[PATCH 4/6] x86/mem-paging: add minimal lock order enforcement to p2m_mem_paging_prep()

[Jan Beulich <jbeulich@xxxxxxxx>]

While full checking is impossible (as the lock is being acquired/
released down the call tree), perform at least a lock level check.

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

--- a/xen/arch/x86/mm/p2m.c
+++ b/xen/arch/x86/mm/p2m.c
@@ -1813,6 +1813,7 @@ int p2m_mem_paging_prep(struct domain *d
             goto out;
         /* Get a free page */
         ret = -ENOMEM;
+        page_alloc_mm_pre_lock(d);
         page = alloc_domheap_page(d, 0);
         if ( unlikely(page == NULL) )
             goto out;