On Fri, Jun 08, 2012 at 10:58:50PM +0900, Kim, Jong-Sung wrote: > > 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. No. What if the first block of memory is not large enough to handle all the allocations? I think the real problem is folk trying to reserve small amounts. I have said all reservations must be aligned to 1MB. -- 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>