From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from psmtp.com (na3sys010amx195.postini.com [74.125.245.195]) by kanga.kvack.org (Postfix) with SMTP id 5E4516B0062 for ; Wed, 27 Jun 2012 15:20:33 -0400 (EDT) Date: Wed, 27 Jun 2012 20:18:01 +0100 From: Russell King - ARM Linux Subject: Re: [PATCH] [RESEND] arm: limit memblock base address for early_pte_alloc Message-ID: <20120627191801.GD25319@n2100.arm.linux.org.uk> References: <1338880312-17561-1-git-send-email-minchan@kernel.org> <025701cd457e$d5065410$7f12fc30$@lge.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <025701cd457e$d5065410$7f12fc30$@lge.com> Sender: owner-linux-mm@kvack.org List-ID: To: "Kim, Jong-Sung" Cc: 'Minchan Kim' , 'Nicolas Pitre' , 'Catalin Marinas' , linux-arm-kernel@lists.infradead.org, linux-kernel@vger.kernel.org, 'Chanho Min' , linux-mm@kvack.org On Fri, Jun 08, 2012 at 10:58:50PM +0900, Kim, Jong-Sung wrote: > > From: Minchan Kim [mailto:minchan@kernel.org] > > 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@kvack.org. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: email@kvack.org