x86/mem-sharing: mem-sharing a range of memory

x86/mem-sharing: mem-sharing a range of memory

Currently mem-sharing can be performed on a page-by-page basis from the control
domain. However, this process is quite wasteful when a range of pages have to
be deduplicated.

This patch introduces a new mem_sharing memop for range sharing where
the user doesn't have to separately nominate each page in both the source and
destination domain, and the looping over all pages happen in the hypervisor.
This significantly reduces the overhead of sharing a range of memory.

Signed-off-by: Tamas K Lengyel <tamas.lengyel@zentific.com>
Acked-by: Wei Liu <wei.liu2@citrix.com>
Reviewed-by: Andrew Cooper <andrew.cooper3@citrix.com>