linux-kernel - [tip: x86/cpu] x86/cpu/topology: Define AMD64_CPUID_EXT

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Message-ID: <175810126585.709179.4725030483865525356.tip-bot2@tip-bot2>
Date: Wed, 17 Sep 2025 09:27:45 -0000
From: "tip-bot2 for K Prateek Nayak" <tip-bot2@...utronix.de>
To: linux-tip-commits@...r.kernel.org
Cc: K Prateek Nayak <kprateek.nayak@....com>,
 "Borislav Petkov (AMD)" <bp@...en8.de>, Ingo Molnar <mingo@...nel.org>,
 x86@...nel.org, linux-kernel@...r.kernel.org
Subject: [tip: x86/cpu] x86/cpu/topology: Define AMD64_CPUID_EXT_FEAT MSR

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

Commit-ID:     bc6397cf0bc4f2b7a47cc6ac44086daf67c3c71c
Gitweb:        https://git.kernel.org/tip/bc6397cf0bc4f2b7a47cc6ac44086daf67c3c71c
Author:        K Prateek Nayak <kprateek.nayak@....com>
AuthorDate:    Mon, 01 Sep 2025 17:04:17 
Committer:     Ingo Molnar <mingo@...nel.org>
CommitterDate: Wed, 17 Sep 2025 11:24:33 +02:00

x86/cpu/topology: Define AMD64_CPUID_EXT_FEAT MSR

Add defines for the 0xc001_1005 MSR (Core::X86::Msr::CPUID_ExtFeatures) used
to toggle the extended CPUID features, instead of using literal numbers. Also
define and use the bits necessary for an old TOPOEXT fixup on AMD Family 0x15
processors.

No functional changes intended.

  [ bp: Massage, rename MSR to adhere to the documentation name. ]

Signed-off-by: K Prateek Nayak <kprateek.nayak@....com>
Signed-off-by: Borislav Petkov (AMD) <bp@...en8.de>
Signed-off-by: Ingo Molnar <mingo@...nel.org>
Link: https://lore.kernel.org/20250901170418.4314-1-kprateek.nayak@amd.com
---
 arch/x86/include/asm/msr-index.h   | 5 +++++
 arch/x86/kernel/cpu/topology_amd.c | 7 ++++---
 2 files changed, 9 insertions(+), 3 deletions(-)

diff --git a/arch/x86/include/asm/msr-index.h b/arch/x86/include/asm/msr-index.h
index b65c3ba..a734b56 100644
--- a/arch/x86/include/asm/msr-index.h
+++ b/arch/x86/include/asm/msr-index.h
@@ -631,6 +631,11 @@
 #define MSR_AMD_PPIN			0xc00102f1
 #define MSR_AMD64_CPUID_FN_7		0xc0011002
 #define MSR_AMD64_CPUID_FN_1		0xc0011004
+
+#define MSR_AMD64_CPUID_EXT_FEAT	0xc0011005
+#define MSR_AMD64_CPUID_EXT_FEAT_TOPOEXT_BIT	54
+#define MSR_AMD64_CPUID_EXT_FEAT_TOPOEXT	BIT_ULL(MSR_AMD64_CPUID_EXT_FEAT_TOPOEXT_BIT)
+
 #define MSR_AMD64_LS_CFG		0xc0011020
 #define MSR_AMD64_DC_CFG		0xc0011022
 #define MSR_AMD64_TW_CFG		0xc0011023
diff --git a/arch/x86/kernel/cpu/topology_amd.c b/arch/x86/kernel/cpu/topology_amd.c
index 7ebd4a1..6ac097e 100644
--- a/arch/x86/kernel/cpu/topology_amd.c
+++ b/arch/x86/kernel/cpu/topology_amd.c
@@ -163,11 +163,12 @@ static void topoext_fixup(struct topo_scan *tscan)
 	    c->x86 != 0x15 || c->x86_model < 0x10 || c->x86_model > 0x6f)
 		return;
 
-	if (msr_set_bit(0xc0011005, 54) <= 0)
+	if (msr_set_bit(MSR_AMD64_CPUID_EXT_FEAT,
+			MSR_AMD64_CPUID_EXT_FEAT_TOPOEXT_BIT) <= 0)
 		return;
 
-	rdmsrq(0xc0011005, msrval);
-	if (msrval & BIT_64(54)) {
+	rdmsrq(MSR_AMD64_CPUID_EXT_FEAT, msrval);
+	if (msrval & MSR_AMD64_CPUID_EXT_FEAT_TOPOEXT) {
 		set_cpu_cap(c, X86_FEATURE_TOPOEXT);
 		pr_info_once(FW_INFO "CPU: Re-enabling disabled Topology Extensions Support.\n");
 	}