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=-15.3 required=3.0 tests=BAYES_00, HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_CR_TRAILER,INCLUDES_PATCH, MAILING_LIST_MULTI,NICE_REPLY_A,SPF_HELO_NONE,SPF_PASS,URIBL_BLOCKED, USER_AGENT_SANE_1 autolearn=ham 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 039E1C433C1 for ; Fri, 26 Mar 2021 14:17:37 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id AFDB361A02 for ; Fri, 26 Mar 2021 14:17:36 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S230113AbhCZORF (ORCPT ); Fri, 26 Mar 2021 10:17:05 -0400 Received: from mx2.suse.de ([195.135.220.15]:43686 "EHLO mx2.suse.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S229986AbhCZORB (ORCPT ); Fri, 26 Mar 2021 10:17:01 -0400 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 D2F6FAC6A; Fri, 26 Mar 2021 14:17:00 +0000 (UTC) To: Sergei Trofimovich , Andrew Morton , linux-mm@kvack.org Cc: linux-kernel@vger.kernel.org, David Hildenbrand References: <20210326112650.307890-1-slyfox@gentoo.org> From: Vlastimil Babka Subject: Re: [PATCH] mm: page_alloc: ignore init_on_free=1 for page alloc Message-ID: <6c4a20f3-16ab-3c6c-1d6d-4708db4e9ebf@suse.cz> Date: Fri, 26 Mar 2021 15:17:00 +0100 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:78.0) Gecko/20100101 Thunderbird/78.8.1 MIME-Version: 1.0 In-Reply-To: <20210326112650.307890-1-slyfox@gentoo.org> Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: 8bit Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 3/26/21 12:26 PM, Sergei Trofimovich wrote: > init_on_free=1 does not guarantee that free pages contain only zero bytes. > > Some examples: > 1. page_poison=on takes presedence over init_on_alloc=1 / ini_on_free=1 Yes, and it spits out a message that you enabled both and poisoning takes precedence. It was that way even before my changes IIRC, but not consistent. > 2. free_pages_prepare() always poisons pages: > > if (want_init_on_free()) > kernel_init_free_pages(page, 1 << order); > kernel_poison_pages(page, 1 << order kernel_poison_pages() includes a test if poisoning is enabled. And in that case want_init_on_free() shouldn't be. see init_mem_debugging_and_hardening() > > I observed use of poisoned pages as the crash on ia64 booted with > init_on_free=1 init_on_alloc=1 (CONFIG_PAGE_POISONING=y config). > There pmd page contained 0xaaaaaaaa poison pages and led to early crash. Hm but that looks lika a sign that ia64 pmd allocation should use __GFP_ZERO and doesn't. It shouldn't rely on init_on_alloc or init_on_free being enabled. > The change drops the assumption that init_on_free=1 guarantees free > pages to contain zeros. The change assumes that page_poison=on also leaves want_init_on_free() enabled, but it doesn't. > Alternative would be to make interaction between runtime poisoning and > sanitizing options and build-time debug flags like CONFIG_PAGE_POISONING > more coherent. I took the simpler path. So that was done in 5.11 and the decisions can be seen in init_mem_debugging_and_hardening(). There might be of course a bug, or later changes broke something. Which was the version that you observed a bug? > Tested the fix on rx3600. > > CC: Andrew Morton > CC: linux-mm@kvack.org > Signed-off-by: Sergei Trofimovich > --- > mm/page_alloc.c | 2 +- > 1 file changed, 1 insertion(+), 1 deletion(-) > > diff --git a/mm/page_alloc.c b/mm/page_alloc.c > index cfc72873961d..d57d9b4f7089 100644 > --- a/mm/page_alloc.c > +++ b/mm/page_alloc.c > @@ -2301,7 +2301,7 @@ inline void post_alloc_hook(struct page *page, unsigned int order, > kernel_unpoison_pages(page, 1 << order); > set_page_owner(page, order, gfp_flags); > > - if (!want_init_on_free() && want_init_on_alloc(gfp_flags)) > + if (want_init_on_alloc(gfp_flags)) > kernel_init_free_pages(page, 1 << order); > } > >