Re: [Xen-ia64-devel] [Patch] Fix for re-enabling PV-on-HVM on IPF

[Doi.Tsunehisa@xxxxxxxxxxxxxx]

You (yamahata) said:
>>   Currently, without this patch, hypervisor crashes in PV-on-HVM
>> initialization phase..
>> 
>>   * at share_info page remapping: success
>>     - called from HYPERVISOR_memory_op in init_xen_info()..
>>       (unmodified_drivers/linux-2.6/platform-pci/platform-pci.c)
>>   * at grant table page remapping: crash
>>     - called from gnttab_init() in init_xen_info()
>>     - call tree in driver code is 
>>       gnttab_init() -> gnttab_resume() -> gnttab_map()
>>          -> HYPERVISOR_memory_op
>>       (linux-2.6-xen-sparse/drivers/xen/core/gnttab.c)
>>     - at guest_physmap_add_page() in hypervisor code,
>
> 
> The grant table shared pages are owned by the domain
> so that get_page() shouldn't fail.
> 
> Why get_page() fails?
> The c/s 14010:01476c7804b2 of xen-ia64-unstable.hg twists
> the grant table initialization a little.
> Does it affect on vt-i domain initialization?

  I've checked the reason of get_page() failing, so the domain
owner is correct, but the reference counter becomes zero at the
crash point.. 

  And, I've tracked the counter, so it be cleared below:

[xen/arch/ia64/xen/mm.c]
....
long
arch_memory_op(int op, XEN_GUEST_HANDLE(void) arg)
{
....
        /* Unmap from old location, if any. */
        gpfn = get_gpfn_from_mfn(mfn);
        if (gpfn != INVALID_M2P_ENTRY)
            guest_physmap_remove_page(d, gpfn, mfn);
....


  I'll investigate it more.

Thanks,
- Tsunehisa Doi


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