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

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Date:   Thu, 6 Oct 2016 14:20:24 -0700
From:   Yinghai Lu <yinghai@...nel.org>
To:     Dou Liyang <douly.fnst@...fujitsu.com>
Cc:     Thomas Gleixner <tglx@...utronix.de>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Ingo Molnar <mingo@...nel.org>,
        "H. Peter Anvin" <hpa@...or.com>,
        "linux-tip-commits@...r.kernel.org" 
        <linux-tip-commits@...r.kernel.org>,
        Tony Luck <tony.luck@...el.com>
Subject: Re: [tip:x86/apic] x86/acpi: Introduce persistent storage for cpuid
 <-> apicid mapping

On Thu, Oct 6, 2016 at 1:06 AM, Dou Liyang <douly.fnst@...fujitsu.com> wrote:

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

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
> acpi_parse_lapic().
>
> 8<----------------
>
> --- 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)
>
>         acpi_table_print_madt_entry(header);
>
> +       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.

Thanks

Yinghai