linux-kernel - [PATCH 02/16] x86/tsc: Add standalone helper for getting CPU frequency from CPUID

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Message-ID: <20250201021718.699411-3-seanjc@google.com>
Date: Fri, 31 Jan 2025 18:17:04 -0800
From: Sean Christopherson <seanjc@...gle.com>
To: Thomas Gleixner <tglx@...utronix.de>, Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>, 
	Dave Hansen <dave.hansen@...ux.intel.com>, x86@...nel.org, 
	"Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>, Juergen Gross <jgross@...e.com>, 
	"K. Y. Srinivasan" <kys@...rosoft.com>, Haiyang Zhang <haiyangz@...rosoft.com>, Wei Liu <wei.liu@...nel.org>, 
	Dexuan Cui <decui@...rosoft.com>, Ajay Kaher <ajay.kaher@...adcom.com>, 
	Alexey Makhalov <alexey.amakhalov@...adcom.com>, Jan Kiszka <jan.kiszka@...mens.com>, 
	Paolo Bonzini <pbonzini@...hat.com>, Andy Lutomirski <luto@...nel.org>, 
	Peter Zijlstra <peterz@...radead.org>
Cc: linux-kernel@...r.kernel.org, linux-coco@...ts.linux.dev, 
	virtualization@...ts.linux.dev, linux-hyperv@...r.kernel.org, 
	jailhouse-dev@...glegroups.com, kvm@...r.kernel.org, 
	xen-devel@...ts.xenproject.org, Sean Christopherson <seanjc@...gle.com>, 
	Nikunj A Dadhania <nikunj@....com>, Tom Lendacky <thomas.lendacky@....com>
Subject: [PATCH 02/16] x86/tsc: Add standalone helper for getting CPU
 frequency from CPUID

Extract the guts of cpu_khz_from_cpuid() to a standalone helper that
doesn't restrict the usage to Intel CPUs.  This will allow sharing the
core logic with kvmclock, as (a) CPUID.0x16 may be enumerated alongside
kvmclock, and (b) KVM generally doesn't restrict CPUID based on vendor.

No functional change intended.

Signed-off-by: Sean Christopherson <seanjc@...gle.com>
---
 arch/x86/include/asm/tsc.h | 16 ++++++++++++++++
 arch/x86/kernel/tsc.c      | 21 ++++++---------------
 2 files changed, 22 insertions(+), 15 deletions(-)

diff --git a/arch/x86/include/asm/tsc.h b/arch/x86/include/asm/tsc.h
index 14a81a66b37c..540e2a31c87d 100644
--- a/arch/x86/include/asm/tsc.h
+++ b/arch/x86/include/asm/tsc.h
@@ -69,6 +69,22 @@ static inline int cpuid_get_tsc_freq(unsigned int *tsc_khz,
 	return 0;
 }
 
+static inline int cpuid_get_cpu_freq(unsigned int *cpu_khz)
+{
+	unsigned int eax_base_mhz, ebx, ecx, edx;
+
+	if (boot_cpu_data.cpuid_level < CPUID_LEAF_FREQ)
+		return -ENOENT;
+
+	cpuid(CPUID_LEAF_FREQ, &eax_base_mhz, &ebx, &ecx, &edx);
+
+	if (!eax_base_mhz)
+		return -ENOENT;
+
+	*cpu_khz = eax_base_mhz * 1000;
+	return 0;
+}
+
 extern void tsc_early_init(void);
 extern void tsc_init(void);
 extern void mark_tsc_unstable(char *reason);
diff --git a/arch/x86/kernel/tsc.c b/arch/x86/kernel/tsc.c
index e3faa2b36910..4fc633ac5873 100644
--- a/arch/x86/kernel/tsc.c
+++ b/arch/x86/kernel/tsc.c
@@ -662,7 +662,7 @@ static unsigned long quick_pit_calibrate(void)
 unsigned long native_calibrate_tsc(void)
 {
 	unsigned int eax_denominator, ebx_numerator;
-	unsigned int crystal_khz;
+	unsigned int crystal_khz, cpu_khz;
 
 	if (boot_cpu_data.x86_vendor != X86_VENDOR_INTEL)
 		return 0;
@@ -692,13 +692,8 @@ unsigned long native_calibrate_tsc(void)
 	 * clock, but we can easily calculate it to a high degree of accuracy
 	 * by considering the crystal ratio and the CPU speed.
 	 */
-	if (crystal_khz == 0 && boot_cpu_data.cpuid_level >= CPUID_LEAF_FREQ) {
-		unsigned int eax_base_mhz, ebx, ecx, edx;
-
-		cpuid(CPUID_LEAF_FREQ, &eax_base_mhz, &ebx, &ecx, &edx);
-		crystal_khz = eax_base_mhz * 1000 *
-			eax_denominator / ebx_numerator;
-	}
+	if (crystal_khz == 0 && !cpuid_get_cpu_freq(&cpu_khz))
+		crystal_khz = cpu_khz * eax_denominator / ebx_numerator;
 
 	if (crystal_khz == 0)
 		return 0;
@@ -725,19 +720,15 @@ unsigned long native_calibrate_tsc(void)
 
 static unsigned long cpu_khz_from_cpuid(void)
 {
-	unsigned int eax_base_mhz, ebx_max_mhz, ecx_bus_mhz, edx;
+	unsigned int cpu_khz;
 
 	if (boot_cpu_data.x86_vendor != X86_VENDOR_INTEL)
 		return 0;
 
-	if (boot_cpu_data.cpuid_level < CPUID_LEAF_FREQ)
+	if (cpuid_get_cpu_freq(&cpu_khz))
 		return 0;
 
-	eax_base_mhz = ebx_max_mhz = ecx_bus_mhz = edx = 0;
-
-	cpuid(CPUID_LEAF_FREQ, &eax_base_mhz, &ebx_max_mhz, &ecx_bus_mhz, &edx);
-
-	return eax_base_mhz * 1000;
+	return cpu_khz;
 }
 
 /*
-- 
2.48.1.362.g079036d154-goog