Messages in this thread | | | Date | Mon, 27 Mar 2023 15:07:23 -0500 | Subject | Re: [PATCH 1/1] x86/acpi: acpi_is_processor_usable() dropping possible cpus | From | Eric DeVolder <> |
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On 3/27/23 14:57, Borislav Petkov wrote: > 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?
Boris,
https://ueif.org/sites/default/files/resources/ACPI_6_3_May16.pdf Section 5.2.12 MADT. Table 5-43 is the MADT Revision is numbered 5. However, ACPI 6.x specs got a little "sloppy" with Revision, as this is what I uncovered:
ACPI MADT Changes 6.0 3 Section 5.2.12 6.0a 4 Section 5.2.12 Adds ARM GIC structure types 0xB-0xF 6.2a 45 Section 5.2.12 <--- yep it says version 45! 6.2b 5 Section 5.2.12 GIC ITS last Reserved offset changed to 16 from 20 (typo) 6.3 5 Section 5.2.12 Adds Local APIC Flags Online Capable! Adds GICC SPE Overflow Interrupt field 6.4 5 Section 5.2.12 Adds Multiprocessor Wakeup Structure type 0x10 6.5 5 Section 5.2.12
At any rate, Section 5.2.12.2 Processor Local APIC structure, has Table 5-47 which is the Local APIC Structure Flags, and this is where Online Capable is introduced for the first time.
> >> 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. ok!
> > Also, do > > $ git grep 'This patch' Documentation/process > > for more details. ok, will do!
> >> 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@oracle.com> >> Suggested-by: Boris Ostrovsky <boris.ovstrosky@oracle.com> >> Signed-off-by: Eric DeVolder <eric.devolder@oracle.com> >> --- >> 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 ok, will do! > >> + if (!acpi_support_online_capable || (lapic_flags & ACPI_MADT_ONLINE_CAPABLE)) >> return true; >> >> return false; >> -- > > Otherwise, the change makes sense to me. ok!
> > Thx. >
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