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 0AB7AC38A02 for ; Wed, 26 Oct 2022 03:03:19 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S232926AbiJZDDS (ORCPT ); Tue, 25 Oct 2022 23:03:18 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:53628 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S232824AbiJZDC2 (ORCPT ); Tue, 25 Oct 2022 23:02:28 -0400 Received: from szxga02-in.huawei.com (szxga02-in.huawei.com [45.249.212.188]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 0155096A02 for ; Tue, 25 Oct 2022 20:01:19 -0700 (PDT) Received: from dggpemm500024.china.huawei.com (unknown [172.30.72.55]) by szxga02-in.huawei.com (SkyGuard) with ESMTP id 4Mxtk714sJzVj2d; Wed, 26 Oct 2022 10:56:31 +0800 (CST) Received: from dggpemm500014.china.huawei.com (7.185.36.153) by dggpemm500024.china.huawei.com (7.185.36.203) with Microsoft SMTP Server (version=TLS1_2, cipher=TLS_ECDHE_RSA_WITH_AES_128_GCM_SHA256) id 15.1.2375.31; Wed, 26 Oct 2022 11:01:18 +0800 Received: from [10.174.178.120] (10.174.178.120) by dggpemm500014.china.huawei.com (7.185.36.153) with Microsoft SMTP Server (version=TLS1_2, cipher=TLS_ECDHE_RSA_WITH_AES_128_GCM_SHA256) id 15.1.2375.31; Wed, 26 Oct 2022 11:01:17 +0800 Message-ID: <1b2e03b2-5e91-2e60-82d0-ea111840c81d@huawei.com> Date: Wed, 26 Oct 2022 11:01:17 +0800 MIME-Version: 1.0 User-Agent: Mozilla/5.0 (Windows NT 10.0; Win64; x64; rv:102.0) Gecko/20100101 Thunderbird/102.3.2 CC: , , , , , , , , Subject: Re: [PATCH -next 1/1] mm: hugetlb_vmemmap: Fix WARN_ON in vmemmap_remap_pte Content-Language: en-US To: References: <20221025014215.3466904-1-mawupeng1@huawei.com> <614E3E83-1EAB-4C39-AF9C-83C0CCF26218@linux.dev> From: mawupeng In-Reply-To: <614E3E83-1EAB-4C39-AF9C-83C0CCF26218@linux.dev> Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: 8bit X-Originating-IP: [10.174.178.120] X-ClientProxiedBy: dggems705-chm.china.huawei.com (10.3.19.182) To dggpemm500014.china.huawei.com (7.185.36.153) X-CFilter-Loop: Reflected Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 2022/10/25 14:36, Muchun Song wrote: > > >> On Oct 25, 2022, at 09:42, Wupeng Ma wrote: >> >> From: Ma Wupeng >> >> Commit f41f2ed43ca5 ("mm: hugetlb: free the vmemmap pages associated with >> each HugeTLB page") add vmemmap_remap_pte to remap the tail pages as >> read-only to catch illegal write operation to the tail page. >> >> However this will lead to WARN_ON in arm64 in __check_racy_pte_update() > > Thanks for your finding this issue. > >> since this may lead to dirty state cleaned. This check is introduced by >> commit 2f4b829c625e ("arm64: Add support for hardware updates of the >> access and dirty pte bits") and the initial check is as follow: >> >> BUG_ON(pte_write(*ptep) && !pte_dirty(pte)); >> >> Since we do need to mark this pte as read-only to catch illegal write >> operation to the tail pages, use set_pte to replace set_pte_at to bypass >> this check. > > In theory, the waring does not affect anything since the tail vmemmap > pages are supposed to be read-only. So, skipping this check for vmemmap > pages seem feasible. But I am not sure whether it is general to use > set_pte here instead of set_pte_at, I didn’t see any users of set_pte > from the common code routines except the code from arch/xxx. And this > issue is specific for arm64, so I suggest fixing it in __check_racy_pte_update() > itself. > > Something like (Just some thoughts from mine): > > diff --git a/arch/arm64/include/asm/pgtable.h b/arch/arm64/include/asm/pgtable.h > index b5df82aa99e6..df7716965a93 100644 > --- a/arch/arm64/include/asm/pgtable.h > +++ b/arch/arm64/include/asm/pgtable.h > @@ -292,7 +292,8 @@ extern void __sync_icache_dcache(pte_t pteval); > * PTE_DIRTY || (PTE_WRITE && !PTE_RDONLY) > */ > > -static inline void __check_racy_pte_update(struct mm_struct *mm, pte_t *ptep, > +static inline void __check_racy_pte_update(struct mm_struct *mm, > + unsigned long addr, pte_t *ptep, > pte_t pte) > { > pte_t old_pte; > @@ -307,6 +308,10 @@ static inline void __check_racy_pte_update(struct mm_struct *mm, pte_t *ptep, > if (mm != current->active_mm && atomic_read(&mm->mm_users) <= 1) > return; > > + if (IS_ENABLED(CONFIG_HUGETLB_PAGE_OPTIMIZE_VMEMMAP) && > + addr >= VMEMMAP_START && addr <= VMEMMAP_END) > + return; > + > /* > * Check for potential race with hardware updates of the pte > * (ptep_set_access_flags safely changes valid ptes without going > >> >> The following shell command can be used to reproduce this WARN_ON in >> 6.1.0-rc1: >> >> echo 1 > /proc/sys/vm/hugetlb_optimize_vmemmap >> cat /proc/sys/vm/hugetlb_optimize_vmemmap >> >> echo 1024 > /proc/sys/vm/nr_overcommit_hugepages >> mkdir -p /root/hugetlb >> mount none /root/hugetlb -t hugetlbfs >> fallocate -l 2g /root/hugetlb/xx & >> >> Here is the detail WARN_ON log: >> >> ------------[ cut here ]------------ >> __check_racy_pte_update: racy dirty state clearing: 0x0068000416899f03 -> 0x0060000416898f83 >> WARNING: CPU: 3 PID: 394 at arch/arm64/include/asm/pgtable.h:318 vmemmap_remap_pte+0x118/0x120 >> Modules linked in: >> CPU: 3 PID: 394 Comm: fallocate Not tainted 6.1.0-rc1 #224 >> Hardware name: QEMU QEMU Virtual Machine, BIOS 0.0.0 02/06/2015 >> Call trace: >> vmemmap_remap_pte+0x118/0x120 >> vmemmap_remap_range+0x30c/0x560 >> hugetlb_vmemmap_optimize+0x158/0x408 >> __prep_new_huge_page+0x24/0x150 >> prep_new_huge_page+0x30/0x60 >> alloc_fresh_huge_page+0x1c4/0x1e0 >> alloc_surplus_huge_page+0xa0/0x168 >> alloc_huge_page+0x264/0x5b8 >> hugetlbfs_fallocate+0x294/0x680 >> vfs_fallocate+0x12c/0x568 >> ksys_fallocate+0x50/0xa0 >> __arm64_sys_fallocate+0x28/0x38 >> invoke_syscall+0x4c/0x110 >> el0_svc_common.constprop.0+0x68/0x128 >> do_el0_svc+0x34/0xd0 >> el0_svc+0x48/0xb8 >> el0t_64_sync_handler+0xb8/0xc0 >> el0t_64_sync+0x18c/0x190 >> ---[ end trace 0000000000000000 ]--- >> >> Fixes: f41f2ed43ca5 ("mm: hugetlb: free the vmemmap pages associated with each HugeTLB page") > > Actually, this commit does not pose the issue for arm64. I think the correct commit > which should be fixed is 1e63ac088f20f7a4425c430c31ecd3cf167fb3f2. > > Thanks. Thanks for pointing it out. I have tested the commit, it sure is patch 1e63ac088f20f7a4425c430c31ecd3cf167fb3f2. This VM_WARN_ONCE will be produced if HUGETLB_PAGE_FREE_VMEMMAP for arm64 is enabled. I will change my change log and fix this in next patch. > >> Signed-off-by: Ma Wupeng >> --- >> mm/hugetlb_vmemmap.c | 2 +- >> 1 file changed, 1 insertion(+), 1 deletion(-) >> >> diff --git a/mm/hugetlb_vmemmap.c b/mm/hugetlb_vmemmap.c >> index ba2a2596fb4e..cb056265c31e 100644 >> --- a/mm/hugetlb_vmemmap.c >> +++ b/mm/hugetlb_vmemmap.c >> @@ -249,7 +249,7 @@ static void vmemmap_remap_pte(pte_t *pte, unsigned long addr, >> struct page *page = pte_page(*pte); >> >> list_add_tail(&page->lru, walk->vmemmap_pages); >> - set_pte_at(&init_mm, addr, pte, entry); >> + set_pte(pte, entry); >> } >> >> /* >> -- >> 2.25.1 >> >> >