Messages in this thread | | | From | "Rafael J. Wysocki" <> | Date | Mon, 13 Sep 2021 19:23:32 +0200 | Subject | Re: [PATCH v3 2/2] x86/acpi: Don't add CPUs that are not online capable |
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On Wed, Sep 8, 2021 at 11:41 PM Mario Limonciello <mario.limonciello@amd.com> wrote: > > A number of systems are showing "hotplug capable" CPUs when they > are not really hotpluggable. This is because the MADT has extra > CPU entries to support different CPUs that may be inserted into > the socket with different numbers of cores. > > Starting with ACPI 6.3 the spec has an Online Capable bit in the > MADT used to determine whether or not a CPU is hotplug capable > when the enabled bit is not set. > > Link: https://uefi.org/htmlspecs/ACPI_Spec_6_4_html/05_ACPI_Software_Programming_Model/ACPI_Software_Programming_Model.html?#local-apic-flags > Signed-off-by: Mario Limonciello <mario.limonciello@amd.com>
I've added the patches in this series to my queue, but given what this one does, I think that it's a bit risky, because it exposes the kernel to a new category of possible platform firmware bugs.
For this reason, I'd rather queue it up as 5.16 material (and of course x86 reviewer comments are welcome).
> --- > arch/x86/kernel/acpi/boot.c | 9 +++++++++ > 1 file changed, 9 insertions(+) > > Changes from v1 -> v2: > * Make the change only apply on ACPI 6.3 or later > Changes from v2 -> v3: > * Make acpi_support_online_capable static and only valid if CONFIG_X86_LOCAL_APIC is defined > diff --git a/arch/x86/kernel/acpi/boot.c b/arch/x86/kernel/acpi/boot.c > index e55e0c1fad8c..d915f01b582b 100644 > --- a/arch/x86/kernel/acpi/boot.c > +++ b/arch/x86/kernel/acpi/boot.c > @@ -62,6 +62,7 @@ int acpi_fix_pin2_polarity __initdata; > > #ifdef CONFIG_X86_LOCAL_APIC > static u64 acpi_lapic_addr __initdata = APIC_DEFAULT_PHYS_BASE; > +static bool acpi_support_online_capable; > #endif > > #ifdef CONFIG_X86_IO_APIC > @@ -138,6 +139,8 @@ 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) > + acpi_support_online_capable = true; > > default_acpi_madt_oem_check(madt->header.oem_id, > madt->header.oem_table_id); > @@ -239,6 +242,12 @@ acpi_parse_lapic(union acpi_subtable_headers * header, const unsigned long end) > if (processor->id == 0xff) > 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)) > + return 0; > + > /* > * We need to register disabled CPU as well to permit > * counting disabled CPUs. This allows us to size > -- > 2.25.1 >
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