The guest_physmap_mark_populate_on_demand function in Xen 4.2 and earlier does not properly unlock the subject GFNs when checking if they are in use, which allows local guest HVM administrators to cause a denial of service (hang) via unspecified vectors.
Exploitability
AV:LAC:MAu:NImpact
C:NI:NA:C4.7/AV:L/AC:M/Au:N/C:N/I:N/A:C