linux-kernel - [PATCH] x86/cpu: Fix PPIN initialization

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Message-ID: <20241122234212.27451-1-tony.luck@intel.com>
Date: Fri, 22 Nov 2024 15:42:12 -0800
From: Tony Luck <tony.luck@...el.com>
To: x86@...nel.org
Cc: linux-kernel@...r.kernel.org,
	patches@...ts.linux.dev,
	Tony Luck <tony.luck@...el.com>,
	Adeel Ashad <adeel.arshad@...el.com>
Subject: [PATCH] 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@...el.com>
Signed-off-by: Tony Luck <tony.luck@...el.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