Re: [kvm-devel] [PATCH 2/3] kvmclock - the host part.

[Dong, E. <edd...@in...>]

>>=20
>> +	kvm_get_msr(vcpu, MSR_IA32_TIME_STAMP_COUNTER,
>> +			  &vcpu->hv_clock.last_tsc);
>> +
>> +	ktime_get_ts(&ts);
>> +	vcpu->hv_clock.now_ns =3D ts.tv_nsec + (NSEC_PER_SEC *
>> (u64)ts.tv_sec); +	vcpu->hv_clock.wc_sec =3D get_seconds();
>>=20
>> I am even thinking we have to disable interrupt between these lines,
>> otherwise guest wall clock may see backward time source when
>> calculating the delta TSC since last vcpu->hv_clock.now_ns update.
>>=20
>=20
> That's true.  While we do need to handle vcpu migration and
> descheduling, the code sequence you note needs to be as atomic as
> possible.=20
>=20

Yes VCPU migration is another issue. Since the physical platform TSC is=20
totally different across migration, so we can't expose host TSC to
guest.
For KVM, it should be simple to just use guest_TSC (=3DHOST_TSC + =
offset).

thanks, eddie