linux-kernel - [PATCH] x86/CPU/AMD: Add CPUID faulting support

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Message-ID: <20250528213105.1149-1-bp@kernel.org>
Date: Wed, 28 May 2025 23:31:05 +0200
From: Borislav Petkov <bp@...nel.org>
To: X86 ML <x86@...nel.org>
Cc: LKML <linux-kernel@...r.kernel.org>,
	"Borislav Petkov (AMD)" <bp@...en8.de>
Subject: [PATCH] x86/CPU/AMD: Add CPUID faulting support

From: "Borislav Petkov (AMD)" <bp@...en8.de>

Add CPUID faulting support on AMD using the same user interface.

Signed-off-by: Borislav Petkov (AMD) <bp@...en8.de>
---
 arch/x86/include/asm/cpufeatures.h |  2 ++
 arch/x86/include/asm/msr-index.h   |  1 +
 arch/x86/kernel/cpu/amd.c          |  4 ++++
 arch/x86/kernel/process.c          | 20 ++++++++++++++------
 4 files changed, 21 insertions(+), 6 deletions(-)

diff --git a/arch/x86/include/asm/cpufeatures.h b/arch/x86/include/asm/cpufeatures.h
index 5b50e0e35129..1e4fb02914a7 100644
--- a/arch/x86/include/asm/cpufeatures.h
+++ b/arch/x86/include/asm/cpufeatures.h
@@ -457,6 +457,8 @@
 #define X86_FEATURE_AUTOIBRS		(20*32+ 8) /* Automatic IBRS */
 #define X86_FEATURE_NO_SMM_CTL_MSR	(20*32+ 9) /* SMM_CTL MSR is not present */
 
+#define X86_FEATURE_GP_ON_USER_CPUID	(20*32+17) /* User CPUID faulting */
+
 #define X86_FEATURE_SBPB		(20*32+27) /* Selective Branch Prediction Barrier */
 #define X86_FEATURE_IBPB_BRTYPE		(20*32+28) /* MSR_PRED_CMD[IBPB] flushes all branch type predictions */
 #define X86_FEATURE_SRSO_NO		(20*32+29) /* CPU is not affected by SRSO */
diff --git a/arch/x86/include/asm/msr-index.h b/arch/x86/include/asm/msr-index.h
index b7dded3c8113..ff7e9743250f 100644
--- a/arch/x86/include/asm/msr-index.h
+++ b/arch/x86/include/asm/msr-index.h
@@ -830,6 +830,7 @@
 #define MSR_K7_HWCR_SMMLOCK		BIT_ULL(MSR_K7_HWCR_SMMLOCK_BIT)
 #define MSR_K7_HWCR_IRPERF_EN_BIT	30
 #define MSR_K7_HWCR_IRPERF_EN		BIT_ULL(MSR_K7_HWCR_IRPERF_EN_BIT)
+#define MSR_K7_HWCR_CPUID_USER_DIS_BIT	35
 #define MSR_K7_FID_VID_CTL		0xc0010041
 #define MSR_K7_FID_VID_STATUS		0xc0010042
 #define MSR_K7_HWCR_CPB_DIS_BIT		25
diff --git a/arch/x86/kernel/cpu/amd.c b/arch/x86/kernel/cpu/amd.c
index 93da466dfe2c..50f88fe51816 100644
--- a/arch/x86/kernel/cpu/amd.c
+++ b/arch/x86/kernel/cpu/amd.c
@@ -489,6 +489,10 @@ static void bsp_init_amd(struct cpuinfo_x86 *c)
 	}
 
 	bsp_determine_snp(c);
+
+	if (cpu_has(c, X86_FEATURE_GP_ON_USER_CPUID))
+		setup_force_cpu_cap(X86_FEATURE_CPUID_FAULT);
+
 	return;
 
 warn:
diff --git a/arch/x86/kernel/process.c b/arch/x86/kernel/process.c
index c1d2dac72b9c..3c104fb4753c 100644
--- a/arch/x86/kernel/process.c
+++ b/arch/x86/kernel/process.c
@@ -333,13 +333,21 @@ DEFINE_PER_CPU(u64, msr_misc_features_shadow);
 
 static void set_cpuid_faulting(bool on)
 {
-	u64 msrval;
 
-	msrval = this_cpu_read(msr_misc_features_shadow);
-	msrval &= ~MSR_MISC_FEATURES_ENABLES_CPUID_FAULT;
-	msrval |= (on << MSR_MISC_FEATURES_ENABLES_CPUID_FAULT_BIT);
-	this_cpu_write(msr_misc_features_shadow, msrval);
-	wrmsrq(MSR_MISC_FEATURES_ENABLES, msrval);
+	if (boot_cpu_data.x86_vendor == X86_VENDOR_INTEL) {
+		u64 msrval;
+
+		msrval = this_cpu_read(msr_misc_features_shadow);
+		msrval &= ~MSR_MISC_FEATURES_ENABLES_CPUID_FAULT;
+		msrval |= (on << MSR_MISC_FEATURES_ENABLES_CPUID_FAULT_BIT);
+		this_cpu_write(msr_misc_features_shadow, msrval);
+		wrmsrq(MSR_MISC_FEATURES_ENABLES, msrval);
+	} else if (boot_cpu_data.x86_vendor == X86_VENDOR_AMD) {
+		if (on)
+			msr_set_bit(MSR_K7_HWCR, MSR_K7_HWCR_CPUID_USER_DIS_BIT);
+		else
+			msr_clear_bit(MSR_K7_HWCR, MSR_K7_HWCR_CPUID_USER_DIS_BIT);
+	}
 }
 
 static void disable_cpuid(void)
-- 
2.43.0