On 23/07/2011 07:53, "Keir Fraser" <keir.xen@xxxxxxxxx
> On 22/07/2011 19:38, "Andrei Warkentin" <andreiw@xxxxxxxxxxxx
>> On Fri, Jul 22, 2011 at 11:38 AM, Keir Fraser <keir.xen@xxxxxxxxx
>>> Looks pretty decent. I wonder why you need to change get_shared_info() --
>>> the existing mapping location is unused at the time hvmloader runs, and you
>>> instead map it over the top of a page of RAM. If you want shared_info mapped
>>> elsewhere, you can map it wherever you like as soon as your BIOS payload
>>> takes over.
>> The problem is that this page lies in an unsafe for OVMF area (right
>> below 4GB). In a typical PC environment,
>> you have the firmware ROM decoding the physical address space right
>> below 4GB, and it also has a chunk (~64-128k) shadowed below 1MB for
>> legacy reasons. The EFI firmware bootstrap code is written with the
>> assumption that it can transfer control to code < 4GB that will
>> finalize the 16->PM-(>LM if 64) transitions and call C code. The
>> get_shared_info page overlaps code we copy up below 4GB. This is why
>> it was moved to a safer region.
> Okay, we can work with this easily enough.