From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-5.3 required=3.0 tests=BAYES_00, HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,NICE_REPLY_A,SPF_HELO_NONE, SPF_PASS,USER_AGENT_SANE_1 autolearn=no autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id B398CC388F9 for ; Wed, 11 Nov 2020 09:58:18 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 5BBFB20729 for ; Wed, 11 Nov 2020 09:58:18 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1727346AbgKKJ6R (ORCPT ); Wed, 11 Nov 2020 04:58:17 -0500 Received: from mx2.suse.de ([195.135.220.15]:59556 "EHLO mx2.suse.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1725870AbgKKJ6P (ORCPT ); Wed, 11 Nov 2020 04:58:15 -0500 X-Virus-Scanned: by amavisd-new at test-mx.suse.de Received: from relay2.suse.de (unknown [195.135.221.27]) by mx2.suse.de (Postfix) with ESMTP id 04BB2AC23; Wed, 11 Nov 2020 09:58:14 +0000 (UTC) To: David Hildenbrand , Michal Hocko Cc: linux-kernel@vger.kernel.org, linux-mm@kvack.org, Andrew Morton , Alexander Potapenko , Mike Kravetz , Mike Rapoport , Oscar Salvador , Kees Cook , Michael Ellerman References: <20201110193240.25401-1-david@redhat.com> <20201111084738.GT12240@dhcp22.suse.cz> <4ebc711e-7fbc-62aa-b88f-3d6ffa9379ff@redhat.com> From: Vlastimil Babka Subject: Re: [PATCH v1] mm/page_alloc: clear pages in alloc_contig_pages() with init_on_alloc=1 or __GFP_ZERO Message-ID: Date: Wed, 11 Nov 2020 10:58:13 +0100 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:78.0) Gecko/20100101 Thunderbird/78.4.0 MIME-Version: 1.0 In-Reply-To: <4ebc711e-7fbc-62aa-b88f-3d6ffa9379ff@redhat.com> Content-Type: text/plain; charset=utf-8; format=flowed Content-Language: en-US Content-Transfer-Encoding: 8bit Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 11/11/20 10:06 AM, David Hildenbrand wrote: > On 11.11.20 09:47, Michal Hocko wrote: >> On Tue 10-11-20 20:32:40, David Hildenbrand wrote: >>> commit 6471384af2a6 ("mm: security: introduce init_on_alloc=1 and >>> init_on_free=1 boot options") resulted with init_on_alloc=1 in all pages >>> leaving the buddy via alloc_pages() and friends to be >>> initialized/cleared/zeroed on allocation. >>> >>> However, the same logic is currently not applied to >>> alloc_contig_pages(): allocated pages leaving the buddy aren't cleared >>> with init_on_alloc=1 and init_on_free=0. Let's also properly clear >>> pages on that allocation path and add support for __GFP_ZERO. >> >> AFAIR we do not have any user for __GFP_ZERO right? Not that this is > > Sorry, I had extended information under "---" but accidentally > regenerated the patch before sending it out. > > __GFP_ZERO is not used yet. It's intended to be used in > https://lkml.kernel.org/r/20201029162718.29910-1-david@redhat.com > and I can move that change into a separate patch if desired. > >> harmful but it is better to call that explicitly because a missing >> implementation would be a real problem and as such a bug fix. >> >> I am also not sure handling init_on_free at the higher level is good. >> As we have discussed recently the primary point of this feature is to >> add clearing at very few well defined entry points rather than spill it over >> many places. In this case the entry point for the allocator is >> __isolate_free_page which removes pages from the page allocator. I >> haven't checked how much this is used elsewhere but I would expect >> init_on_alloc to be handled there. > > Well, this is the entry point to our range allocator, which lives in > page_alloc.c - used by actual high-level allocators (CMA, gigantic > pages, etc). It's just a matter of taste where we want to have that > handling exactly inside our allocator. I agree alloc_contig_range() is fine as an entry point. > isolate_freepages_range()->split_map_pages() does the post_alloc_hook > call. As we certainly don't want to zero pages during compaction, we > could either pass the gfp_mask/"bool clear" down to that functions and > handle it in there, or handle it in isolate_freepages_range(), after the > ->split_map_pages() call. Whatever you prefer. I'd rather not put it in post_alloc_hook() where the bool would then get checked from allocator fast path as well. Maybe split_map_page() then as it contains a for-cycle already. > Thanks! >