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xen-devel
[Xen-devel] Re: HYBRID: gnttab_map() to map shared frames..
On Tue, 18 Oct 2011 09:13:02 +0100
Ian Campbell <Ian.Campbell@xxxxxxxxxx> wrote:
...
> Could GNTTABOP_setup_table return GFNs from the very top of the GFN
> space? Perhaps even above what would be architecturally valid,
> although perhaps that is incompatible with HAP. Anything above
> max_pfn would seem to be valid for the hypervisor to place "magic"
> mappings in?
Well, what's confusing me for this is that there are few max
pfn's inside the guest! The nr_pages being one for example, then
there's max_pfn in shared_info.arch. I'm not sure if these two are in
sync with max_pfn in mm/bootmem.c. Then, we would need to adjust EPT to add
these pfns there. So that may put a damper on this.
> Another approach might be to take advantage of the fact that a modern
> PV kernel will call XENMEM_memory_map to obtain an e820 describing its
> pseudo-physical address space. You could arrange for there to be some
> reserved space returned in that.
I saw e820 code last night, and wondered if this might be the best option.
I am glad you mentioned it. I am not much familiar with e820 format, so
studying it right now.
thanks,
Mukesh
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