Re: [Xen-devel] [PATCH RFC v2 1/4] x86/mm: Shadow and p2m changes for PV mem_access

["Jan Beulich" <JBeulich@xxxxxxxx>]

>>> On 04.09.14 at 10:39, <tim@xxxxxxx> wrote:
>> Tim, can you think of any other options here?
> 
> It might be possible to make the walk restartable if we arrange that:
> - all additions to the page list are at the tail;
> - walks in progress are recorded (though I'm not sure where: it might
>   be possible just to use a single bit in the page_info to say "this
>   page is the cursor of an interrupted walk" and have a separate
>   per-domain list of interrupted walks); and
> - anything that removes a page from a domain's page_list must check
>   that bit; if it finds it set it must update the per-walk state to
>   point to the next page.
> 
> Jan, do you think that's viable?  I think it'll need a bit of thought
> around the edge cases, and the semantics will need to be written down
> carefully.

Yes, nice idea - I think that could work (with particularly converting
arch_iommu_populate_page_table() to use that mechanism, while
inspecting [and perhaps adjusting] the related code in
p2m_pod_offline_or_broken_hit()) and would not end up being too
ugly (i.e. not exactly nice, but maintainable).

Jan


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