On Mon, Mar 27, 2023 at 03:10:26PM -0400, Eric DeVolder wrote:
> The logic in acpi_is_processor_usable() requires the Online Capable
> bit be set for hotpluggable cpus. The Online Capable bit is
> introduced in ACPI 6.3 and MADT.revision 5.
I can't find where in the spec it says that MADT.revision 5 means that
bit is present?
I'm looking at:
aa06e20f1be6 ("x86/ACPI: Don't add CPUs that are not online capable")
Mario?
I see in the 6.3 spec it says:
"1948 Adds a “Hot-plug Capable” flag to the Local APIC and x2APIC structures in MADT"
and the MADT.revision is 5 and in the 6.2 spec the MADT revision is "45"
- 4.5 maybe?
But I don't see the connection between MADT.revision 5 and the presence
of the online capable bit.
Anyone got a better quote?
> However, as currently coded, for MADT.revision < 5,
> acpi_is_processor_usable() no longer allows for possible hot
> pluggable cpus, which is a regressive change in behavior.
>
> This patch restores the behavior where for MADT.revision < 5, the
Avoid having "This patch" or "This commit" in the commit message. It is
tautologically useless.
Also, do
$ git grep 'This patch' Documentation/process
for more details.
> presence of the lapic/x2apic structure implies a possible hotpluggable
> cpu.
>
> Fixes: e2869bd7af60 ("x86/acpi/boot: Do not register processors that cannot be onlined for x2APIC")
> Suggested-by: Miguel Luis <miguel.luis@xxxxxxxxxx>
> Suggested-by: Boris Ostrovsky <boris.ovstrosky@xxxxxxxxxx>
> Signed-off-by: Eric DeVolder <eric.devolder@xxxxxxxxxx>
> ---
> arch/x86/kernel/acpi/boot.c | 8 +++++++-
> 1 file changed, 7 insertions(+), 1 deletion(-)
>
> diff --git a/arch/x86/kernel/acpi/boot.c b/arch/x86/kernel/acpi/boot.c
> index 1c38174b5f01..7b5b8ed018b0 100644
> --- a/arch/x86/kernel/acpi/boot.c
> +++ b/arch/x86/kernel/acpi/boot.c
> @@ -193,7 +193,13 @@ 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))
> + /*
> + * Prior to MADT.revision 5, the presence of the Local x2/APIC
> + * structure _implicitly_ noted a possible hotpluggable cpu.
> + * Starting with MADT.revision 5, the Online Capable bit
> + * _explicitly_ indicates a hotpluggable cpu.
> + */
In all your text
s/cpu/CPU/g
> + if (!acpi_support_online_capable || (lapic_flags & ACPI_MADT_ONLINE_CAPABLE))
> return true;
>
> return false;
> --
Otherwise, the change makes sense to me.
Thx.
--
Regards/Gruss,
Boris.
https://people.kernel.org/tglx/notes-about-netiquette
