Messages in this thread | | | Subject | Re: Re: [PATCH v2 1/2] x86/cpu: Introduce x86_get_cpufreq_khz() | From | zhenwei pi <> | Date | Fri, 3 Dec 2021 15:34:04 +0800 |
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On 12/3/21 6:25 AM, Peter Zijlstra wrote: > On Wed, Dec 01, 2021 at 10:46:49AM +0800, zhenwei pi wrote: >> Wrapper function x86_get_cpufreq_khz() to get frequency on a x86 >> platform, hide detailed implementation from proc routine. >> >> Also export this function for the further use, a typical case is that >> kvm module gets the frequency of the host and tell the guest side by >> kvmclock. > > This function was already complete crap, and now you want to export it, > *WHY* ?! > > What possible use does KVM have for this random number generator? > A KVM guest overwrites the '.calibrate_tsc' and '.calibrate_cpu' if kvmclock is supported:
in function kvmclock_init(void) (linux/arch/x86/kernel/kvmclock.c) ... x86_platform.calibrate_tsc = kvm_get_tsc_khz; x86_platform.calibrate_cpu = kvm_get_tsc_khz; ...
And kvm_get_tsc_khz reads PV data from host side. Before guest reads this, KVM should writes the frequency into the PV data structure.
And the problem is that KVM gets tsc_khz directly without aperf/mperf detection. So user may gets different frequency(cat /proc/cpuinfo) from guest & host.
Or is that possible to export function 'aperfmperf_get_khz'?
-- zhenwei pi
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