xen: patch to batch pvh/dom0 mem mapping

[alexandermerritt]

Addresses some of the latency costs identified in https://github.com/edera-dev/protect/issues/1890

Tested on native dell desktop and was measured to improve performance of zone launches by ~37ms.

[bleggett]

looks good to me and makes logical sense but I'm not an MMU expert.

[alexandermerritt]

I rewrote the patch to another branch, and attempted to simplify it more: https://github.com/edera-dev/linux-upstream/commits/alexm/mmap_batch_v2/

more recent two commits contain the changes, and in them I addressed the above comments

[alexandermerritt]

I rewrote the patch to another branch, and attempted to simplify it more: https://github.com/edera-dev/linux-upstream/commits/alexm/mmap_batch_v2/

more recent two commits contain the changes, and in them I addressed the above comments

Notably, with a more minimal change, reusing xen_for_each_gfn, I am measuring we lost 10ms to launching a zone (88ms vs 78ms with the v1), as that iterates with a callback on each page.