public/elfnote: document non-alignment of relocated init-P2M

Since PV kernels can't use large pages anywa, when the init-P2M support
was added it was decided to keep the implementation simple and not
align large pages in PFN space. Document this.

Signed-off-by: Jan Beulich <jbeulich@xxxxxxxx>

--- a/xen/include/public/elfnote.h
+++ b/xen/include/public/elfnote.h
@@ -173,7 +173,9 @@
  * The (non-default) location the initial phys-to-machine map should be
  * placed at by the hypervisor (Dom0) or the tools (DomU).
  * The kernel must be prepared for this mapping to be established using
- * large pages, despite such otherwise not being available to guests.
+ * large pages, despite such otherwise not being available to guests. Note
+ * that these large pages may be misaligned in PFN space (they'll obviously
+ * be aligned in MFN and virtual address spaces).
  * The kernel must also be able to handle the page table pages used for
  * this mapping not being accessible through the initial mapping.
  * (Only x86-64 supports this at present.)