xtensa: nommu: reserve memory below PLATFORM_DEFAULT_MEM_START

Memory accounting code can't handle pages below
PLATFORM_DEFAULT_MEM_START. Reserve those pages if they exist.
When PLATFORM_DEFAULT_MEM_START is zero reserve one page at address 0 to
make sure that successfull memory allocations don't return NULL.

Signed-off-by: Max Filippov <jcmvbkbc@gmail.com>

1 files changed, 11 insertions, 0 deletions

diff --git a/arch/xtensa/mm/init.c b/arch/xtensa/mm/init.c
index 77ed20209ca5..5a084fa5b608 100644
--- a/arch/xtensa/mm/init.c
+++ b/arch/xtensa/mm/init.c
@@ -239,6 +239,17 @@ void __init bootmem_init(void)
         unsigned long bootmap_start, bootmap_size;
         int i;
 
+        /* Reserve all memory below PLATFORM_DEFAULT_MEM_START, as memory
+         * accounting doesn't work for pages below that address.
+         *
+         * If PLATFORM_DEFAULT_MEM_START is zero reserve page at address 0:
+         * successfull allocations should never return NULL.
+         */
+        if (PLATFORM_DEFAULT_MEM_START)
+                mem_reserve(0, PLATFORM_DEFAULT_MEM_START, 0);
+        else
+                mem_reserve(0, 1, 0);
+
         sysmem_dump();
         max_low_pfn = max_pfn = 0;
         min_low_pfn = ~0;