1 files changed, 22 insertions, 2 deletions

diff --git a/arch/x86/mm/init.c b/arch/x86/mm/init.c
index 286d289b039b..37b8b0fe8320 100644
--- a/arch/x86/mm/init.c
+++ b/arch/x86/mm/init.c
@@ -81,6 +81,11 @@ static void __init find_early_table_space(unsigned long end, int use_pse,
                 end, pgt_buf_start << PAGE_SHIFT, pgt_buf_top << PAGE_SHIFT);
 }
 
+void __init native_pagetable_reserve(u64 start, u64 end)
+{
+        memblock_x86_reserve_range(start, end, "PGTABLE");
+}
+
 struct map_range {
         unsigned long start;
         unsigned long end;
@@ -272,9 +277,24 @@ unsigned long __init_refok init_memory_mapping(unsigned long start,
 
         __flush_tlb_all();
 
+        /*
+         * Reserve the kernel pagetable pages we used (pgt_buf_start -
+         * pgt_buf_end) and free the other ones (pgt_buf_end - pgt_buf_top)
+         * so that they can be reused for other purposes.
+         *
+         * On native it just means calling memblock_x86_reserve_range, on Xen it
+         * also means marking RW the pagetable pages that we allocated before
+         * but that haven't been used.
+         *
+         * In fact on xen we mark RO the whole range pgt_buf_start -
+         * pgt_buf_top, because we have to make sure that when
+         * init_memory_mapping reaches the pagetable pages area, it maps
+         * RO all the pagetable pages, including the ones that are beyond
+         * pgt_buf_end at that time.
+         */
         if (!after_bootmem && pgt_buf_end > pgt_buf_start)
-                memblock_x86_reserve_range(pgt_buf_start << PAGE_SHIFT,
-                                 pgt_buf_end << PAGE_SHIFT, "PGTABLE");
+                x86_init.mapping.pagetable_reserve(PFN_PHYS(pgt_buf_start),
+                                PFN_PHYS(pgt_buf_end));
 
         if (!after_bootmem)
                 early_memtest(start, end);