From nobody Fri Dec 19 07:16:39 2025 Received: from us-smtp-delivery-124.mimecast.com (us-smtp-delivery-124.mimecast.com [170.10.129.124]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 16C9385260 for ; Wed, 19 Feb 2025 02:18:20 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=170.10.129.124 ARC-Seal: i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1739931503; cv=none; b=biUT5iFUoRNHUlItqEVvWzwf9waXtCUHdjz3MP37I1tZ2KVsv6yKrwu5FQtM6bV9UGm6D1TCAOvsOcx+iORJXJ+uieqOqdGbU5Mbj5LB0XwoV1V8UP1i/z3kK3dWDmoFcJVOpFNtbxr0wpAd5/BFZQM1rqzgTJaoAoSoI2eBuBg= ARC-Message-Signature: i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1739931503; c=relaxed/simple; bh=qPogO3+SURGDVctjzFSU9aTDFySdl7GETz8GHCW3wlk=; h=From:To:Cc:Subject:Date:Message-ID:In-Reply-To:References: MIME-Version; b=PX5aDd8ZXzQGxrrYoBfELhrHjFqSpg1Zou4ECZ1MxMDyAfyt8QGuqQo6LPwYhSkXBNAw67zjvVVOzS8FvOqkM8d7zw4B+nO8h26p8Zo3+DgLtJ2dlAT24GAhAIObWu2j21F545xyHs+r0S+bfWo2k+m2S+G3eaH18cNumYXv9y4= ARC-Authentication-Results: i=1; smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=redhat.com; spf=pass smtp.mailfrom=redhat.com; dkim=pass (1024-bit key) header.d=redhat.com header.i=@redhat.com header.b=AxmZOGZs; arc=none smtp.client-ip=170.10.129.124 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=redhat.com Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=redhat.com Authentication-Results: smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=redhat.com header.i=@redhat.com header.b="AxmZOGZs" DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1739931500; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references; bh=GvFM6GZiRQiXqBZ3vCZFiH0Ays3za6p0+8us7Xm2FsA=; b=AxmZOGZs2dhHxNycOG02YO2p/7RouMIIc2z4m20K2KX0aDn7B1fjcX67jB5MuolJo4n0HG Vwfp1cFjA9ZEfJ6yD2oNehoM/5UxmrBazDADXkOQEVh/IT8W1nxg0Gie1V82JDmGIPByZe mx/YjGRqtrvvPXsmcGDGn12OQBxGWU4= Received: from mx-prod-mc-08.mail-002.prod.us-west-2.aws.redhat.com (ec2-35-165-154-97.us-west-2.compute.amazonaws.com [35.165.154.97]) by relay.mimecast.com with ESMTP with STARTTLS (version=TLSv1.3, cipher=TLS_AES_256_GCM_SHA384) id us-mta-633-uF3_mlKrM2imXHAX3cLYTQ-1; Tue, 18 Feb 2025 21:18:16 -0500 X-MC-Unique: uF3_mlKrM2imXHAX3cLYTQ-1 X-Mimecast-MFC-AGG-ID: uF3_mlKrM2imXHAX3cLYTQ_1739931495 Received: from mx-prod-int-02.mail-002.prod.us-west-2.aws.redhat.com (mx-prod-int-02.mail-002.prod.us-west-2.aws.redhat.com [10.30.177.15]) (using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256/256 bits) key-exchange X25519 server-signature RSA-PSS (2048 bits) server-digest SHA256) (No client certificate requested) by mx-prod-mc-08.mail-002.prod.us-west-2.aws.redhat.com (Postfix) with ESMTPS id 13B48180087A; Wed, 19 Feb 2025 02:18:15 +0000 (UTC) Received: from fedora.redhat.com (unknown [10.22.65.50]) by mx-prod-int-02.mail-002.prod.us-west-2.aws.redhat.com (Postfix) with ESMTP id BC6A719560B9; Wed, 19 Feb 2025 02:18:12 +0000 (UTC) From: Luiz Capitulino To: linux-kernel@vger.kernel.org, linux-mm@kvack.org, david@redhat.com, yuzhao@google.com, pasha.tatashin@soleen.com Cc: akpm@linux-foundation.org, hannes@cmpxchg.org, muchun.song@linux.dev, luizcap@redhat.com Subject: [PATCH 1/4] mm: page_ext: add an iteration API for page extensions Date: Tue, 18 Feb 2025 21:17:47 -0500 Message-ID: <3f0e058aef3951b39cf6bb4259c247352d4fe736.1739931468.git.luizcap@redhat.com> In-Reply-To: References: Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: quoted-printable X-Scanned-By: MIMEDefang 3.0 on 10.30.177.15 Content-Type: text/plain; charset="utf-8" The page extension implementation assumes that all page extensions of a given page order are stored in the same memory section. The function page_ext_next() relies on this assumption by adding an offset to the current object to return the next adjacent page extension. This behavior works as expected for flatmem but fails for sparsemem when using 1G pages. The commit cf54f310d0d3 ("mm/hugetlb: use __GFP_COMP for gigantic folios") exposes this issue, making it possible for a crash when using page_owner or page_table_check page extensions. The problem is that for 1G pages, the page extensions may span memory section boundaries and be stored in different memory sections. This issue was not visible before commit cf54f310d0d3 ("mm/hugetlb: use __GFP_COMP for gigantic folios") because alloc_contig_pages() never passed more than MAX_PAGE_ORDER to post_alloc_hook(). However, the series introducing mentioned commit changed this behavior allowing the full 1G page order to be passed. Reproducer: 1. Build the kernel with CONFIG_SPARSEMEM=3Dy and table extensions support 2. Pass 'default_hugepagesz=3D1 page_owner=3Don' in the kernel command-line 3. Reserve one 1G page at run-time, this should crash (backtrace below) To address this issue, this commit introduces a new API for iterating through page extensions. The main iteration loops are for_each_page_ext() and for_each_page_ext_order(). Both must be called with the RCU read lock taken. Here's an usage example: """ struct page_ext_iter iter; struct page_ext *page_ext; ... rcu_read_lock(); for_each_page_ext_order(page, order, page_ext, iter) { struct my_page_ext *obj =3D get_my_page_ext_obj(page_ext); ... } rcu_read_unlock(); """ Both loop constructs use page_ext_iter_next(), which checks to see if we have crossed sections in the iteration. In this case, page_ext_iter_next() retrieves the next page_ext object from another section. Thanks to David Hildenbrand for helping identify the root cause and providing suggestions on how to fix and optmize the solution (final implementation and bugs are all mine through). Lastly, here's the backtrace, without kasan you can get random crashes: [ 76.052526] BUG: KASAN: slab-out-of-bounds in __update_page_owner_handle= +0x238/0x298 [ 76.060283] Write of size 4 at addr ffff07ff96240038 by task tee/3598 [ 76.066714] [ 76.068203] CPU: 88 UID: 0 PID: 3598 Comm: tee Kdump: loaded Not tainted= 6.13.0-rep1 #3 [ 76.076202] Hardware name: WIWYNN Mt.Jade Server System B81.030Z1.0007/M= t.Jade Motherboard, BIOS 2.10.20220810 (SCP: 2.10.20220810) 2022/08/10 [ 76.088972] Call trace: [ 76.091411] show_stack+0x20/0x38 (C) [ 76.095073] dump_stack_lvl+0x80/0xf8 [ 76.098733] print_address_description.constprop.0+0x88/0x398 [ 76.104476] print_report+0xa8/0x278 [ 76.108041] kasan_report+0xa8/0xf8 [ 76.111520] __asan_report_store4_noabort+0x20/0x30 [ 76.116391] __update_page_owner_handle+0x238/0x298 [ 76.121259] __set_page_owner+0xdc/0x140 [ 76.125173] post_alloc_hook+0x190/0x1d8 [ 76.129090] alloc_contig_range_noprof+0x54c/0x890 [ 76.133874] alloc_contig_pages_noprof+0x35c/0x4a8 [ 76.138656] alloc_gigantic_folio.isra.0+0x2c0/0x368 [ 76.143616] only_alloc_fresh_hugetlb_folio.isra.0+0x24/0x150 [ 76.149353] alloc_pool_huge_folio+0x11c/0x1f8 [ 76.153787] set_max_huge_pages+0x364/0xca8 [ 76.157961] __nr_hugepages_store_common+0xb0/0x1a0 [ 76.162829] nr_hugepages_store+0x108/0x118 [ 76.167003] kobj_attr_store+0x3c/0x70 [ 76.170745] sysfs_kf_write+0xfc/0x188 [ 76.174492] kernfs_fop_write_iter+0x274/0x3e0 [ 76.178927] vfs_write+0x64c/0x8e0 [ 76.182323] ksys_write+0xf8/0x1f0 [ 76.185716] __arm64_sys_write+0x74/0xb0 [ 76.189630] invoke_syscall.constprop.0+0xd8/0x1e0 [ 76.194412] do_el0_svc+0x164/0x1e0 [ 76.197891] el0_svc+0x40/0xe0 [ 76.200939] el0t_64_sync_handler+0x144/0x168 [ 76.205287] el0t_64_sync+0x1ac/0x1b0 Fixes: cf54f310d0d3 ("mm/hugetlb: use __GFP_COMP for gigantic folios") Signed-off-by: Luiz Capitulino --- include/linux/page_ext.h | 66 ++++++++++++++++++++++++++++++++++++++++ mm/page_ext.c | 41 +++++++++++++++++++++++++ 2 files changed, 107 insertions(+) diff --git a/include/linux/page_ext.h b/include/linux/page_ext.h index e4b48a0dda244..a99da12e59fa7 100644 --- a/include/linux/page_ext.h +++ b/include/linux/page_ext.h @@ -3,6 +3,7 @@ #define __LINUX_PAGE_EXT_H =20 #include +#include #include =20 struct pglist_data; @@ -69,12 +70,26 @@ extern void page_ext_init(void); static inline void page_ext_init_flatmem_late(void) { } + +static inline bool page_ext_iter_next_fast_possible(unsigned long next_pfn) +{ + /* + * page_ext is allocated per memory section. Once we cross a + * memory section, we have to fetch the new pointer. + */ + return next_pfn % PAGES_PER_SECTION; +} #else extern void page_ext_init_flatmem(void); extern void page_ext_init_flatmem_late(void); static inline void page_ext_init(void) { } + +static inline bool page_ext_iter_next_fast_possible(unsigned long next_pfn) +{ + return true; +} #endif =20 extern struct page_ext *page_ext_get(const struct page *page); @@ -93,6 +108,57 @@ static inline struct page_ext *page_ext_next(struct pag= e_ext *curr) return next; } =20 +struct page_ext_iter { + unsigned long pfn; + unsigned long index; + struct page_ext *page_ext; +}; + +struct page_ext *page_ext_iter_begin(struct page_ext_iter *iter, struct pa= ge *page); +struct page_ext *page_ext_iter_next(struct page_ext_iter *iter); + +/** + * page_ext_iter_get() - Get current page extension + * @iter: page extension iterator. + * + * Return: NULL if no page_ext exists for this iterator. + */ +static inline struct page_ext *page_ext_iter_get(const struct page_ext_ite= r *iter) +{ + return iter->page_ext; +} + +/** + * for_each_page_ext(): iterate through page_ext objects. + * @__page: the page we're interested in + * @__pgcount: how many pages to iterate through + * @__page_ext: struct page_ext pointer where the current page_ext + * object is returned + * @__iter: struct page_ext_iter object (defined in the stack) + * + * IMPORTANT: must be called with RCU read lock taken. + */ +#define for_each_page_ext(__page, __pgcount, __page_ext, __iter) \ + __page_ext =3D page_ext_iter_begin(&__iter, __page); \ + for (__iter.index =3D 0; \ + __page_ext && __iter.index < __pgcount; \ + __page_ext =3D page_ext_iter_next(&__iter), \ + __iter.index++) + +/** + * for_each_page_ext_order(): iterate through page_ext objects + * for a given page order + * @__page: the page we're interested in + * @__order: page order to iterate through + * @__page_ext: struct page_ext pointer where the current page_ext + * object is returned + * @__iter: struct page_ext_iter object (defined in the stack) + * + * IMPORTANT: must be called with RCU read lock taken. + */ +#define for_each_page_ext_order(__page, __order, __page_ext, __iter) \ + for_each_page_ext(__page, (1UL << __order), __page_ext, __iter) + #else /* !CONFIG_PAGE_EXTENSION */ struct page_ext; =20 diff --git a/mm/page_ext.c b/mm/page_ext.c index 641d93f6af4c1..508deb04d5ead 100644 --- a/mm/page_ext.c +++ b/mm/page_ext.c @@ -549,3 +549,44 @@ void page_ext_put(struct page_ext *page_ext) =20 rcu_read_unlock(); } + +/** + * page_ext_iter_begin() - Prepare for iterating through page extensions. + * @iter: page extension iterator. + * @page: The page we're interested in. + * + * Must be called with RCU read lock taken. + * + * Return: NULL if no page_ext exists for this page. + */ +struct page_ext *page_ext_iter_begin(struct page_ext_iter *iter, struct pa= ge *page) +{ + iter->pfn =3D page_to_pfn(page); + iter->page_ext =3D lookup_page_ext(page); + + return iter->page_ext; +} + +/** + * page_ext_iter_next() - Get next page extension + * @iter: page extension iterator. + * + * Must be called with RCU read lock taken. + * + * Return: NULL if no next page_ext exists. + */ +struct page_ext *page_ext_iter_next(struct page_ext_iter *iter) +{ + if (WARN_ON_ONCE(!iter->page_ext)) + return NULL; + + iter->pfn++; + + if (page_ext_iter_next_fast_possible(iter->pfn)) { + iter->page_ext =3D page_ext_next(iter->page_ext); + } else { + iter->page_ext =3D lookup_page_ext(pfn_to_page(iter->pfn)); + } + + return iter->page_ext; +} --=20 2.48.1