From nobody Wed Sep 3 01:42:14 2025 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 2DB56ECAAD5 for ; Fri, 2 Sep 2022 12:36:20 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S236856AbiIBMgS (ORCPT ); Fri, 2 Sep 2022 08:36:18 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:46674 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S236897AbiIBMe7 (ORCPT ); Fri, 2 Sep 2022 08:34:59 -0400 Received: from dfw.source.kernel.org (dfw.source.kernel.org [IPv6:2604:1380:4641:c500::1]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 19E63DDA9D; Fri, 2 Sep 2022 05:28:26 -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 dfw.source.kernel.org (Postfix) with ESMTPS id 4714262169; Fri, 2 Sep 2022 12:26:45 +0000 (UTC) Received: by smtp.kernel.org (Postfix) with ESMTPSA id 227A5C433C1; Fri, 2 Sep 2022 12:26:44 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=linuxfoundation.org; s=korg; t=1662121604; bh=fR9sprY+XFhzju+GknKGQWVKeO5tDoaSoCfhx3r0z8U=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=mo8TKiymtqD0rUNMi9oV2g/amlSlFBQzopyutxudK8aG4Jp9j+DrY6/ah700ACbwS StSIj2d2lL3XRRLTNV4fsfe5qBnMnwExuw6zQY6TrXjhThUPgFxiyaRBAukabQJOMt xuFh7rBNjVXS41gv5iPI9YGQbzZEbNeiSkP7wP7M= From: Greg Kroah-Hartman To: linux-kernel@vger.kernel.org Cc: Greg Kroah-Hartman , stable@vger.kernel.org, David Hildenbrand , Mike Kravetz , Peter Feiner , "Kirill A. Shutemov" , Cyrill Gorcunov , Pavel Emelyanov , Jamie Liu , Hugh Dickins , Naoya Horiguchi , Bjorn Helgaas , Muchun Song , Peter Xu , Andrew Morton Subject: [PATCH 4.19 34/56] mm/hugetlb: fix hugetlb not supporting softdirty tracking Date: Fri, 2 Sep 2022 14:18:54 +0200 Message-Id: <20220902121401.463956465@linuxfoundation.org> X-Mailer: git-send-email 2.37.3 In-Reply-To: <20220902121400.219861128@linuxfoundation.org> References: <20220902121400.219861128@linuxfoundation.org> User-Agent: quilt/0.67 MIME-Version: 1.0 Content-Transfer-Encoding: quoted-printable Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Type: text/plain; charset="utf-8" From: David Hildenbrand commit f96f7a40874d7c746680c0b9f57cef2262ae551f upstream. Patch series "mm/hugetlb: fix write-fault handling for shared mappings", v2. I observed that hugetlb does not support/expect write-faults in shared mappings that would have to map the R/O-mapped page writable -- and I found two case where we could currently get such faults and would erroneously map an anon page into a shared mapping. Reproducers part of the patches. I propose to backport both fixes to stable trees. The first fix needs a small adjustment. This patch (of 2): Staring at hugetlb_wp(), one might wonder where all the logic for shared mappings is when stumbling over a write-protected page in a shared mapping. In fact, there is none, and so far we thought we could get away with that because e.g., mprotect() should always do the right thing and map all pages directly writable. Looks like we were wrong: Reviewed-by: Mike Kravetz -------------------------------------------------------------------------- #include #include #include #include #include #include #include #define HUGETLB_SIZE (2 * 1024 * 1024u) static void clear_softdirty(void) { int fd =3D open("/proc/self/clear_refs", O_WRONLY); const char *ctrl =3D "4"; int ret; if (fd < 0) { fprintf(stderr, "open(clear_refs) failed\n"); exit(1); } ret =3D write(fd, ctrl, strlen(ctrl)); if (ret !=3D strlen(ctrl)) { fprintf(stderr, "write(clear_refs) failed\n"); exit(1); } close(fd); } int main(int argc, char **argv) { char *map; int fd; fd =3D open("/dev/hugepages/tmp", O_RDWR | O_CREAT); if (!fd) { fprintf(stderr, "open() failed\n"); return -errno; } if (ftruncate(fd, HUGETLB_SIZE)) { fprintf(stderr, "ftruncate() failed\n"); return -errno; } map =3D mmap(NULL, HUGETLB_SIZE, PROT_READ|PROT_WRITE, MAP_SHARED,= fd, 0); if (map =3D=3D MAP_FAILED) { fprintf(stderr, "mmap() failed\n"); return -errno; } *map =3D 0; if (mprotect(map, HUGETLB_SIZE, PROT_READ)) { fprintf(stderr, "mmprotect() failed\n"); return -errno; } clear_softdirty(); if (mprotect(map, HUGETLB_SIZE, PROT_READ|PROT_WRITE)) { fprintf(stderr, "mmprotect() failed\n"); return -errno; } *map =3D 0; return 0; } -------------------------------------------------------------------------- Above test fails with SIGBUS when there is only a single free hugetlb page. # echo 1 > /sys/kernel/mm/hugepages/hugepages-2048kB/nr_hugepages # ./test Bus error (core dumped) And worse, with sufficient free hugetlb pages it will map an anonymous page into a shared mapping, for example, messing up accounting during unmap and breaking MAP_SHARED semantics: # echo 2 > /sys/kernel/mm/hugepages/hugepages-2048kB/nr_hugepages # ./test # cat /proc/meminfo | grep HugePages_ HugePages_Total: 2 HugePages_Free: 1 HugePages_Rsvd: 18446744073709551615 HugePages_Surp: 0 Reason in this particular case is that vma_wants_writenotify() will return "true", removing VM_SHARED in vma_set_page_prot() to map pages write-protected. Let's teach vma_wants_writenotify() that hugetlb does not support softdirty tracking. Link: https://lkml.kernel.org/r/20220811103435.188481-1-david@redhat.com Link: https://lkml.kernel.org/r/20220811103435.188481-2-david@redhat.com Fixes: 64e455079e1b ("mm: softdirty: enable write notifications on VMAs aft= er VM_SOFTDIRTY cleared") Signed-off-by: David Hildenbrand Reviewed-by: Mike Kravetz Cc: Peter Feiner Cc: Kirill A. Shutemov Cc: Cyrill Gorcunov Cc: Pavel Emelyanov Cc: Jamie Liu Cc: Hugh Dickins Cc: Naoya Horiguchi Cc: Bjorn Helgaas Cc: Muchun Song Cc: Peter Xu Cc: [3.18+] Signed-off-by: Andrew Morton Signed-off-by: David Hildenbrand Signed-off-by: Greg Kroah-Hartman --- mm/mmap.c | 8 ++++++-- 1 file changed, 6 insertions(+), 2 deletions(-) --- a/mm/mmap.c +++ b/mm/mmap.c @@ -1640,8 +1640,12 @@ int vma_wants_writenotify(struct vm_area pgprot_val(vm_pgprot_modify(vm_page_prot, vm_flags))) return 0; =20 - /* Do we need to track softdirty? */ - if (IS_ENABLED(CONFIG_MEM_SOFT_DIRTY) && !(vm_flags & VM_SOFTDIRTY)) + /* + * Do we need to track softdirty? hugetlb does not support softdirty + * tracking yet. + */ + if (IS_ENABLED(CONFIG_MEM_SOFT_DIRTY) && !(vm_flags & VM_SOFTDIRTY) && + !is_vm_hugetlb_page(vma)) return 1; =20 /* Specialty mapping? */