On Thu, May 21, 2026, David Woodhouse wrote:
> On Thu, 2026-05-21 at 13:53 -0700, Sean Christopherson wrote:
> >
> > E.g. this is what I've got for the early flow. Testing now.
> >
> > void __init tsc_early_init(void)
> > {
> > unsigned int known_cpu_khz = 0, known_tsc_khz = 0;
> >
> > if (!boot_cpu_has(X86_FEATURE_TSC))
> > return;
> > /* Don't change UV TSC multi-chassis synchronization */
> > if (is_early_uv_system())
> > return;
> >
> > if (x86_init.hyper.get_cpu_khz)
> > known_cpu_khz = x86_init.hyper.get_cpu_khz();
> >
> > if (tsc_early_khz)
> > known_tsc_khz = tsc_early_khz;
> > else if (cc_platform_has(CC_ATTR_GUEST_SNP_SECURE_TSC))
> > known_tsc_khz = snp_secure_tsc_init();
> > else if (boot_cpu_has(X86_FEATURE_TDX_GUEST))
> > known_tsc_khz = tdx_tsc_init();
> >
> > /*
> > * If the TSC frequency is still unknown, i.e. not provided by the user
> > * or by trusted firmware, try to get it from the hypervisor (which is
> > * untrusted when running as a CoCo guest).
> > */
> > if (!known_tsc_khz && x86_init.hyper.get_tsc_khz)
> > known_tsc_khz = x86_init.hyper.get_tsc_khz();
> >
> > if (known_tsc_khz)
> > setup_force_cpu_cap(X86_FEATURE_TSC_KNOWN_FREQ);
> >
> > if (!determine_cpu_tsc_frequencies(true, known_cpu_khz, known_tsc_khz))
> > return;
> > tsc_enable_sched_clock();
> > }
>
> That seems reasonable. Where does the call to native_calibrate_tsc()
> happen; is that from determine_cpu_tsc_frequencies()?
Yep.
static bool __init determine_cpu_tsc_frequencies(bool early,
unsigned int known_cpu_khz,
unsigned int known_tsc_khz)
{
/* Make sure that cpu and tsc are not already calibrated */
WARN_ON(cpu_khz || tsc_khz);
if (early) {
/*
* Early CPU calibration can only use methods that are available
* early in boot (obviously).
*/
if (known_cpu_khz)
cpu_khz = known_cpu_khz;
else
cpu_khz = native_calibrate_cpu_early();
if (known_tsc_khz)
tsc_khz = known_tsc_khz;
else
tsc_khz = native_calibrate_tsc();
} else {
cpu_khz = pit_hpet_ptimer_calibrate_cpu();
}
...
