Re: [PATCH v7 31/36] KVM: x86: Add KVM_[GS]ET_CLOCK_GUEST for accurate KVM clock migration
David Woodhouse <[email protected]>
| Newsgroups | gmane.comp.emulators.xen.devel,gmane.comp.emulators.kvm.devel,gmane.linux.documentation,gmane.linux.kernel |
|---|---|
| Message-ID | <[email protected]> |
On Fri, 2026-07-31 at 16:24 -0700, Sean Christopherson wrote:
>
> > + /*
> > + * Allow for a discrepancy of 1 kHz either way between the TSC
> > + * frequency used to generate the user's pvclock and the current
> > + * host's measured frequency, since they may not precisely match.
> > + */
> > + if (user_tsc_hz < curr_tsc_hz - 1000 ||
> > + user_tsc_hz > curr_tsc_hz + 1000) {
>
> I don't follow, why is KVM restricting what frequency userspace can set?
Userspace actually sets the frequency with KVM_SET_TSC_KHZ. What KVM is
insisting upon here is that the input to KVM_SET_CLOCK_GUEST is
*consistent* with the guest's TSC frequency (within a little slop
caused by different host TSCs).
I think the comment above it is fairly badly worded though ("host's
measured frequency"), so I'll fix that.
smime.p7s
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