linux-kernel - Re: [PATCH] x86/ACPI/boot: Use FADT version to check support for online capable

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Date:   Thu, 30 Mar 2023 20:23:38 +0200
From:   "Rafael J. Wysocki" <rafael@...nel.org>
To:     Mario Limonciello <mario.limonciello@....com>, x86@...nel.org
Cc:     "Rafael J. Wysocki" <rafael@...nel.org>,
        Len Brown <len.brown@...el.com>, Pavel Machek <pavel@....cz>,
        Eric DeVolder <eric.devolder@...cle.com>,
        Borislav Petkob <bp@...en8.de>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>,
        Dave Hansen <dave.hansen@...ux.intel.com>,
        "H. Peter Anvin" <hpa@...or.com>, linux-pm@...r.kernel.org,
        linux-kernel@...r.kernel.org,
        ACPI Devel Maling List <linux-acpi@...r.kernel.org>
Subject: Re: [PATCH] x86/ACPI/boot: Use FADT version to check support for
 online capable

On Wed, Mar 29, 2023 at 7:46 PM Mario Limonciello
<mario.limonciello@....com> wrote:
>
> ACPI 6.3 introduced the online capable bit, and also introduced MADT
> version 5.
>
> This was used to distinguish whether the offset storing online capable
> could be used. However ACPI 6.2b has MADT version "45" which is for
> an errata version of the ACPI 6.2 spec.  This means that the Linux code
> for detecting availability of MADT will mistakingly flag ACPI 6.2b as
> supporting online capable which is inaccurate as it's an ACPI 6.3 feature.
>
> Instead use the FADT major and minor revision fields to distingush this.
>
> Reported-by: Eric DeVolder <eric.devolder@...cle.com>
> Reported-by: Borislav Petkob <bp@...en8.de>

s/Petkob/Petkov/ I suppose?

Would have been nice to CC this to linux-acpi (done now).

Anyway, x86 guys, are you going to handle this or do you want me to do that?

> Fixes: aa06e20f1be6 ("x86/ACPI: Don't add CPUs that are not online capable")
> Signed-off-by: Mario Limonciello <mario.limonciello@....com>
> ---
>  arch/x86/kernel/acpi/boot.c | 5 ++++-
>  1 file changed, 4 insertions(+), 1 deletion(-)
>
> diff --git a/arch/x86/kernel/acpi/boot.c b/arch/x86/kernel/acpi/boot.c
> index 1c38174b5f01..e92e3292fef7 100644
> --- a/arch/x86/kernel/acpi/boot.c
> +++ b/arch/x86/kernel/acpi/boot.c
> @@ -146,7 +146,10 @@ static int __init acpi_parse_madt(struct acpi_table_header *table)
>
>                 pr_debug("Local APIC address 0x%08x\n", madt->address);
>         }
> -       if (madt->header.revision >= 5)
> +
> +       if (acpi_gbl_FADT.header.revision > 6 ||
> +           (acpi_gbl_FADT.header.revision == 6 &&
> +            acpi_gbl_FADT.minor_revision >= 3))
>                 acpi_support_online_capable = true;
>
>         default_acpi_madt_oem_check(madt->header.oem_id,
> --
> 2.34.1
>