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 90DD5C04A95 for ; Tue, 25 Oct 2022 06:36:50 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S230158AbiJYGgs (ORCPT ); Tue, 25 Oct 2022 02:36:48 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:34988 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S229491AbiJYGgn (ORCPT ); Tue, 25 Oct 2022 02:36:43 -0400 Received: from out2.migadu.com (out2.migadu.com [IPv6:2001:41d0:2:aacc::]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id B813A107CF0 for ; Mon, 24 Oct 2022 23:36:41 -0700 (PDT) Content-Type: text/plain; charset=utf-8 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linux.dev; s=key1; t=1666679800; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version:content-type:content-type: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references; bh=TNfH4Na6tLqevIRQ3qGFBgJgqk9m6+FNugR3w29RlFI=; b=RHocQ+N6kzm6Sqc1c01aNKayp9SthUiCoiPu94Y7yT5Y9aE9VP+8zrKxdyzRhdtVAKCHua U70Zy6xVWsNXZjyAB+nGUBq10aZHuMGmnQfJYhqSRkq5JVvHWsZc/N/USNSlf8L8qM3G7q gmv6ka3ep6rwZuYVH83Rrg8b9ajaig8= Mime-Version: 1.0 (Mac OS X Mail 16.0 \(3731.200.110.1.12\)) Subject: Re: [PATCH -next 1/1] mm: hugetlb_vmemmap: Fix WARN_ON in vmemmap_remap_pte X-Report-Abuse: Please report any abuse attempt to abuse@migadu.com and include these headers. From: Muchun Song In-Reply-To: <20221025014215.3466904-1-mawupeng1@huawei.com> Date: Tue, 25 Oct 2022 14:36:19 +0800 Cc: Andrew Morton , Mike Kravetz , Muchun Song , Michal Hocko , Oscar Salvador , catalin.marinas@arm.com, Linux Memory Management List , linux-kernel@vger.kernel.org Content-Transfer-Encoding: quoted-printable Message-Id: <614E3E83-1EAB-4C39-AF9C-83C0CCF26218@linux.dev> References: <20221025014215.3466904-1-mawupeng1@huawei.com> To: Wupeng Ma X-Migadu-Flow: FLOW_OUT Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org > On Oct 25, 2022, at 09:42, Wupeng Ma wrote: >=20 > From: Ma Wupeng >=20 > 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. >=20 > 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: >=20 > BUG_ON(pte_write(*ptep) && !pte_dirty(pte)); >=20 > 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=E2=80=99t 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 !=3D current->active_mm && atomic_read(&mm->mm_users) <=3D = 1) return; + if (IS_ENABLED(CONFIG_HUGETLB_PAGE_OPTIMIZE_VMEMMAP) && + addr >=3D VMEMMAP_START && addr <=3D VMEMMAP_END) + return; + /* * Check for potential race with hardware updates of the pte * (ptep_set_access_flags safely changes valid ptes without = going >=20 > The following shell command can be used to reproduce this WARN_ON in > 6.1.0-rc1: >=20 > echo 1 > /proc/sys/vm/hugetlb_optimize_vmemmap > cat /proc/sys/vm/hugetlb_optimize_vmemmap >=20 > echo 1024 > /proc/sys/vm/nr_overcommit_hugepages > mkdir -p /root/hugetlb > mount none /root/hugetlb -t hugetlbfs > fallocate -l 2g /root/hugetlb/xx & >=20 > Here is the detail WARN_ON log: >=20 > ------------[ 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 ]--- >=20 > 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. > Signed-off-by: Ma Wupeng > --- > mm/hugetlb_vmemmap.c | 2 +- > 1 file changed, 1 insertion(+), 1 deletion(-) >=20 > 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 =3D pte_page(*pte); >=20 > list_add_tail(&page->lru, walk->vmemmap_pages); > - set_pte_at(&init_mm, addr, pte, entry); > + set_pte(pte, entry); > } >=20 > /* > --=20 > 2.25.1 >=20 >=20