[Xen-devel] Re: Changeset 20209 causes an issue in xen_in_range()

["Jan Beulich" <JBeulich@xxxxxxxxxx>]

>>> "Cui, Dexuan" <dexuan.cui@xxxxxxxxx> 14.01.10 09:38 >>>
>We may have 2 options:
>1) enhance xen_in_range() and check the freed pages. This means we should 
>refer to the logic of percpu_free_unused_areas().
>2) don't free the unused per_cpu pages: we will waste NR_CPUS pages. e.g., if 
>NR_CPUS is 256, we'll waste 1M memory. Looks this is not a big issue?
>
>I personally perfer option 2 as it's simple :-)

I would definitely prefer option 1. Even more I would prefer a solution to 
avoid allocating two pages of per-CPU data when only one is needed, though 
doing that would seem tricky.

>And actually long ago we also had frame_table checked in xen_in_range(), but  
>gave up the checking later as it's not easy to implement the exact checking.

That's certainly not the only set of ranges of concern. We either trust Dom0 or 
need a general mechanism (perhaps using range sets) to track all memory in use 
by Xen. Under tboot, the former may not be an option...

Jan


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