Re: [PATCH v3 40/41] x86/tsc: Add standalone helper for getting CPU frequency from CPUID

[Sean Christopherson <seanjc@google.com>]

On Fri, May 15, 2026, sashiko-bot@kernel.org wrote:
> Thank you for your contribution! Sashiko AI review found 1 potential issue(s) to consider:
> - [High] Unintended clobbering of the global `cpu_khz` variable in `native_calibrate_tsc()` due to a missing local variable declaration.
> --
> 
> commit 36e45379d4c9f40ae24c5c323b4f0471c94c6bef
> Author: Sean Christopherson <seanjc@google.com>
> 
> x86/tsc: Add standalone helper for getting CPU frequency from CPUID
> 
> This commit extracts the logic for getting the CPU frequency via CPUID into
> a new standalone helper function. It also updates the TSC calibration code
> to use this new helper.
> 
> > diff --git a/arch/x86/kernel/tsc.c b/arch/x86/kernel/tsc.c
> > --- a/arch/x86/kernel/tsc.c
> > +++ b/arch/x86/kernel/tsc.c
> 
> [ ... ]
> 
> > @@ -754,13 +772,8 @@ 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;
> 
> Does this unintentionally clobber the global cpu_khz variable?

Yep.  I don't think I even realized there was such a global variable.  Probably
makes sense to use a different name for the local variables.