[Xen-devel] Re: HYBRID: gnttab_map() to map shared frames..

[Mukesh Rathor <mukesh.rathor@xxxxxxxxxx>]

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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