linux-kernel - [PATCH v2 02/38] x86/tsc: Add standalone helper for getting CPU frequency from CPUID

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Message-ID: <20250227021855.3257188-3-seanjc@google.com>
Date: Wed, 26 Feb 2025 18:18:18 -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>, Paolo Bonzini <pbonzini@...hat.com>, 
	Sean Christopherson <seanjc@...gle.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>, 
	Jan Kiszka <jan.kiszka@...mens.com>, Andy Lutomirski <luto@...nel.org>, 
	Peter Zijlstra <peterz@...radead.org>, Daniel Lezcano <daniel.lezcano@...aro.org>, 
	John Stultz <jstultz@...gle.com>
Cc: linux-kernel@...r.kernel.org, linux-coco@...ts.linux.dev, 
	kvm@...r.kernel.org, virtualization@...ts.linux.dev, 
	linux-hyperv@...r.kernel.org, xen-devel@...ts.xenproject.org, 
	Tom Lendacky <thomas.lendacky@....com>, Nikunj A Dadhania <nikunj@....com>
Subject: [PATCH v2 02/38] 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 |  1 +
 arch/x86/kernel/tsc.c      | 37 +++++++++++++++++++++++--------------
 2 files changed, 24 insertions(+), 14 deletions(-)

diff --git a/arch/x86/include/asm/tsc.h b/arch/x86/include/asm/tsc.h
index a4d84f721775..c3a14df46327 100644
--- a/arch/x86/include/asm/tsc.h
+++ b/arch/x86/include/asm/tsc.h
@@ -36,6 +36,7 @@ struct cpuid_tsc_info {
 };
 extern int cpuid_get_tsc_info(struct cpuid_tsc_info *info);
 extern int cpuid_get_tsc_freq(struct cpuid_tsc_info *info);
+extern int cpuid_get_cpu_freq(unsigned int *cpu_khz);
 
 extern void tsc_early_init(void);
 extern void tsc_init(void);
diff --git a/arch/x86/kernel/tsc.c b/arch/x86/kernel/tsc.c
index 93713eb81f52..bb4619148161 100644
--- a/arch/x86/kernel/tsc.c
+++ b/arch/x86/kernel/tsc.c
@@ -688,6 +688,24 @@ int cpuid_get_tsc_freq(struct cpuid_tsc_info *info)
 	return 0;
 }
 
+int cpuid_get_cpu_freq(unsigned int *cpu_khz)
+{
+	unsigned int eax_base_mhz, ebx, ecx, edx;
+
+	*cpu_khz = 0;
+
+	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;
+}
+
 /**
  * native_calibrate_tsc - determine TSC frequency
  * Determine TSC frequency via CPUID, else return 0.
@@ -723,13 +741,8 @@ 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 (!info.crystal_khz && 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);
-		info.crystal_khz = eax_base_mhz * 1000 *
-			info.denominator / info.numerator;
-	}
+	if (!info.crystal_khz && !cpuid_get_cpu_freq(&cpu_khz))
+		info.crystal_khz = cpu_khz * info.denominator / info.numerator;
 
 	if (!info.crystal_khz)
 		return 0;
@@ -756,19 +769,15 @@ 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;
 }
 
 /*
-- 
2.48.1.711.g2feabab25a-goog