Re: [Xen-devel] [Xen-users] ARM: "xen_add_mach_to_phys_entry: cannot add ... already exists and panics"

[Stefano Stabellini <stefano.stabellini@xxxxxxxxxxxxx>]

On Fri, 4 Jul 2014, David Vrabel wrote:
> On 03/07/14 18:47, Stefano Stabellini wrote:
> > 
> > At the moment I would like a way to disable grant mappings and go back
> > to grant copies on demand. Maybe we could have a feature flag to change
> > the behaviour of the network backend?
> 
> You must fix the ARM code to handle this properly.
> 
> blkback also uses grant maps and depending on the frontend blkback may
> grant map the same machine frame multiple time.  We have see frontends
> that send such requests.

Indeed, it must be fixed properly. The workaround of disabling grant
mappings would be just to buy us some time to come up with the fix.


> I can't remember how the ARM code works.  Where is the problematic m2p
> lookup?

arch/arm/xen/p2m.c


> Perhaps this could be avoided for foreign frames?

Unfortunately no. The whole point of p2m.c is to be able to translate
foreign frames for dma operations.

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