> From: Minchan Kim [mailto:minchan@xxxxxxxxxx] > Sent: Tuesday, June 05, 2012 4:12 PM > > If we do arm_memblock_steal with a page which is not aligned with section > size, panic can happen during boot by page fault in map_lowmem. > > Detail: > > 1) mdesc->reserve can steal a page which is allocated at 0x1ffff000 by > memblock > which prefers tail pages of regions. > 2) map_lowmem maps 0x00000000 - 0x1fe00000 > 3) map_lowmem try to map 0x1fe00000 but it's not aligned by section due to 1. > 4) calling alloc_init_pte allocates a new page for new pte by memblock_alloc > 5) allocated memory for pte is 0x1fffe000 -> it's not mapped yet. > 6) memset(ptr, 0, sz) in early_alloc_aligned got PANICed! May I suggest another simple approach? The first continuous couples of sections are always safely section-mapped inside alloc_init_section funtion. So, by limiting memblock_alloc to the end of the first continuous couples of sections at the start of map_lowmem, map_lowmem can safely memblock_alloc & memset even if we have one or more section-unaligned memory regions. The limit can be extended back to arm_lowmem_limit after the map_lowmem is done. diff --git a/arch/arm/mm/mmu.c b/arch/arm/mm/mmu.c index e5dad60..edf1e2d 100644 --- a/arch/arm/mm/mmu.c +++ b/arch/arm/mm/mmu.c @@ -1094,6 +1094,11 @@ static void __init kmap_init(void) static void __init map_lowmem(void) { struct memblock_region *reg; + phys_addr_t pmd_map_end; + + pmd_map_end = (memblock.memory.regions[0].base + + memblock.memory.regions[0].size) & PMD_MASK; + memblock_set_current_limit(pmd_map_end); /* Map all the lowmem memory banks. */ for_each_memblock(memory, reg) { @@ -1113,6 +1118,8 @@ static void __init map_lowmem(void) create_mapping(&map); } + + memblock_set_current_limit(arm_lowmem_limit); } /* @@ -1123,8 +1130,6 @@ void __init paging_init(struct machine_desc *mdesc) { void *zero_page; - memblock_set_current_limit(arm_lowmem_limit); - build_mem_type_table(); prepare_page_table(); map_lowmem(); -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@xxxxxxxxx. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: <a href=mailto:"dont@xxxxxxxxx";> email@xxxxxxxxx </a>