[PATCH v5 23/51] x86/tsc: Add standalone helper for getting CPU frequency from CPUID
From: Sean Christopherson <seanjc@google.com>
Date: 2026-07-01 19:32:55
Also in:
kvm, linux-coco, linux-hyperv, lkml, virtualization, xen-devel
Subsystem:
the rest, x86 architecture (32-bit and 64-bit) · Maintainers:
Linus Torvalds, Thomas Gleixner, Ingo Molnar, Borislav Petkov, Dave Hansen
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 KVM-as-a-guest, as KVM generally doesn't restrict CPUID based on vendor. No functional change intended. Reviewed-by: David Woodhouse <redacted> Signed-off-by: Sean Christopherson <seanjc@google.com> --- arch/x86/include/asm/tsc.h | 1 + arch/x86/kernel/tsc.c | 31 +++++++++++++++---------------- 2 files changed, 16 insertions(+), 16 deletions(-)
diff --git a/arch/x86/include/asm/tsc.h b/arch/x86/include/asm/tsc.h
index c09ec485abcd..cb682f097ea7 100644
--- a/arch/x86/include/asm/tsc.h
+++ b/arch/x86/include/asm/tsc.h@@ -88,6 +88,7 @@ struct cpuid_tsc_info { unsigned int crystal_khz; }; extern int cpuid_get_tsc_info(struct cpuid_tsc_info *info); +extern unsigned int __cpu_khz_from_cpuid(void); 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 6ed6f8f012eb..56e73e96920a 100644
--- a/arch/x86/kernel/tsc.c
+++ b/arch/x86/kernel/tsc.c@@ -668,6 +668,18 @@ int cpuid_get_tsc_info(struct cpuid_tsc_info *info) return 0; } +unsigned int __cpu_khz_from_cpuid(void) +{ + unsigned int eax_base_mhz, ebx, ecx, edx; + + if (boot_cpu_data.cpuid_level < CPUID_LEAF_FREQ) + return 0; + + cpuid(CPUID_LEAF_FREQ, &eax_base_mhz, &ebx, &ecx, &edx); + + return eax_base_mhz * 1000; +} + /** * native_calibrate_tsc - determine TSC frequency * Determine TSC frequency via CPUID, else return 0.
@@ -703,12 +715,8 @@ static 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) + info.crystal_khz = __cpu_khz_from_cpuid() * info.denominator / info.numerator; if (!info.crystal_khz) return 0;
@@ -733,19 +741,10 @@ static 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; - if (boot_cpu_data.x86_vendor != X86_VENDOR_INTEL) return 0; - if (boot_cpu_data.cpuid_level < CPUID_LEAF_FREQ) - 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_from_cpuid(); } /*
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2.55.0.rc0.799.gd6f94ed593-goog