Hi,

gntdev doesn't even try to handle forking.  I wouldn't be surprised if
that is a great way to kill Domain-0.  The xen hypervisor will most
likely not be amused to find a pte refering to a granted (but foreign)
page which wasn't established using the grant table interface.  Pinning
the pgd of the child process will most likely fail and make the kernel
BUG().

Ok, isn't that bad thanks to the VM_DONTCOPY.  The child just doesn't
get the grant mapping.

cheers,
  Gerd