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

["Aravindh Puthiyaparambil (aravindp)" <aravindp@xxxxxxxxx>]

>> 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).

As I was looking into implementing this, I notice that the functions won't be 
called for PV domains. So I assume this implementation is a generic mechanism 
to make page_list walks pre-emptible and not specific to the PV mem_access use 
case. If that is the case I would prefer committing this as a separate patch in 
the 4.6 time frame and follow it up with the PV mem_access patch. Is that 
agreeable?

Thanks,
Aravindh


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