From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752173AbdHHLus (ORCPT ); Tue, 8 Aug 2017 07:50:48 -0400 Received: from aserp1040.oracle.com ([141.146.126.69]:29116 "EHLO aserp1040.oracle.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751925AbdHHLuq (ORCPT ); Tue, 8 Aug 2017 07:50:46 -0400 Subject: Re: [v6 11/15] arm64/kasan: explicitly zero kasan shadow memory To: Will Deacon Cc: linux-kernel@vger.kernel.org, sparclinux@vger.kernel.org, linux-mm@kvack.org, linuxppc-dev@lists.ozlabs.org, linux-s390@vger.kernel.org, linux-arm-kernel@lists.infradead.org, x86@kernel.org, kasan-dev@googlegroups.com, borntraeger@de.ibm.com, heiko.carstens@de.ibm.com, davem@davemloft.net, willy@infradead.org, mhocko@kernel.org, ard.biesheuvel@linaro.org, catalin.marinas@arm.com, sam@ravnborg.org References: <1502138329-123460-1-git-send-email-pasha.tatashin@oracle.com> <1502138329-123460-12-git-send-email-pasha.tatashin@oracle.com> <20170808090743.GA12887@arm.com> From: Pasha Tatashin Message-ID: Date: Tue, 8 Aug 2017 07:49:22 -0400 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:52.0) Gecko/20100101 Thunderbird/52.2.1 MIME-Version: 1.0 In-Reply-To: <20170808090743.GA12887@arm.com> Content-Type: text/plain; charset=utf-8; format=flowed Content-Language: en-US Content-Transfer-Encoding: 7bit X-Source-IP: aserv0022.oracle.com [141.146.126.234] Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Hi Will, Thank you for looking at this change. What you described was in my previous iterations of this project. See for example here: https://lkml.org/lkml/2017/5/5/369 I was asked to remove that flag, and only zero memory in place when needed. Overall the current approach is better everywhere else in the kernel, but it adds a little extra code to kasan initialization. Pasha On 08/08/2017 05:07 AM, Will Deacon wrote: > On Mon, Aug 07, 2017 at 04:38:45PM -0400, Pavel Tatashin wrote: >> To optimize the performance of struct page initialization, >> vmemmap_populate() will no longer zero memory. >> >> We must explicitly zero the memory that is allocated by vmemmap_populate() >> for kasan, as this memory does not go through struct page initialization >> path. >> >> Signed-off-by: Pavel Tatashin >> Reviewed-by: Steven Sistare >> Reviewed-by: Daniel Jordan >> Reviewed-by: Bob Picco >> --- >> arch/arm64/mm/kasan_init.c | 42 ++++++++++++++++++++++++++++++++++++++++++ >> 1 file changed, 42 insertions(+) >> >> diff --git a/arch/arm64/mm/kasan_init.c b/arch/arm64/mm/kasan_init.c >> index 81f03959a4ab..e78a9ecbb687 100644 >> --- a/arch/arm64/mm/kasan_init.c >> +++ b/arch/arm64/mm/kasan_init.c >> @@ -135,6 +135,41 @@ static void __init clear_pgds(unsigned long start, >> set_pgd(pgd_offset_k(start), __pgd(0)); >> } >> >> +/* >> + * Memory that was allocated by vmemmap_populate is not zeroed, so we must >> + * zero it here explicitly. >> + */ >> +static void >> +zero_vmemmap_populated_memory(void) >> +{ >> + struct memblock_region *reg; >> + u64 start, end; >> + >> + for_each_memblock(memory, reg) { >> + start = __phys_to_virt(reg->base); >> + end = __phys_to_virt(reg->base + reg->size); >> + >> + if (start >= end) >> + break; >> + >> + start = (u64)kasan_mem_to_shadow((void *)start); >> + end = (u64)kasan_mem_to_shadow((void *)end); >> + >> + /* Round to the start end of the mapped pages */ >> + start = round_down(start, SWAPPER_BLOCK_SIZE); >> + end = round_up(end, SWAPPER_BLOCK_SIZE); >> + memset((void *)start, 0, end - start); >> + } >> + >> + start = (u64)kasan_mem_to_shadow(_text); >> + end = (u64)kasan_mem_to_shadow(_end); >> + >> + /* Round to the start end of the mapped pages */ >> + start = round_down(start, SWAPPER_BLOCK_SIZE); >> + end = round_up(end, SWAPPER_BLOCK_SIZE); >> + memset((void *)start, 0, end - start); >> +} > > I can't help but think this would be an awful lot nicer if you made > vmemmap_alloc_block take extra GFP flags as a parameter. That way, we could > implement a version of vmemmap_populate that does the zeroing when we need > it, without having to duplicate a bunch of the code like this. I think it > would also be less error-prone, because you wouldn't have to do the > allocation and the zeroing in two separate steps. > > Will >