On Tue, Mar 16, 2021 at 03:37:34PM +0100, Vitaly Kuznetsov wrote: > When KVM_REQ_MASTERCLOCK_UPDATE request is issued (e.g. after migration) > we need to make sure no vCPU sees stale values in PV clock structures and > thus all vCPUs are kicked with KVM_REQ_CLOCK_UPDATE. Hyper-V TSC page > clocksource is global and kvm_guest_time_update() only updates in on vCPU0 > but this is not entirely correct: nothing blocks some other vCPU from > entering the guest before we finish the update on CPU0 and it can read > stale values from the page. > > Invalidate TSC page in kvm_gen_update_masterclock() to switch all vCPUs > to using MSR based clocksource (HV_X64_MSR_TIME_REF_COUNT). Hi Vitaly, Not clear why this is necessary, if the choice was to not touch TSC page at all, when invariant TSC is supported on the host... Ah, OK, this is not for the migration with iTSC on destination case, but any call to kvm_gen_update_masterclock, correct?
