Re: [Qemu-devel] [PATCH v1] kvm/x86: Hyper-V tsc page setup

[Andrey Smetanin]

On 01/22/2016 02:53 PM, Paolo Bonzini wrote:
> On 22/01/2016 12:31, Andrey Smetanin wrote:
> > > Sometimes the TSC is detected to be unstable and Linux switches to
> > > another clocksource.  At least in that case you can get a write to the
> > > TSC page while the guest is running.
> > Sorry, now I got it, you mean host TSC is unstable and we should mark
> > guest tsc page invalid. Now I understand please ignore my prev. message.
>
> No problem.  Anyhow yes, this is what I meant: a host write to the TSC
> page, not a guest write to the TSC page MSR.
>
> Usually it happens only at migration time to update the sequence---which
> I believe your patch wasn't doing either.
QEMU saves address of page inside ->msr_hv_tsc, so at restore
QEMU sets corresponding MSR and KVM setup's tsc page again.
So migration should able to work.
 But if we tie TSC page
> updates to kvm_gen_update_masterclock, we get that for free when the
> migration destination calls the KVM_SET_CLOCK ioctl.
>
> Paolo