panic in page_private()

[jwk404]

This happened on a joyent_20130125T031721Z build using this kvm driver.
The AMD cpu I'm using is an old Athlon 64 4200+. The stack is always similar to this msgbuf excerpt:

[...the warning below repeats many times...]
WARNING: mmu_pages_clear_parents: unsync_children (-1)

WARNING: mmu_pages_clear_parents: unsync_children (-1)

WARNING: mmu_pages_clear_parents: unsync_children (-1)

panic[cpu1]/thread=ffffff02d8d793c0:
assertion failed: res != NULL, file: kvm_mmu.c, line: 3054

ffffff000f93ce60 fffffffffba66888 ()
ffffff000f93cfa0 kvm:page_private+77 ()
ffffff000f93cfd0 kvm:page_header+2e ()
ffffff000f93d030 kvm:__mmu_unsync_walk+ad ()
ffffff000f93d090 kvm:__mmu_unsync_walk+e4 ()
ffffff000f93d0f0 kvm:__mmu_unsync_walk+e4 ()
ffffff000f93d150 kvm:__mmu_unsync_walk+e4 ()
ffffff000f93d1a0 kvm:mmu_unsync_walk+55 ()
ffffff000f93d330 kvm:mmu_sync_children+151 ()
ffffff000f93d370 kvm:mmu_sync_roots+58 ()
ffffff000f93d3a0 kvm:kvm_mmu_load+56 ()
ffffff000f93d3c0 kvm:kvm_mmu_reload+20 ()
ffffff000f93d400 kvm:vcpu_enter_guest+66 ()
ffffff000f93d430 kvm:__vcpu_run+84 ()
ffffff000f93d480 kvm:kvm_arch_vcpu_ioctl_run+115 ()
ffffff000f93dcc0 kvm:kvm_ioctl+134 ()
ffffff000f93dd00 genunix:cdev_ioctl+39 ()
ffffff000f93dd50 specfs:spec_ioctl+60 ()
ffffff000f93dde0 genunix:fop_ioctl+55 ()
ffffff000f93df00 genunix:ioctl+9b ()
ffffff000f93df10 unix:brand_sys_syscall+1f5 ()

It'e easily reproducible, so I can provide crash dumps if needed.

[rmustacc]

@jclulow You'll be interested in this. We don't support AMD processes, so it wasn't from this repository. I think you're looking for http://github.com/jclulow/illumos-kvm