Re: [PATCH v3 2/2] x86/acpi: Don't add CPUs that are not online capable

[Limonciello, Mario]

On 9/13/2021 12:23, Rafael J. Wysocki wrote:
> On Wed, Sep 8, 2021 at 11:41 PM Mario Limonciello
> <mario.limonciello@xxxxxxx> 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://nam11.safelinks.protection.outlook.com/?url=https%3A%2F%2Fuefi.org%2Fhtmlspecs%2FACPI_Spec_6_4_html%2F05_ACPI_Software_Programming_Model%2FACPI_Software_Programming_Model.html%3F%23local-apic-flags&amp;data=04%7C01%7Cmario.limonciello%40amd.com%7C081016240ab94e72822d08d976db3d0a%7C3dd8961fe4884e608e11a82d994e183d%7C0%7C0%7C637671506287828485%7CUnknown%7CTWFpbGZsb3d8eyJWIjoiMC4wLjAwMDAiLCJQIjoiV2luMzIiLCJBTiI6Ik1haWwiLCJXVCI6Mn0%3D%7C1000&amp;sdata=0vIs%2BDryYFVrtT1DvhU6Ke1BDJe%2BsIhbxPu94NeXRBo%3D&amp;reserved=0
> > Signed-off-by: Mario Limonciello <mario.limonciello@xxxxxxx>
>
> 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.

Sounds good, appreciate the diligence.

> 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