Description of problem:
On an ia64 dom0, attempting to run:

# xm save <hvm-guest> /var/lib/xen/save/hvm-guest-save

on an HVM guest fails to do anything.  In particular, it writes out the header
file to /var/lib/xen/save/hvm-guest-save, but doesn't write any data in there. 
It also doesn't pause the domain.  Note that there seem to be no ill effects on
either the guest or the dom0; the save just doesn't work.  In
/var/log/xen/xend.log, I see the following:

[2007-08-24 14:52:15 xend 2663] DEBUG (XendCheckpoint:88) [xc_save]:
/usr/lib/xen/bin/xc_save 20 4 0 0 4[2007-08-24 14:52:15 xend 2663] INFO
(XendCheckpoint:338) ERROR Internal error: Couldn't map live_shinfo
[2007-08-24 14:52:15 xend 2663] INFO (XendCheckpoint:338) Save exit rc=1
[2007-08-24 14:52:15 xend 2663] ERROR (XendCheckpoint:132) Save failed on domain
r5hvm (4).
Traceback (most recent call last):
  File "/usr/lib/python2.4/site-packages/xen/xend/XendCheckpoint.py", line 109,
in save
    forkHelper(cmd, fd, saveInputHandler, False)
  File "/usr/lib/python2.4/site-packages/xen/xend/XendCheckpoint.py", line 326,
in forkHelper
    raise XendError("%s failed" % string.join(cmd))
XendError: /usr/lib/xen/bin/xc_save 20 4 0 0 4 failed
[2007-08-24 14:52:15 xend.XendDomainInfo 2663] DEBUG (XendDomainInfo:1598)
XendDomainInfo.resumeDomain(4)
[2007-08-24 14:52:15 xend.XendDomainInfo 2663] ERROR (XendDomainInfo:1628)
XendDomainInfo.resume: xc.domain_resume failed on domain 4.
Traceback (most recent call last):
  File "/usr/lib/python2.4/site-packages/xen/xend/XendDomainInfo.py", line 1625,
in resumeDomain
    xc.domain_resume(self.domid, fast)
Error: (38, 'Function not implemented')
[2007-08-24 14:52:15 xend 2663] DEBUG (XendCheckpoint:135) XendCheckpoint.save:
resumeDomain