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@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
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.
