Re: [Xen-devel] [PATCH v3 0/3] xen/arm: fix "xen_add_mach_to_phys_entry: cannot add" problem

[Stefano Stabellini <stefano.stabellini@xxxxxxxxxxxxx>]

On Thu, 11 Sep 2014, David Vrabel wrote:
> On 11/09/14 00:28, Stefano Stabellini wrote:
> > On Fri, 1 Aug 2014, David Vrabel wrote:
> >> On 01/08/14 15:55, Stefano Stabellini wrote:
> >>> Hi all,
> >>> Xen support in Linux for ARM and ARM64 suffers from lack of support for
> >>> multiple mfn to pfn mappings: whenever a frontend grants the same page
> >>> multiple times to the backend, the mfn to pfn accounting in
> >>> arch/arm/xen/p2m.c fails. The issue has become critical since v3.15,
> >>> when xen-netfront/xen-netback switched from grant copies to grant
> >>> mappings, therefore causing the issue to happen much more often.
> >>>
> >>> Fixing the mfn to pfn accounting in p2m.c is difficult and expensive,
> >>> therefore we are looking for alternative solutions. One idea is avoiding
> >>> mfn to pfn conversions altogether. The only code path that needs them is
> >>> swiotlb-xen:unmap_page (and single_for_cpu and single_for_device).
> >>>
> >>> To avoid mfn to pfn conversions we rely on a second p2m mapping done by
> >>> Xen (a separate patch series will be sent for Xen). In Linux we use it
> >>> to perform the cache maintenance operations without mfns conversions.
> >>>
> >>>
> >>> The Xen side patch series that introduces XENFEAT_grant_map_identity is:
> >>> http://marc.info/?l=xen-devel&m=140690433923855
> >>
> >> If the Xen side is in master, you can apply this series to
> >> devel/for-linus-3.17
> > 
> > The Xen side patch finally went in. Unfortunately it's probably too late
> > for 3.17.
> 
> Isn't this a bug fix?  I think would be fine to go into 3.17.
 
Yes, you are right, it is a bug fix. I was being too conservative.

I applied it to stable/for-linus-3.17-b

Do you have any more fixes queued up to send to Linus for 3.17?

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