page_alloc: clear nr_bootmem_regions in end_boot_allocator()

... to make alloc_boot_pages() fail for late callers. Don't rely on
reaching the BOOT_BUG_ON(1) near the end of that function though, but
instead make this situation easier to distinguish from actual
allocation failures by adding an explicit check.

While there, make the iteration variable unsigned and guard against
underflow.

Signed-off-by: Jan Beulich <jbeulich@suse.com>
Reviewed-by: Andrew Cooper <andrew.cooper3@citrix.com>

diff --git a/xen/common/page_alloc.c b/xen/common/page_alloc.c
index ae2476d10c1d24eda58bebdd1b44b7ab580488ec..915e1f76547ac03bba1c5b1b588ca532dc2c7ed3 100644 (file)
--- a/xen/common/page_alloc.c
+++ b/xen/common/page_alloc.c
@@ -329,13 +329,16 @@ unsigned long __init alloc_boot_pages(
     unsigned long nr_pfns, unsigned long pfn_align)
 {
     unsigned long pg, _e;
-    int i;
+    unsigned int i = nr_bootmem_regions;
 
-    for ( i = nr_bootmem_regions - 1; i >= 0; i-- )
+    BOOT_BUG_ON(!nr_bootmem_regions);
+
+    while ( i-- )
     {
         struct bootmem_region *r = &bootmem_region_list[i];
+
         pg = (r->e - nr_pfns) & ~(pfn_align - 1);
-        if ( pg < r->s )
+        if ( pg >= r->e || pg < r->s )
             continue;
 
 #if defined(CONFIG_X86) && !defined(NDEBUG)
@@ -1352,6 +1355,7 @@ void __init end_boot_allocator(void)
         if ( r->s < r->e )
             init_heap_pages(mfn_to_page(r->s), r->e - r->s);
     }
+    nr_bootmem_regions = 0;
     init_heap_pages(virt_to_page(bootmem_region_list), 1);
 
     if ( !dma_bitsize && (num_online_nodes() > 1) )