On systems that enumerate PPIN (protected processor inventory
number) using CPUID, but where the BIOS locked the MSR to
prevent access /proc/cpuinfo reports "intel_ppin" feature as
present on all logical CPUs except for CPU 0.

This happens because ppin_init() uses x86_match_cpu() to
determine whether PPIN is supported. When called on CPU 0
the test for locked PPIN MSR results in:

	clear_cpu_cap(c, info->feature);

This clears the X86 FEATURE bit in boot_cpu_data. When other
CPUs are brought online the x86_match_cpu() fails, and the
PPIN FEATURE bit remains set for those other CPUs.

Fix by using setup_clear_cpu_cap() instead of clear_cpu_cap()
which force clears the FEATURE bit for all CPUS.

Reported-by: Adeel Ashad <adeel.arshad@intel.com>
Signed-off-by: Tony Luck <tony.luck@intel.com>
---
 arch/x86/kernel/cpu/common.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/arch/x86/kernel/cpu/common.c b/arch/x86/kernel/cpu/common.c
index 02637365d1a9..52c3f941c2b1 100644
--- a/arch/x86/kernel/cpu/common.c
+++ b/arch/x86/kernel/cpu/common.c
@@ -169,7 +169,7 @@ static void ppin_init(struct cpuinfo_x86 *c)
 	}
 
 clear_ppin:
-	clear_cpu_cap(c, info->feature);
+	setup_clear_cpu_cap(info->feature);
 }
 
 static void default_init(struct cpuinfo_x86 *c)
-- 
2.47.0

The following commit has been merged into the x86/urgent branch of tip:

Commit-ID:     d9bb40544653cf039fe79225ec1d742183e2339a
Gitweb:        https://git.kernel.org/tip/d9bb40544653cf039fe79225ec1d742183e2339a
Author:        Tony Luck <tony.luck@intel.com>
AuthorDate:    Fri, 22 Nov 2024 15:42:12 -08:00
Committer:     Ingo Molnar <mingo@kernel.org>
CommitterDate: Mon, 25 Nov 2024 10:11:33 +01:00

x86/cpu: Fix PPIN initialization

On systems that enumerate PPIN (protected processor inventory
number) using CPUID, but where the BIOS locked the MSR to
prevent access /proc/cpuinfo reports "intel_ppin" feature as
present on all logical CPUs except for CPU 0.

This happens because ppin_init() uses x86_match_cpu() to
determine whether PPIN is supported. When called on CPU 0
the test for locked PPIN MSR results in:

	clear_cpu_cap(c, info->feature);

This clears the X86 FEATURE bit in boot_cpu_data. When other
CPUs are brought online the x86_match_cpu() fails, and the
PPIN FEATURE bit remains set for those other CPUs.

Fix by using setup_clear_cpu_cap() instead of clear_cpu_cap()
which force clears the FEATURE bit for all CPUS.

Reported-by: Adeel Ashad <adeel.arshad@intel.com>
Signed-off-by: Tony Luck <tony.luck@intel.com>
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Link: https://lore.kernel.org/r/20241122234212.27451-1-tony.luck@intel.com
---
 arch/x86/kernel/cpu/common.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/arch/x86/kernel/cpu/common.c b/arch/x86/kernel/cpu/common.c
index 06a516f..d9d2d19 100644
--- a/arch/x86/kernel/cpu/common.c
+++ b/arch/x86/kernel/cpu/common.c
@@ -169,7 +169,7 @@ static void ppin_init(struct cpuinfo_x86 *c)
 	}
 
 clear_ppin:
-	clear_cpu_cap(c, info->feature);
+	setup_clear_cpu_cap(info->feature);
 }
 
 static void default_init(struct cpuinfo_x86 *c)