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

["Zhang, Rui" <rui.zhang@intel.com>]

On Thu, 2023-01-05 at 18:09 +0100, Rafael J. Wysocki wrote:
> On Thu, Jan 5, 2023 at 5:11 AM Kishon Vijay Abraham I <
> kvijayab@amd.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@alien8.de>
> > Reported-by: Leo Duran <leo.duran@amd.com>
> > Signed-off-by: Kishon Vijay Abraham I <kvijayab@amd.com>
> 
> Acked-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
> 

Reviewed-by: Zhang Rui <rui.zhang@intel.com>

thanks,
rui
> > ---
> > Changes from v1:
> > 1) Changed the ACPI spec version to 6.5 in the commit log
> > 2) Changed the Fixes tag to point to commit aa06e20f1be6
> > 3) Added "Reported-by: Leo Duran <leo.duran@amd.com>"
> >  arch/x86/kernel/acpi/boot.c | 19 ++++++++++++++++---
> >  1 file changed, 16 insertions(+), 3 deletions(-)
> > 
> > diff --git a/arch/x86/kernel/acpi/boot.c
> > b/arch/x86/kernel/acpi/boot.c
> > index 907cc98b1938..518bda50068c 100644
> > --- a/arch/x86/kernel/acpi/boot.c
> > +++ b/arch/x86/kernel/acpi/boot.c
> > @@ -188,6 +188,17 @@ static int acpi_register_lapic(int id, u32
> > acpiid, u8 enabled)
> >         return cpu;
> >  }
> > 
> > +static bool __init acpi_is_processor_usable(u32 lapic_flags)
> > +{
> > +       if (lapic_flags & ACPI_MADT_ENABLED)
> > +               return true;
> > +
> > +       if (acpi_support_online_capable && (lapic_flags &
> > ACPI_MADT_ONLINE_CAPABLE))
> > +               return true;
> > +
> > +       return false;
> > +}
> > +
> >  static int __init
> >  acpi_parse_x2apic(union acpi_subtable_headers *header, const
> > unsigned long end)
> >  {
> > @@ -212,6 +223,10 @@ acpi_parse_x2apic(union acpi_subtable_headers
> > *header, const unsigned long end)
> >         if (apic_id == 0xffffffff)
> >                 return 0;
> > 
> > +       /* don't register processors that cannot be onlined */
> > +       if (!acpi_is_processor_usable(processor->lapic_flags))
> > +               return 0;
> > +
> >         /*
> >          * We need to register disabled CPU as well to permit
> >          * counting disabled CPUs. This allows us to size
> > @@ -250,9 +265,7 @@ acpi_parse_lapic(union acpi_subtable_headers *
> > header, const unsigned long end)
> >                 return 0;
> > 
> >         /* don't register processors that can not be onlined */
> > -       if (acpi_support_online_capable &&
> > -           !(processor->lapic_flags & ACPI_MADT_ENABLED) &&
> > -           !(processor->lapic_flags & ACPI_MADT_ONLINE_CAPABLE))
> > +       if (!acpi_is_processor_usable(processor->lapic_flags))
> >                 return 0;
> > 
> >         /*
> > --
> > 2.34.1
> >