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 Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id 19B07C433FE for ; Wed, 20 Apr 2022 13:53:05 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S235668AbiDTNzt (ORCPT ); Wed, 20 Apr 2022 09:55:49 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:44074 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1354174AbiDTNzs (ORCPT ); Wed, 20 Apr 2022 09:55:48 -0400 Received: from ams.source.kernel.org (ams.source.kernel.org [IPv6:2604:1380:4601:e00::1]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 6276A3ED27; Wed, 20 Apr 2022 06:53:01 -0700 (PDT) Received: from smtp.kernel.org (relay.kernel.org [52.25.139.140]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by ams.source.kernel.org (Postfix) with ESMTPS id 1D021B81D6E; Wed, 20 Apr 2022 13:53:00 +0000 (UTC) Received: by smtp.kernel.org (Postfix) with ESMTPSA id 6DFDEC385A0; Wed, 20 Apr 2022 13:52:53 +0000 (UTC) Message-ID: <6f56d0d6-6d0d-f0c9-87df-f3ff25b26fc5@linux-m68k.org> Date: Wed, 20 Apr 2022 23:52:50 +1000 MIME-Version: 1.0 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:91.0) Gecko/20100101 Thunderbird/91.7.0 Subject: Re: Regression with v5.18-rc1 tag on STM32F7 and STM32H7 based boards Content-Language: en-US To: Hugh Dickins , Patrice CHOTARD Cc: Arnd Bergmann , mpatocka@redhat.com, lczerner@redhat.com, djwong@kernel.org, hch@lst.de, zkabelac@redhat.com, miklos@szeredi.hu, bp@suse.de, akpm@linux-foundation.org, Alexandre TORGUE - foss , Valentin CARON - foss , linux-stm32@st-md-mailman.stormreply.com, linux-kernel@vger.kernel.org, linux-fsdevel@vger.kernel.org, linux-mm@kvack.org, linux-arch@vger.kernel.org, linux-arm-kernel@lists.infradead.org, uclinux-h8-devel@lists.sourceforge.jp, linux-m68k@lists.linux-m68k.org, Geert Uytterhoeven , Yoshinori Sato , Russell King References: <481a13f8-d339-f726-0418-ab4258228e91@foss.st.com> <95a0d1dd-bcce-76c7-97b9-8374c9913321@google.com> <7f2993a9-adc5-2b90-9218-c4ca8239c3e@google.com> <3695dc2a-7518-dee4-a647-821c7cda4a0f@foss.st.com> <2a462b23-5b8e-bbf4-ec7d-778434a3b9d7@google.com> From: Greg Ungerer In-Reply-To: <2a462b23-5b8e-bbf4-ec7d-778434a3b9d7@google.com> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit Precedence: bulk List-ID: X-Mailing-List: linux-arch@vger.kernel.org Hi Hugh, On 16/4/22 10:58, Hugh Dickins wrote: > On Wed, 6 Apr 2022, Patrice CHOTARD wrote: >> On 4/6/22 08:22, Hugh Dickins wrote: >>> Asking Arnd and others below: should noMMU arches have a good ZERO_PAGE? >>> >>> On Tue, 5 Apr 2022, Hugh Dickins wrote: >>>> On Tue, 5 Apr 2022, Patrice CHOTARD wrote: >>>>> >>>>> We found an issue with last kernel tag v5.18-rc1 on stm32f746-disco and >>>>> stm32h743-disco boards (ARMV7-M SoCs). >>>>> >>>>> Kernel hangs when executing SetPageUptodate(ZERO_PAGE(0)); in mm/filemap.c. >>>>> >>>>> By reverting commit 56a8c8eb1eaf ("tmpfs: do not allocate pages on read"), >>>>> kernel boots without any issue. >>>> >>>> Sorry about that, thanks a lot for finding. >>>> >>>> I see that arch/arm/configs/stm32_defconfig says CONFIG_MMU is not set: >>>> please confirm that is the case here. >>>> >>>> Yes, it looks as if NOMMU platforms are liable to have a bogus (that's my >>>> reading, but it may be unfair) definition for ZERO_PAGE(vaddr), and I was >>>> walking on ice to touch it without regard for !CONFIG_MMU. >>>> >>>> CONFIG_SHMEM depends on CONFIG_MMU, so that PageUptodate is only needed >>>> when CONFIG_MMU. >>>> >>>> Easily fixed by an #ifdef CONFIG_MMU there in mm/filemap.c, but I'll hunt >>>> around (again) for a better place to do it - though I won't want to touch >>>> all the architectures for it. I'll post later today. >>> >>> I could put #ifdef CONFIG_MMU around the SetPageUptodate(ZERO_PAGE(0)) >>> added to pagecache_init(); or if that's considered distasteful, I could >>> skip making it potentially useful to other filesystems, revert the change >>> to pagecache_init(), and just do it in mm/shmem.c's CONFIG_SHMEM (hence >>> CONFIG_MMU) instance of shmem_init(). >>> >>> But I wonder if it's safe for noMMU architectures to go on without a >>> working ZERO_PAGE(0). It has uses scattered throughout the tree, in >>> drivers, fs, crypto and more, and it's not at all obvious (to me) that >>> they all depend on CONFIG_MMU. Some might cause (unreported) crashes, >>> some might use an unzeroed page in place of a pageful of zeroes. >>> >>> arm noMMU and h8300 noMMU and m68k noMMU each has >>> #define ZERO_PAGE(vaddr) (virt_to_page(0)) >>> which seems riskily wrong to me. >>> >>> h8300 and m68k actually go to the trouble of allocating an empty_zero_page >>> for this, but then forget to link it up to the ZERO_PAGE(vaddr) definition, >>> which is what all the common code uses. >>> >>> arm noMMU does not presently allocate such a page; and I do not feel >>> entitled to steal a page from arm noMMU platforms, for a hypothetical >>> case, without agreement. >>> >>> But here's an unbuilt and untested patch for consideration - which of >>> course should be split in three if agreed (and perhaps the h8300 part >>> quietly forgotten if h8300 is already on its way out). >>> >>> (Yes, arm uses empty_zero_page in a different way from all the other >>> architectures; but that's okay, and I think arm's way, with virt_to_page() >>> already baked in, is better than the others; but I've no wish to get into >>> changing them.) >>> >>> Patrice, does this patch build and run for you? I have no appreciation >>> of arm early startup issues, and may have got it horribly wrong. >> >> This patch is okay on my side on both boards (STM32F7 and STM32H7), boot are OK. >> >> Thanks for your reactivity ;-) >> Patrice > > Just to wrap up this thread: the tentative arch/ patches below did not > go into 5.18-rc2, but 5.18-rc3 will contain > 1bdec44b1eee ("tmpfs: fix regressions from wider use of ZERO_PAGE") > which fixes a further issue, and deletes the line which gave you trouble. > > With arch/h8300 removed from linux-next, and arch/arm losing a page by > the patch below, I don't think it's worth my arguing for those changes. > I'd still prefer arch/m68k to expose its empty_zero_page in ZERO_PAGE(), > or else not allocate it; but I won't be pursuing this further. Thanks for pointing this out. It certainly does look wrong to me for the m68k nommu case. I am not aware of any existing issues caused by this - but there is no good reason not to fix it. So I propose this change. Build and run tested on my m68knommu targets. Regards Greg From f809fb8fbca9e5e637b8fda380955bd799bb3926 Mon Sep 17 00:00:00 2001 From: Greg Ungerer Date: Wed, 20 Apr 2022 23:27:47 +1000 Subject: [PATCH] m68knommu: set ZERO_PAGE() allocated zeroed page The non-MMU m68k pagetable ZERO_PAGE() macro is being set to the somewhat non-sensical value of "virt_to_page(0)". The zeroth page is not in any way guaranteed to be a page full of "0". So the result is that ZERO_PAGE() will almost certainly contain random values. We already allocate a real "empty_zero_page" in the mm setup code shared between MMU m68k and non-MMU m68k. It is just not hooked up to the ZERO_PAGE() macro for the non-MMU m68k case. Fix ZERO_PAGE() to use the allocated "empty_zero_page" pointer. I am not aware of any specific issues caused by the old code. Link: https://lore.kernel.org/linux-m68k/2a462b23-5b8e-bbf4-ec7d-778434a3b9d7@google.com/T/#t Reported-by: Hugh Dickens Signed-off-by: Greg Ungerer --- arch/m68k/include/asm/pgtable_no.h | 3 ++- 1 file changed, 2 insertions(+), 1 deletion(-) diff --git a/arch/m68k/include/asm/pgtable_no.h b/arch/m68k/include/asm/pgtable_no.h index 87151d67d91e..bce5ca56c388 100644 --- a/arch/m68k/include/asm/pgtable_no.h +++ b/arch/m68k/include/asm/pgtable_no.h @@ -42,7 +42,8 @@ extern void paging_init(void); * ZERO_PAGE is a global shared page that is always zero: used * for zero-mapped memory areas etc.. */ -#define ZERO_PAGE(vaddr) (virt_to_page(0)) +extern void *empty_zero_page; +#define ZERO_PAGE(vaddr) (virt_to_page(empty_zero_page)) /* * All 32bit addresses are effectively valid for vmalloc... -- 2.25.1