attached is the vmx domain save/restore patch. works well for different 
guest/host combination W/O breaking domu save/restore according to my test.
pls. first apply xiaowei's qemu dm fix.

===know issue===
*  shpage pfn *
   HV look for shpage pfn in an e820 entry when init. but some 
guest(win/em64t linux) will reuse this e820 ram, which cause losing 
shpage pfn when restore. so this entry is marked as "reserved" to avoid 
guest reuse (in this patch xc_hvm_build.c).  we can change this if 
having good solution in future.

*  64bit host vmx restore python err *
    when restore vmx guest on em64t host, i got a error "ERROR 
(xmlrpclib2:167) int exceeds XML-RPC limits" W/O blocking restore. "xend 
restart" can be a work around.

*  guest smp support *
    i'm doing guest smp support including apic/vmcs save/restore now. so 
turn on "apic" in config file may cause save/restore failure.

*  guest save/restore across platform*
   e.g save 32 guest on 64 host, then restore 32 guest on 32 host.  we 
can't support this because save/restore face different vcpu_context 
format on different host. need universal format for this.

=== test report ===

"+" stands for okay, "-" stands for fail

    32b host:
        + 32/32
        + 32win/32

    pae host:
        + 32/pae
        + pae/pae
        + 32win/pae
        + pae_win/pae


    em64t host:
        + 32/64
        + pae/64
        + 64/64
        + 32win/64
        + pae_win/64

sometimes pae_win/64 are not stable:(