Racy interactions between dirty vram tracking and paging log dirty hypercalls

ISSUE DESCRIPTION Activation of log dirty mode done by XENDMOPtrackdirtyvram was named HVMOPtrackdirtyvram before Xen 4.9 is racy with ongoing log dirty hypercalls. A suitably timed call to XENDMOPtrackdirtyvram can enable log dirty while another CPU is still in the process of tearing down the...