Re: [Xen-devel] fixed location of share info page in HVM guests

[Keir Fraser <keir.xen@xxxxxxxxx>]

On 28/08/2012 09:23, "Olaf Hering" <olaf@xxxxxxxxx> wrote:

> On Tue, Aug 28, Keir Fraser wrote:
> 
>> How about we guarantee that guests can use the 1MB in address range
>> 0xFED00000-0xFEDFFFFF for whatever mappings they like, guaranteed unused (or
>> at least, mapped with nothing useful) when guest kernel starts?
>> 
>> This is already, and has always been, the case. But we can etch it in stone
>> quite easily. :)
> 
> 0xFED00000UL is appearently the hpet base adress. But if there is room
> after that, then lets use that. However, I'm not familiar with these
> things. Should the area appear in the E820 map as reserverd? If so,
> where is the code which configures the guests E820 map?

Okay, that was a bit too clever, trying to hide between IOAPIC and LAPIC
pages. How about a bit lower in memory -- FE700000-FE7FFFFF?

Everything in range FC000000-FFFFFFFF should already be marked
E820_RESERVED. You can test that, and also see
tools/firmware/hvmloader/e820.c:build_e820_table() (and note that
RESERVED_MEMBASE == FC000000).

Can document in hvmloader/config.h and have mem_alloc() test against it
rather than hvm_info->reserved_mem_pgstart.

 -- Keir

> Olaf



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