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

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Message-ID: <175053192543.406.1923423835308666303.tip-bot2@tip-bot2>
Date: Sat, 21 Jun 2025 18:52:05 -0000
From: "tip-bot2 for Borislav Petkov (AMD)" <tip-bot2@...utronix.de>
To: linux-tip-commits@...r.kernel.org
Cc: "Borislav Petkov (AMD)" <bp@...en8.de>,
 Thomas Gleixner <tglx@...utronix.de>, x86@...nel.org,
 linux-kernel@...r.kernel.org
Subject: [tip: x86/cpu] x86/CPU/AMD: Add CPUID faulting support

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

Commit-ID:     65f55a30176662ee37fe18b47430ee30b57bfc98
Gitweb:        https://git.kernel.org/tip/65f55a30176662ee37fe18b47430ee30b57bfc98
Author:        Borislav Petkov (AMD) <bp@...en8.de>
AuthorDate:    Wed, 28 May 2025 23:31:05 +02:00
Committer:     Borislav Petkov (AMD) <bp@...en8.de>
CommitterDate: Sat, 21 Jun 2025 20:30:26 +02:00

x86/CPU/AMD: Add CPUID faulting support

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

Signed-off-by: Borislav Petkov (AMD) <bp@...en8.de>
Reviewed-by: Thomas Gleixner <tglx@...utronix.de>
Link: https://lore.kernel.org/20250528213105.1149-1-bp@kernel.org
---
 arch/x86/include/asm/cpufeatures.h |  3 +++
 arch/x86/include/asm/msr-index.h   |  1 +
 arch/x86/kernel/cpu/amd.c          |  4 ++++
 arch/x86/kernel/process.c          | 20 ++++++++++++++------
 4 files changed, 22 insertions(+), 6 deletions(-)

diff --git a/arch/x86/include/asm/cpufeatures.h b/arch/x86/include/asm/cpufeatures.h
index ee17623..b78af55 100644
--- a/arch/x86/include/asm/cpufeatures.h
+++ b/arch/x86/include/asm/cpufeatures.h
@@ -457,9 +457,12 @@
 #define X86_FEATURE_WRMSR_XX_BASE_NS	(20*32+ 1) /* WRMSR to {FS,GS,KERNEL_GS}_BASE is non-serializing */
 #define X86_FEATURE_LFENCE_RDTSC	(20*32+ 2) /* LFENCE always serializing / synchronizes RDTSC */
 #define X86_FEATURE_NULL_SEL_CLR_BASE	(20*32+ 6) /* Null Selector Clears Base */
+
 #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_PREFETCHI		(20*32+20) /* Prefetch Data/Instruction to Cache Level */
 #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 */
diff --git a/arch/x86/include/asm/msr-index.h b/arch/x86/include/asm/msr-index.h
index b7dded3..ff7e974 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 93da466..50f88fe 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 704883c..7b94851 100644
--- a/arch/x86/kernel/process.c
+++ b/arch/x86/kernel/process.c
@@ -334,13 +334,21 @@ 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)