Using disk image from NFS crashes kernel

[Roger Pau Monné <roger.pau%entel.upc.edu@localhost>]

Hello,

I'm trying to use shared Xen disk images, over a NFS server. But when
starting a guest that has the hard drive on an NFS share I get the
following kernel crash:

balloon0 at xenbus0 id 0: Xen Balloon driver
balloon0: current reservation: 524288 KiB
balloon0: current reservation: 131072 pages => target: 131072 pages
xbd backend: attach device vnd0d (size 10240000) for domain 2
mapping kernel into physical memory
about to get started...
panic: kernel diagnostic assertion "pg != NULL" failed: file
"/usr/src/sys/uvm/uvm_pager.c", line 489
cpu0: Begin traceback...
copyright() at ffffffff8097ceed
uvm_pageratop() at netbsd:uvm_pageratop+0x7e
nfs_doio() at netbsd:nfs_doio+0x1f9
nfssvc_iod() at netbsd:nfssvc_iod+0x17b
cpu0: End traceback...

My kernel version is 5.99.52, and I'm running xen-unstable (although I
think this bug is not related to xen itself).

Regards, Roger.