> Would the above rely not only on TSC clocksource, but also > ka->use_master_clock==true? Yes this should only be in the case of master clock. Extra verification to check this for both GET/SET should be present. > What will happen if the vCPU=0 (e.g., BSP) thread is racing with here > to update the vcpu->arch.hv_clock? > In addition to live migration, can the user call this API any time > during the VM is running (to fix the clock drift)? Therefore, any > requirement to protect the update of kvmclock_offset from racing? This should occur when none of the vCPUs are running, in the context of a live-migration/update this would be after deserialization before the resume. I may have been unintentionally misleading here describing some of the problem space. There isn't a "drift" per say when a VM is running and the PVTI stays constant. It's more the relationship between the TSC & PV clock changes due to inaccuracy when KVM decides to generate that information, e.g on a live-update/migration KVM will perform the update. The KVM_REQ_MASTERCLOCK_UPDATE is just an example as to how to simulate/trigger this. I've posted a V2 which hopefully addresses some of above and makes it clearer overall the aim behind the patches.
