xen/vmap: Check the page has been mapped in vm_init_type()

The function map_pages_to_xen() could fail if it can't allocate the
underlying page tables or (at least on Arm) if the area was already
mapped.

The first error is caught by clear_page() because it would fault.
However, the second error while very unlikely is not caught at all.

As this is boot code, use BUG_ON() to check if map_pages_to_xen() has
succeeded.

Signed-off-by: Julien Grall <jgrall@amazon.com>
Signed-off-by: Elias El Yandouzi <eliasely@amazon.com>
Acked-by: Jan Beulich <jbeulich@suse.com>

xen/common/vmap.c

@@ -35,8 +35,11 @@ void __init vm_init_type(enum vmap_region type, void *start, void *end)
     for ( i = 0, va = (unsigned long)vm_bitmap(type); i < nr; ++i, va += PAGE_SIZE )
     {
         struct page_info *pg = alloc_domheap_page(NULL, 0);
+        int rc;
+
+        rc = map_pages_to_xen(va, page_to_mfn(pg), 1, PAGE_HYPERVISOR);
+        BUG_ON(rc);
 
-        map_pages_to_xen(va, page_to_mfn(pg), 1, PAGE_HYPERVISOR);
         clear_page((void *)va);
     }
     bitmap_fill(vm_bitmap(type), vm_low[type]);