Re: [Xen-devel] Rebooting domu fails in nfs share exported from another domu on the same dom0

[Konrad Rzeszutek Wilk <konrad.wilk@xxxxxxxxxx>]

On Thu, Jul 17, 2014 at 12:56:12PM -0400, annie li wrote:
> 
> 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->

I am a bit confused here. 'vm2 blkfront -> vm2 blkback'? Did you
mean 'dom0 blkback'?


> >>loop -> nfs file -> nfs client -> bridge priv1 -> vm1 vif -> vm1 netback
> >>-> vm1 netfront.

So both netback and netfront run in the same guest? I think you
want these two swapped around (netfront -> netback).

> >>
> >>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
> 
> 
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