x86/mm: drop old page table APIs

x86/mm: drop old page table APIs

Two sets of old APIs, alloc/free_xen_pagetable() and lXe_to_lYe(), are
now dropped to avoid the dependency on direct map.

There are two special cases which still have not been re-written into
the new APIs, thus need special treatment:

rpt in smpboot.c cannot use ephemeral mappings yet. The problem is that
rpt is read and written in context switch code, but the mapping
infrastructure is NOT context-switch-safe, meaning we cannot map rpt in
one domain and unmap in another. Before the mapping infrastructure
supports context switches, rpt has to be globally mapped.

Also, lXe_to_lYe() during Xen image relocation cannot be converted into
map/unmap pairs. We cannot hold on to mappings while the mapping
infrastructure is being relocated! It is enough to remove the direct map
in the second e820 pass, so we still use the direct map (<4GiB) in Xen
relocation (which is during the first e820 pass).

Signed-off-by: Wei Liu <wei.liu2@citrix.com>
Signed-off-by: Hongyan Xia <hongyxia@amazon.com>
Reviewed-by: Jan Beulich <jbeulich@suse.com>