memblock: make free_reserved_area() more robust

memblock: make free_reserved_area() more robust

There are two potential problems in free_reserved_area():
* it may free a page with not-existent buddy page
* it may be passed a virtual address from an alias mapping that won't
  be properly translated by virt_to_page(), for example a symbol on arm64

While first issue is quite theoretical and the second one does not manifest
itself because all the callers do the right thing, it is easy to make
free_reserved_area() robust enough to avoid these potential issues.

Replace the loop by virtual address with a loop by pfn that uses
for_each_valid_pfn() and use __pa() or __pa_symbol() depending on the
virtual mapping alias to correctly determine the loop boundaries.

Link: https://patch.msgid.link/20260323074836.3653702-6-rppt@kernel.org
Signed-off-by: Mike Rapoport (Microsoft) <rppt@kernel.org>