[PATCH V4 4/4] x86/topology: Fix duplicated core ID within a package

[Zhang Rui]

Today, core ID is assumed to be unique within each package.

But an AlderLake-N platform adds a Module level between core and package,
Linux excludes the unknown modules bits from the core ID, resulting in
duplicate core ID's.

To keep core ID unique within a package, Linux must include all APIC-ID
bits for known or un-known levels above the core and below the package
in the core ID.

It is important to understand that core ID's have always come directly
from the APIC-ID encoding, which comes from the BIOS. Thus there is no
guarantee that they start at 0, or that they are contiguous.
As such, naively using them for array indexes can be problematic.

Fixes: 7745f03eb395 ("x86/topology: Add CPUID.1F multi-die/package support")
Cc: stable@xxxxxxxxxxxxxxx
Suggested-by: Len Brown <len.brown@xxxxxxxxx>
Signed-off-by: Zhang Rui <rui.zhang@xxxxxxxxx>
Reviewed-by: Len Brown <len.brown@xxxxxxxxx>
---
 arch/x86/kernel/cpu/topology.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/arch/x86/kernel/cpu/topology.c b/arch/x86/kernel/cpu/topology.c
index f7592814e5d5..5e868b62a7c4 100644
--- a/arch/x86/kernel/cpu/topology.c
+++ b/arch/x86/kernel/cpu/topology.c
@@ -141,7 +141,7 @@ int detect_extended_topology(struct cpuinfo_x86 *c)
 		sub_index++;
 	}
 
-	core_select_mask = (~(-1 << core_plus_mask_width)) >> ht_mask_width;
+	core_select_mask = (~(-1 << pkg_mask_width)) >> ht_mask_width;
 	die_select_mask = (~(-1 << die_plus_mask_width)) >>
 				core_plus_mask_width;
 
-- 
2.25.1