Re: [Xen-devel] [RFC PATCH 71/84] x86/setup: start tearing down the direct map.

[<hongyax@xxxxxxxxxx>]

On 27/09/2019 14:00, Jan Beulich wrote:
> On 27.09.2019 14:54, hongyax@xxxxxxxxxx wrote:
>
> Pre-populate? There's some conceptional question then: When the
> direct map is gone, are you mapping Xen heap pages into the place
> they'd have lived at in the direct map? I'm not convinced that's
> what we want. In fact I'm not convinced we'd want to retain the
> distinction between Xen heap and domain heap then any further -
> there's no reason anymore at that point (afaict).
Yes. My patches map xenheap pages to where they would have lived on the direct 
map region, and unmap when xenheap pages are freed. The original proposal was 
to use vmap() which we find difficult to implement.
- vmap takes an array of mfns. Mapping a large region require 
allocating/freeing memory for a large array of mfns, unless we change or add 
another vmap variant.
- va<->pa conversion. Mapping xenheap to direct map region makes all the 
xenheap conversion macros still work. The vmap proposal needs to add another 
field in page_info (breaking the power of 2) or to have a separate structure 
somewhere else for va/pa conversion.
Of course, we could change all the code for xenheap to use the same domheap 
mapping structure, which is probably another large patch series.
Hongyan

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