From: Sean Christopherson <[email protected]> Sent: Wednesday, July 1, 2026 12:31 PM > > Add and use APIs to set the local APIC timer period instead of open coding > the subtle HZ math in a all external callers, and make lapic_timer_period
Spurious word "a". > local to apic.c. Provide APIs to specify the frequency in both hertz and > kilohertz so that Hyper-V and VMware code aren't forced to lose precision. > > Opportunistically use mul_u64_u32_div() to harden against the possibility > that the period in Khz is greater than 4294967, i.e. if the APIC timer runs > at ~4.29 GHz. As pointed out by Sashiko, 4294968 * 1000 == 0x1_000002c0, > and thus a Khz period of 4294968 would silently overflow the 32-bit > unsigned integer used by most callers. > > Signed-off-by: Sean Christopherson <[email protected]> > --- > arch/x86/include/asm/apic.h | 3 ++- > arch/x86/kernel/apic/apic.c | 12 +++++++++++- > arch/x86/kernel/cpu/mshyperv.c | 5 +---- > arch/x86/kernel/cpu/vmware.c | 4 +--- > arch/x86/kernel/jailhouse.c | 2 +- > arch/x86/kernel/tsc.c | 2 +- > arch/x86/kernel/tsc_msr.c | 2 +- > 7 files changed, 18 insertions(+), 12 deletions(-) > > diff --git a/arch/x86/include/asm/apic.h b/arch/x86/include/asm/apic.h > index 9cd493d467d4..cd84a94688a2 100644 > --- a/arch/x86/include/asm/apic.h > +++ b/arch/x86/include/asm/apic.h > @@ -63,7 +63,6 @@ extern int apic_verbosity; > extern int local_apic_timer_c2_ok; > > extern bool apic_is_disabled; > -extern unsigned int lapic_timer_period; > > extern enum apic_intr_mode_id apic_intr_mode; > enum apic_intr_mode_id { > @@ -138,6 +137,8 @@ void register_lapic_address(unsigned long address); > extern void setup_boot_APIC_clock(void); > extern void setup_secondary_APIC_clock(void); > extern void lapic_update_tsc_freq(void); > +extern void apic_set_timer_period_hz(u64 period_hz, const char *source); > +extern void apic_set_timer_period_khz(u64 period_khz, const char *source); > > #ifdef CONFIG_X86_64 > static inline bool apic_force_enable(unsigned long addr) > diff --git a/arch/x86/kernel/apic/apic.c b/arch/x86/kernel/apic/apic.c > index aa1e19979aa8..8d3d930576fd 100644 > --- a/arch/x86/kernel/apic/apic.c > +++ b/arch/x86/kernel/apic/apic.c > @@ -176,7 +176,7 @@ static struct resource lapic_resource = { > }; > > /* Measured in ticks per HZ. */ > -unsigned int lapic_timer_period = 0; > +static unsigned int lapic_timer_period; > > static void apic_pm_activate(void); > > @@ -796,6 +796,16 @@ bool __init apic_needs_pit(void) > return lapic_timer_period == 0; > } > > +void apic_set_timer_period_khz(u64 period_khz, const char *source) > +{ > + lapic_timer_period = mul_u64_u32_div(period_khz, 1000, HZ); > +} > + > +void apic_set_timer_period_hz(u64 period_hz, const char *source) > +{ > + lapic_timer_period = div_u64(period_hz, HZ); > +} A string "source" argument is passed in, but not used. Is there an envisioned future use? Also, this function doesn't output a pr_info() message like the existing Hyper-V and VMware code does. I don't know that the message is all that useful, though I do remember one case where I was debugging some clock/timer issue when I looked at it. Michael > + > static int __init calibrate_APIC_clock(void) > { > struct clock_event_device *levt = this_cpu_ptr(&lapic_events); > diff --git a/arch/x86/kernel/cpu/mshyperv.c b/arch/x86/kernel/cpu/mshyperv.c > index 185d4f677ec0..87beecec76f0 100644 > --- a/arch/x86/kernel/cpu/mshyperv.c > +++ b/arch/x86/kernel/cpu/mshyperv.c > @@ -646,10 +646,7 @@ static void __init ms_hyperv_init_platform(void) > u64 hv_lapic_frequency; > > rdmsrq(HV_X64_MSR_APIC_FREQUENCY, hv_lapic_frequency); > - hv_lapic_frequency = div_u64(hv_lapic_frequency, HZ); > - lapic_timer_period = hv_lapic_frequency; > - pr_info("Hyper-V: LAPIC Timer Frequency: %#x\n", > - lapic_timer_period); > + apic_set_timer_period_hz(hv_lapic_frequency, "Hyper-V > hypervisor"); > } > > register_nmi_handler(NMI_UNKNOWN, hv_nmi_unknown, NMI_FLAG_FIRST, > diff --git a/arch/x86/kernel/cpu/vmware.c b/arch/x86/kernel/cpu/vmware.c > index 34b73573b108..36f779dd311d 100644 > --- a/arch/x86/kernel/cpu/vmware.c > +++ b/arch/x86/kernel/cpu/vmware.c > @@ -424,9 +424,7 @@ static void __init vmware_platform_setup(void) > > #ifdef CONFIG_X86_LOCAL_APIC > /* Skip lapic calibration since we know the bus frequency. */ > - lapic_timer_period = ecx / HZ; > - pr_info("Host bus clock speed read from hypervisor : %u Hz\n", > - ecx); > + apic_set_timer_period_hz(ecx, "VMware hypervisor"); > #endif > } else { > pr_warn("Failed to get TSC freq from the hypervisor\n"); > diff --git a/arch/x86/kernel/jailhouse.c b/arch/x86/kernel/jailhouse.c > index f58ce9220e0f..f2d4ef89c085 100644 > --- a/arch/x86/kernel/jailhouse.c > +++ b/arch/x86/kernel/jailhouse.c > @@ -65,7 +65,7 @@ static void jailhouse_get_wallclock(struct timespec64 *now) > > static void __init jailhouse_timer_init(void) > { > - lapic_timer_period = setup_data.v1.apic_khz * (1000 / HZ); > + apic_set_timer_period_khz(setup_data.v1.apic_khz, "Jailhouse > hypervisor"); > } > > static unsigned long jailhouse_get_tsc(void) > diff --git a/arch/x86/kernel/tsc.c b/arch/x86/kernel/tsc.c > index ce10ae4b298b..f9ecc9256863 100644 > --- a/arch/x86/kernel/tsc.c > +++ b/arch/x86/kernel/tsc.c > @@ -717,7 +717,7 @@ unsigned long native_calibrate_tsc(void) > * lapic_timer_period here to avoid having to calibrate the APIC > * timer later. > */ > - lapic_timer_period = crystal_khz * 1000 / HZ; > + apic_set_timer_period_khz(crystal_khz, "CPUID 0x15/0x16"); > #endif > > return crystal_khz * ebx_numerator / eax_denominator; > diff --git a/arch/x86/kernel/tsc_msr.c b/arch/x86/kernel/tsc_msr.c > index 48e6cc1cb017..7e990871e041 100644 > --- a/arch/x86/kernel/tsc_msr.c > +++ b/arch/x86/kernel/tsc_msr.c > @@ -211,7 +211,7 @@ unsigned long cpu_khz_from_msr(void) > pr_err("Error MSR_FSB_FREQ index %d is unknown\n", index); > > #ifdef CONFIG_X86_LOCAL_APIC > - lapic_timer_period = (freq * 1000) / HZ; > + apic_set_timer_period_khz(freq, "MSR_FSB_FREQ"); > #endif > > /* > -- > 2.55.0.rc0.799.gd6f94ed593-goog >
