From nobody Mon May 11 06:18:53 2026 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 B31E7C433EF for ; Tue, 12 Apr 2022 20:27:59 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S230108AbiDLU3u (ORCPT ); Tue, 12 Apr 2022 16:29:50 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:48992 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S230092AbiDLU25 (ORCPT ); Tue, 12 Apr 2022 16:28:57 -0400 Received: from alexa-out-sd-02.qualcomm.com (alexa-out-sd-02.qualcomm.com [199.106.114.39]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 398BEA27FE for ; Tue, 12 Apr 2022 13:26:38 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=quicinc.com; i=@quicinc.com; q=dns/txt; s=qcdkim; t=1649795198; x=1681331198; h=from:to:cc:subject:date:message-id; bh=U07zXEF5XKiHrZJWluQBPtBzbqwPfha91C4VetzKe+k=; b=MPnKibYpukiTeiB26W9N+TTrKBB6SQvdgM4+UatuPVtjGBFgHLsrPvL1 Bk25ICjv+CH91oM6zO5bG4o7/NVpEKi1E0B4mXgdOI1DiUwRj0wkZFeBD 02OS564KT8q7HH2ePzoCMKYs8E8DkQhnEYYj7UJn/0eN4+KTHTXx6Zsvq I=; Received: from unknown (HELO ironmsg-SD-alpha.qualcomm.com) ([10.53.140.30]) by alexa-out-sd-02.qualcomm.com with ESMTP; 12 Apr 2022 13:17:03 -0700 X-QCInternal: smtphost Received: from th-lint-014.qualcomm.com ([10.63.177.51]) by ironmsg-SD-alpha.qualcomm.com with ESMTP; 12 Apr 2022 13:17:02 -0700 Received: by th-lint-014.qualcomm.com (Postfix, from userid 455663) id DEC2B139C; Tue, 12 Apr 2022 13:17:02 -0700 (PDT) From: Sudarshan Rajagopalan To: Andrew Morton , linux-mm@kvack.org, linux-kernel@vger.kernel.org Cc: Sudarshan Rajagopalan , Mike Rapoport , Anshuman Khandual , Suren Baghdasaryan Subject: [PATCH] mm, page_alloc: check pfn is valid before moving to freelist Date: Tue, 12 Apr 2022 13:16:23 -0700 Message-Id: X-Mailer: git-send-email 2.7.4 In-Reply-To: References: In-Reply-To: References: Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Transfer-Encoding: quoted-printable MIME-Version: 1.0 Content-Type: text/plain; charset="utf-8" Check if pfn is valid before or not before moving it to freelist. There are possible scenario where a pageblock can have partial physical hole and partial part of System RAM. This happens when base address in RAM partition table is not aligned to pageblock size. Example: Say we have this first two entries in RAM partition table - Base Addr: 0x0000000080000000 Length: 0x0000000058000000 Base Addr: 0x00000000E3930000 Length: 0x0000000020000000 ... Physical hole: 0xD8000000 - 0xE3930000 On system having 4K as page size and hence pageblock size being 4MB, the base address 0xE3930000 is not aligned to 4MB pageblock size. Now we will have pageblock which has partial physical hole and partial part of System RAM - Pageblock [0xE3800000 - 0xE3C00000] - 0xE3800000 - 0xE3930000 -- physical hole 0xE3930000 - 0xE3C00000 -- System RAM Now doing __alloc_pages say we get a valid page with PFN 0xE3B00 from __rmqueue_fallback, we try to put other pages from the same pageblock as we= ll into freelist by calling steal_suitable_fallback(). We then search for freepages from start of the pageblock due to below code - move_freepages_block(zone, page, migratetype, ...) { pfn =3D page_to_pfn(page); start_pfn =3D pfn & ~(pageblock_nr_pages - 1); end_pfn =3D start_pfn + pageblock_nr_pages - 1; ... } With the pageblock which has partial physical hole at the beginning, we will run into PFNs from the physical hole whose struct page is not initialized a= nd is invalid, and system would crash as we operate on invalid struct page to = find out of page is in Buddy or LRU or not [ 107.629453][ T9688] Unable to handle kernel NULL pointer dereference at = virtual address 0000000000000000 [ 107.639214][ T9688] Mem abort info: [ 107.642829][ T9688] ESR =3D 0x96000006 [ 107.646696][ T9688] EC =3D 0x25: DABT (current EL), IL =3D 32 bits [ 107.652878][ T9688] SET =3D 0, FnV =3D 0 [ 107.656751][ T9688] EA =3D 0, S1PTW =3D 0 [ 107.660705][ T9688] FSC =3D 0x06: level 2 translation fault [ 107.666455][ T9688] Data abort info: [ 107.670151][ T9688] ISV =3D 0, ISS =3D 0x00000006 [ 107.674827][ T9688] CM =3D 0, WnR =3D 0 [ 107.678615][ T9688] user pgtable: 4k pages, 39-bit VAs, pgdp=3D000000098= a237000 [ 107.685970][ T9688] [0000000000000000] pgd=3D0800000987170003, p4d=3D080= 0000987170003, pud=3D0800000987170003, pmd=3D0000000000000000 [ 107.697582][ T9688] Internal error: Oops: 96000006 [#1] PREEMPT SMP [ 108.209839][ T9688] pc : move_freepages_block+0x174/0x27c [ 108.215407][ T9688] lr : steal_suitable_fallback+0x20c/0x398 [ 108.305908][ T9688] Call trace: [ 108.309151][ T9688] move_freepages_block+0x174/0x27c [PageLRU] [ 108.314359][ T9688] steal_suitable_fallback+0x20c/0x398 [ 108.319826][ T9688] rmqueue_bulk+0x250/0x934 [ 108.324325][ T9688] rmqueue_pcplist+0x178/0x2ac [ 108.329086][ T9688] rmqueue+0x5c/0xc10 [ 108.333048][ T9688] get_page_from_freelist+0x19c/0x430 [ 108.338430][ T9688] __alloc_pages+0x134/0x424 [ 108.343017][ T9688] page_cache_ra_unbounded+0x120/0x324 [ 108.348494][ T9688] do_sync_mmap_readahead+0x1b0/0x234 [ 108.353878][ T9688] filemap_fault+0xe0/0x4c8 [ 108.358375][ T9688] do_fault+0x168/0x6cc [ 108.362518][ T9688] handle_mm_fault+0x5c4/0x848 [ 108.367280][ T9688] do_page_fault+0x3fc/0x5d0 [ 108.371867][ T9688] do_translation_fault+0x6c/0x1b0 [ 108.376985][ T9688] do_mem_abort+0x68/0x10c [ 108.381389][ T9688] el0_ia+0x50/0xbc [ 108.385175][ T9688] el0t_32_sync_handler+0x88/0xbc [ 108.390208][ T9688] el0t_32_sync+0x1b8/0x1bc Hence, avoid operating on invalid pages within the same pageblock by checki= ng if pfn is valid or not. Signed-off-by: Sudarshan Rajagopalan Fixes: 4c7b9896621be ("mm: remove pfn_valid_within() and CONFIG_HOLES_IN_ZO= NE") Cc: Mike Rapoport Cc: Anshuman Khandual Cc: Suren Baghdasaryan Acked-by: David Rientjes --- mm/page_alloc.c | 5 +++++ 1 file changed, 5 insertions(+) diff --git a/mm/page_alloc.c b/mm/page_alloc.c index 6e5b448..e87aa053 100644 --- a/mm/page_alloc.c +++ b/mm/page_alloc.c @@ -2521,6 +2521,11 @@ static int move_freepages(struct zone *zone, int pages_moved =3D 0; =20 for (pfn =3D start_pfn; pfn <=3D end_pfn;) { + if (!pfn_valid(pfn)) { + pfn++; + continue; + } + page =3D pfn_to_page(pfn); if (!PageBuddy(page)) { /* --=20 2.7.4