[Xen-ia64-devel] Patch for PV-on-HVM for IPF

[DOI Tsunehisa <Doi.Tsunehisa@xxxxxxxxxxxxxx>]

Hi all,

  Currently, we are testing PV-on-HVM driver for IPF. so, we found
a problem that hypervisor crashes during VT-i domain destruction
with PV-on-HVM driver.

  The procedure to reproduce this problem are:

   * Create a VT-i domain.
     [dom0]# xm create -f hvm.conf
   * Insert modules for PV-on-HVM on the domain.
     [domvti]# insmod xen-platform-pci.ko
     [domvti]# insmod xenbus.ko
     [domvti]# insmod xen-vbd.ko
     [domvti]# insmod xen-vnif.ko
   * Activate VNIF network interface.
     [dom0]# xm network-attach <domid> eth1
     [domvti]# ifconfig eth1 up
   * Destruct the domain
     [dom0]# xm destroy <domid>
     ..... hypervisor crash  ....

  We were investigating the hypervisor crash mechanism, thus we found
a reason of it.

  * VNIF of PV-on-HVM uses gnttab_copy() function.
    - it's used for copy-method of VNIF backend.
    - it needs to refer p2m table.
  * gnttab_copy() function may be called during the domain destruction.
    - it's called by dom0 VNIF backend.
  * Hypervisor invalidates p2m table at first during the destruction.
    - gnttab_copy() won't be able to refer p2m table, thus it occurs
      hypervisor crash.
    - In x86 code, p2m table invalidation is delayed at last phase of
      domain destruction.
      => but we don't like it. it seems that p2m table exists after
         memory relinquised.

  So, I'll post a patch to avoid hypervisor crash.

   * pv-avoid-crash.patch
     + modify p2m table converter (gmfn_to_mfn_foreign())
       - return INVALID_MFN during VT-i domain destruction

  We tested that the problem is solved.

Thanks,
- Tsunehisa Doi


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