Re: [Xen-devel] [[PATCH for-4.13]] xen/arm: mm: Allow generic xen page-tables helpers to be called early

[Julien Grall <julien.grall@xxxxxxx>]

Hi Hongyan,

On 11/10/2019 10:53, Xia, Hongyan wrote:
> Not commenting on the patch, but I had exactly the same problem when
> removing the direct map in x86. map_domain_page has to be usable
> without the direct map and even before alloc_boot_pages can be used (so
> that I can map the bootmem_regions_list, although I have made it
> statically allocated now).
>
> The direct map teardown series in the end introduces a persistent
> mapping infrastructure to map page tables which occupies a few fixmap
> entries, and avoid set_fixmap but instead modify the entries directly
> to avoid invocation loops. The result is that map_xen_pagetable and
> map_domain_page is usable from the very beginning of start_xen.
Would you mind to point to the patch adding the implementation on x86?

On arm32, we are not using a direct map. So we are using a per-cpu mapping (see 
map_domain_page() implementation in arch/arm/mm.c).
On arm64, we are using the direct map so far. But we could use any of the two 
solutions if needed.
Cheers,

--
Julien Grall

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