page coalescing can dissociate locked pages from their pfn
Joyent encountered, and rectified, a particularly nasty (in practice) problem with the VM when KVM is used.
When coalescing pages, we treat locked pages as locked into memory, but not as locked at their specific physical location. Thus allowing the locked page to migrate out from under KVM and its mapping of guest to host memory. Not particularly predictable chaos then ensues.
We should pull Bryan's fix for this into illumos, to greatly ease the time of anyone using KVM.