Re: Rebooting domu fails in nfs share exported from another domu on the same dom0

[annie li <annie.li@oracle.com>]

On 2014/7/17 11:49, Roger Pau Monné wrote:
> On 16/07/14 22:36, annie li wrote:
>> Hi
>>
>> I hit a problem in such scenario: vm1 is running and export nfs service,
>> dom0 mount this nfs, and vm2 is booted in this nfs location. vm1 and vm2
>> are running on the same dom0.
>>
>> When this bug happens, the data flow is:  vm2 blkfront-> vm2 blkback->
>> loop -> nfs file -> nfs client -> bridge priv1 -> vm1 vif -> vm1 netback
>> -> vm1 netfront.
>>
>> In above data flow, nfs implements direct io, blkfront and blkback uses
>> grantmap. This makes page mapping works well through vm2 blkfront to vm1
>> netback. However, when netback does grant copy, the error happens in
>> this routine:
> If it's the same error I was seeing (which I think it is), the problem
> is due to trying to do a grant_copy with the PFN of a grant mapped page
> in Dom0, which Xen refuses to perform.
>
> I've never followed it up, but I think the problem should be fixed in
> Linux, so that netback realises it is trying to perform a grant_copy to
> a granted page, and use the grant ref instead of the PFN.
>

I guess the routine is similar if using grant ref. See __gnttab_copy 
function,
The routine goes into __acquire_grant_for_copy for grant ref, and then 
__get_paged_frame->get_page_from_gfn->get_page.  get_page is where the 
checking page owner fails.

Thanks
Annie