Messages in this thread | | | From | Vishal Annapurve <> | Date | Fri, 6 Oct 2023 08:27:19 -0700 | Subject | Re: [PATCH] x86/tdx: Override the tsc calibration for TDX VMs |
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On Fri, Oct 6, 2023 at 7:03 AM Dave Hansen <dave.hansen@intel.com> wrote: > > On 10/5/23 18:12, Vishal Annapurve wrote: > > +/** > > + * Determine TSC frequency via CPUID, else return 0. > > + */ > > +static unsigned long tdx_calibrate_tsc(void) > > +{ > > + unsigned int eax_denominator = 0, ebx_numerator = 0, ecx_hz = 0, edx = 0; > > + unsigned int crystal_khz; > > + > > + /* CPUID 15H TSC/Crystal ratio, plus optionally Crystal Hz */ > > + cpuid(0x15, &eax_denominator, &ebx_numerator, &ecx_hz, &edx); > > + > > + if (ebx_numerator == 0 || eax_denominator == 0) > > + return 0; > > + > > + crystal_khz = ecx_hz / 1000; > > + > > + /* > > + * TSC frequency reported directly by CPUID is a "hardware reported" > > + * frequency and is the most accurate one so far we have. This > > + * is considered a known frequency. > > + */ > > + if (crystal_khz != 0) > > + setup_force_cpu_cap(X86_FEATURE_TSC_KNOWN_FREQ); > > + > > + return crystal_khz * ebx_numerator / eax_denominator; > > +} > > + > > Would it be possible to do this by refactoring the existing code and > calling it directly instead of copying and pasting so much?
One option is to call native_calibrate_tsc from tdx_calibrate_tsc and undo the lapic_timer_period configuration after the call. Does that sound reasonable?
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