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[2620:137:e000::1:20]) by mx.google.com with ESMTP id v17-20020a056a00149100b005615ef4cfccsi4241744pfu.185.2022.12.16.17.56.08; Fri, 16 Dec 2022 17:56:20 -0800 (PST) Received-SPF: pass (google.com: domain of linux-kernel-owner@vger.kernel.org designates 2620:137:e000::1:20 as permitted sender) client-ip=2620:137:e000::1:20; Authentication-Results: mx.google.com; dkim=pass header.i=@redhat.com header.s=mimecast20190719 header.b=fiZzwKbK; spf=pass (google.com: domain of linux-kernel-owner@vger.kernel.org designates 2620:137:e000::1:20 as permitted sender) smtp.mailfrom=linux-kernel-owner@vger.kernel.org; dmarc=pass (p=NONE sp=NONE dis=NONE) header.from=redhat.com Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S229964AbiLQBzm (ORCPT <rfc822;jeantsuru.cumc.mandola@gmail.com> + 99 others); Fri, 16 Dec 2022 20:55:42 -0500 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:33842 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S229469AbiLQBzg (ORCPT <rfc822;linux-kernel@vger.kernel.org>); Fri, 16 Dec 2022 20:55:36 -0500 Received: from us-smtp-delivery-124.mimecast.com (us-smtp-delivery-124.mimecast.com [170.10.133.124]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 11E5E442F3 for <linux-kernel@vger.kernel.org>; Fri, 16 Dec 2022 17:54:47 -0800 (PST) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1671242087; 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; bh=KlAUk4Rvv2uJ6My8k7MBoYVwmIEIsjetFKSoMLOi3Uk=; b=fiZzwKbK7SH0qWwTwKC+fPVo+GiM1+3GBW3RCQd9/oP9DwwLZ2ctbDTr2g4GATzx3y1z5T YHOIiIU9LulyaOP21FToPpTK0a6qUS5GDXBGxGyuv/HHKjHh3zeG4oa/brKVcew19HQe/l LyFziE3uk0akXSXmmARf9k704TDiOSk= Received: from mimecast-mx02.redhat.com (mimecast-mx02.redhat.com [66.187.233.88]) by relay.mimecast.com with ESMTP with STARTTLS (version=TLSv1.2, cipher=TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384) id us-mta-422-Y2byrGHOOMmErGkLv8UWzQ-1; Fri, 16 Dec 2022 20:54:43 -0500 X-MC-Unique: Y2byrGHOOMmErGkLv8UWzQ-1 Received: from smtp.corp.redhat.com (int-mx10.intmail.prod.int.rdu2.redhat.com [10.11.54.10]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mimecast-mx02.redhat.com (Postfix) with ESMTPS id 63378802C1C; Sat, 17 Dec 2022 01:54:43 +0000 (UTC) Received: from MiWiFi-R3L-srv.redhat.com (ovpn-12-34.pek2.redhat.com [10.72.12.34]) by smtp.corp.redhat.com (Postfix) with ESMTP id 572DA400F5B; Sat, 17 Dec 2022 01:54:38 +0000 (UTC) From: Baoquan He <bhe@redhat.com> To: linux-kernel@vger.kernel.org Cc: linux-mm@kvack.org, urezki@gmail.com, stephen.s.brennan@oracle.com, willy@infradead.org, akpm@linux-foundation.org, hch@infradead.org, Baoquan He <bhe@redhat.com> Subject: [PATCH v2 0/7] mm/vmalloc.c: allow vread() to read out vm_map_ram areas Date: Sat, 17 Dec 2022 09:54:28 +0800 Message-Id: <20221217015435.73889-1-bhe@redhat.com> MIME-Version: 1.0 Content-type: text/plain Content-Transfer-Encoding: 8bit X-Scanned-By: MIMEDefang 3.1 on 10.11.54.10 X-Spam-Status: No, score=-2.1 required=5.0 tests=BAYES_00,DKIMWL_WL_HIGH, DKIM_SIGNED,DKIM_VALID,DKIM_VALID_AU,DKIM_VALID_EF,RCVD_IN_DNSWL_NONE, RCVD_IN_MSPIKE_H2,SPF_HELO_NONE,SPF_NONE autolearn=ham autolearn_force=no version=3.4.6 X-Spam-Checker-Version: SpamAssassin 3.4.6 (2021-04-09) on lindbergh.monkeyblade.net Precedence: bulk List-ID: <linux-kernel.vger.kernel.org> X-Mailing-List: linux-kernel@vger.kernel.org X-getmail-retrieved-from-mailbox: =?utf-8?q?INBOX?= X-GMAIL-THRID: =?utf-8?q?1751245207010757996?= X-GMAIL-MSGID: =?utf-8?q?1752424440919462071?= |
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mm/vmalloc.c: allow vread() to read out vm_map_ram areas
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Message
Baoquan He
Dec. 17, 2022, 1:54 a.m. UTC
Problem: *** Stephen reported vread() will skip vm_map_ram areas when reading out /proc/kcore with drgn utility. Please see below link to get more about it: /proc/kcore reads 0's for vmap_block https://lore.kernel.org/all/87ilk6gos2.fsf@oracle.com/T/#u Root cause: *** The normal vmalloc API uses struct vmap_area to manage the virtual kernel area allocated and associate a vm_struct to store more information and passed out. However, area reserved through vm_map_ram() interface doesn't allocate vm_struct to bind with. So the current code in vread() will skip the vm_map_ram area through 'if (!va->vm)' conditional checking. Solution: *** There are two types of vm_map_ram area. One is the whole vmap_area being reserved and mapped at one time; the other is the whole vmap_area with VMAP_BLOCK_SIZE size being reserved at one time, while mapped into split regions with smaller size several times via vb_alloc(). I will call the 2nd type vb region. In patch 1 and 2, add flags into struct vmap_area to mark these two types of vm_map_ram area, meanwhile add bitmap field used_map into struct vmap_block to mark those vb regions being used to differentiate with dirty and free regions in vmap_block. With the help of above vmap_area->flags and vmap_block->used_map, we can recognize them in vread() and handle them respectively in patch 3. Besides, *** In patch 5, let's ignore vmap area with VM_UNINITIALIZED set in vm->flags, because this kind of area is created by calling __vmalloc_node_range(), VM_UNINITIALIZED set indicating it has vm_struct associated with, but is still during the page allocating and mapping process. In patch 6 and 7, change area flag from VM_ALLOC to VM_IOREMAP in two places. This will show them as 'ioremap' in /proc/vmallocinfo, and exclude them from /proc/kcore. Testing *** Only did the basic testing. Changelog *** v1->v2: - Change alloc_vmap_area() to pass in va_flags so that we can pass and set vmap_area->flags for vm_map_ram area. With this, no extra action need be added to acquire vmap_area_lock when doing the vmap_area->flags setting. Uladzislau reviewed v1 and pointed out the issue. - Improve vb_vread() to cover the case where reading is started from a dirty or free region. RFC->v1: - Add a new field flags in vmap_area to mark vm_map_ram area. It cold be risky reusing the vm union in vmap_area in RFC. I will consider reusing the union in vmap_area to save memory later. Now just take the simpler way to let's focus on resolving the main problem. - Add patch 4~7 for optimization. Baoquan He (7): mm/vmalloc.c: add used_map into vmap_block to track space of vmap_block mm/vmalloc.c: add flags to mark vm_map_ram area mm/vmalloc.c: allow vread() to read out vm_map_ram areas mm/vmalloc: explicitly identify vm_map_ram area when shown in /proc/vmcoreinfo mm/vmalloc: skip the uninitilized vmalloc areas powerpc: mm: add VM_IOREMAP flag to the vmalloc area sh: mm: set VM_IOREMAP flag to the vmalloc area arch/powerpc/kernel/pci_64.c | 2 +- arch/sh/kernel/cpu/sh4/sq.c | 2 +- include/linux/vmalloc.h | 1 + mm/vmalloc.c | 106 +++++++++++++++++++++++++++++------ 4 files changed, 92 insertions(+), 19 deletions(-)