expand x86 arch_shared_info to support linear p2m list

expand x86 arch_shared_info to support linear p2m list

The x86 struct arch_shared_info field pfn_to_mfn_frame_list_list
currently contains the mfn of the top level page frame of the 3 level
p2m tree, which is used by the Xen tools during saving and restoring
(and live migration) of pv domains and for crash dump analysis. With
three levels of the p2m tree it is possible to support up to 512 GB of
RAM for a 64 bit pv domain.

A 32 bit pv domain can support more, as each memory page can hold 1024
instead of 512 entries, leading to a limit of 4 TB.

To be able to support more RAM on x86-64 switch to an additional
virtual mapped p2m list.

This patch expands struct arch_shared_info with a new p2m list virtual
address, the root of the page table root and a p2m generation count.
The new information is indicated by the domain to be valid by storing
a non-zero value into the page table root member.

Signed-off-by: Juergen Gross <jgross@suse.com>
Reviewed-by: Andrew Cooper <andrew.cooper3@citrix.com>