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