linux-kernel - Re: [PATCH v2] x86/acpi/boot: Do not register processors that cannot be onlined for x2apic

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Message-ID: <CAJZ5v0iq1_kSOXuBcteXrCJR0NyyBVXcio_L=47oKrACT1oaZQ@mail.gmail.com>
Date:   Tue, 10 Jan 2023 14:03:48 +0100
From:   "Rafael J. Wysocki" <rafael@...nel.org>
To:     Borislav Petkov <bp@...en8.de>
Cc:     "Rafael J. Wysocki" <rafael@...nel.org>,
        Kishon Vijay Abraham I <kvijayab@....com>,
        Len Brown <len.brown@...el.com>, Pavel Machek <pavel@....cz>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>,
        Dave Hansen <dave.hansen@...ux.intel.com>, x86@...nel.org,
        "H. Peter Anvin" <hpa@...or.com>, linux-pm@...r.kernel.org,
        linux-kernel@...r.kernel.org,
        Santosh Shukla <santosh.shukla@....com>,
        Suravee Suthikulpanit <suravee.suthikulpanit@....com>,
        Borislav Petkov <bpetkov@....com>,
        Leo Duran <leo.duran@....com>
Subject: Re: [PATCH v2] x86/acpi/boot: Do not register processors that cannot
 be onlined for x2apic

On Thu, Jan 5, 2023 at 11:22 PM Borislav Petkov <bp@...en8.de> wrote:
>
> On Thu, Jan 05, 2023 at 06:09:59PM +0100, Rafael J. Wysocki wrote:
> > On Thu, Jan 5, 2023 at 5:11 AM Kishon Vijay Abraham I <kvijayab@....com> wrote:
> > >
> > > Section 5.2.12.12 Processor Local x2APIC Structure in the ACPI v6.5
> > > spec mandates that both "enabled" and "online capable" Local APIC Flags
> > > should be used to determine if the processor is usable or not.
> > >
> > > However, Linux doesn't use the "online capable" flag for x2APIC to
> > > determine if the processor is usable. As a result, cpu_possible_mask has
> > > incorrect value and results in more memory getting allocated for per_cpu
> > > variables than it is going to be used.
> > >
> > > Make sure Linux parses both "enabled" and "online capable" flags for
> > > x2APIC to correctly determine if the processor is usable.
> > >
> > > Fixes: aa06e20f1be6 ("x86/ACPI: Don't add CPUs that are not online capable")
> > > Reviewed-by: Borislav Petkov (AMD) <bp@...en8.de>
> > > Reported-by: Leo Duran <leo.duran@....com>
> > > Signed-off-by: Kishon Vijay Abraham I <kvijayab@....com>
> >
> > Acked-by: Rafael J. Wysocki <rafael.j.wysocki@...el.com>
>
> Are you saying, I should take it through tip?

Works for me either way.

Just please let me know if I need to take care of it. :-)