 at 1:06 AM, Dou Liyang <douly.fnst@xxxxxxxxxxxxxx> wrote:

I seem to remember that in x2APIC Spec the x2APIC ID may be at 255 or

Good to know. Maybe later when one package have more cores like 30 cores etc.

If we do that judgment, it may be affect x2APIC's work in some other places.

I saw the MADT, the main reason may be that we define 0xff to acpi_id
in LAPIC mode.
As you said, it was like:
[ 42.107902] ACPI: LAPIC (acpi_id[0xff] lapic_id[0xff] disabled)
[ 42.120125] ACPI: LAPIC (acpi_id[0xff] lapic_id[0xff] disabled)
[ 42.132361] ACPI: LAPIC (acpi_id[0xff] lapic_id[0xff] disabled)

How about doing the acpi_id check when we parse it in


--- a/arch/x86/kernel/acpi/boot.c
+++ b/arch/x86/kernel/acpi/boot.c
@@ -233,6 +233,11 @@ acpi_parse_lapic(struct acpi_subtable_header * header,
const unsigned long end)


+ if (processor->id >= 255) {
+ ++disabled_cpus;
+ return -EINVAL;
+ }
* We need to register disabled CPU as well to permit
* counting disabled CPUs. This allows us to size

Yes, that should work. but should do the same thing for x2apic

in acpi_parse_x2apic should have

+ if (processor->local_apic_id == -1) {
+ ++disabled_cpus;
+ return -EINVAL;
+ }

that is the reason why i want to extend acpi_register_lapic()
to take extra disabled_id (one is 0xff and another is 0xffffffff)
so could save some lines.

Yes, I understood.
But I think adding an extra disabled_id is not a good way for
validating the apic_id. If the disabled_id is not just one id(-1 or
255), may be two or more, even be a range. what should we do for
extending our code?

Firstly, I am not sure that the "-1" could appear in the MADT, even if
the ACPI tables is unreasonable.

Seondly, I guess if we need the check, there are some reserved methods
in the kernel, such as "default_apic_id_valid", "x2apic_apic_id_valid"
and so on. we should extend all of them and use them for check.

CC'ed: Rafael and Lv

May I ask a question?

Is it possible that the "-1/oxffffffff" could appear in the MADT which is one of the ACPI tables?