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 X-Spam-Level: X-Spam-Status: No, score=-12.4 required=3.0 tests=BAYES_00,DKIMWL_WL_HIGH, DKIM_SIGNED,DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS, INCLUDES_PATCH,MAILING_LIST_MULTI,NICE_REPLY_A,SIGNED_OFF_BY,SPF_HELO_NONE, SPF_PASS,USER_AGENT_SANE_1 autolearn=ham autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id CDF93C433E7 for ; Thu, 15 Oct 2020 08:50:40 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 6F655218AC for ; Thu, 15 Oct 2020 08:50:40 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (1024-bit key) header.d=redhat.com header.i=@redhat.com header.b="JHjpYuBT" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1730423AbgJOIuj (ORCPT ); Thu, 15 Oct 2020 04:50:39 -0400 Received: from us-smtp-delivery-124.mimecast.com ([216.205.24.124]:46869 "EHLO us-smtp-delivery-124.mimecast.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726329AbgJOIui (ORCPT ); Thu, 15 Oct 2020 04:50:38 -0400 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1602751836; 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:autocrypt:autocrypt; bh=8g0dEJ4HjLmnMAQQi1r5OiIA7ugQGWhb4UgQjxmr0MY=; b=JHjpYuBTAZBVKoSFNkcKgXR1/pSnT8/XQvAjfx4/tfP15f+2dniJxlh1hHdmH8PsgS8+3I Sg010DfxS4uQSdv2mtZDniqovswKOupd+5Ctd7VxWXxD0JNoN7ERj3P9w9mYDNDPU7WyOQ ciGXGC1r6CChWdfxM8nYfuVLIclFv7A= Received: from mimecast-mx01.redhat.com (mimecast-mx01.redhat.com [209.132.183.4]) (Using TLS) by relay.mimecast.com with ESMTP id us-mta-457-QmxSiLYUMiaS3T7c_0bKaw-1; Thu, 15 Oct 2020 04:50:34 -0400 X-MC-Unique: QmxSiLYUMiaS3T7c_0bKaw-1 Received: from smtp.corp.redhat.com (int-mx07.intmail.prod.int.phx2.redhat.com [10.5.11.22]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mimecast-mx01.redhat.com (Postfix) with ESMTPS id 990B0190A3E4; Thu, 15 Oct 2020 08:50:32 +0000 (UTC) Received: from [10.36.114.207] (ovpn-114-207.ams2.redhat.com [10.36.114.207]) by smtp.corp.redhat.com (Postfix) with ESMTP id 0865A100238E; Thu, 15 Oct 2020 08:50:27 +0000 (UTC) Subject: Re: [PATCH v1 05/29] virtio-mem: generalize check for added memory To: Wei Yang Cc: linux-kernel@vger.kernel.org, linux-mm@kvack.org, virtualization@lists.linux-foundation.org, Andrew Morton , "Michael S . Tsirkin" , Jason Wang , Pankaj Gupta References: <20201012125323.17509-1-david@redhat.com> <20201012125323.17509-6-david@redhat.com> <20201015082808.GE86495@L-31X9LVDL-1304.local> From: David Hildenbrand Autocrypt: addr=david@redhat.com; prefer-encrypt=mutual; keydata= mQINBFXLn5EBEAC+zYvAFJxCBY9Tr1xZgcESmxVNI/0ffzE/ZQOiHJl6mGkmA1R7/uUpiCjJ dBrn+lhhOYjjNefFQou6478faXE6o2AhmebqT4KiQoUQFV4R7y1KMEKoSyy8hQaK1umALTdL QZLQMzNE74ap+GDK0wnacPQFpcG1AE9RMq3aeErY5tujekBS32jfC/7AnH7I0v1v1TbbK3Gp XNeiN4QroO+5qaSr0ID2sz5jtBLRb15RMre27E1ImpaIv2Jw8NJgW0k/D1RyKCwaTsgRdwuK Kx/Y91XuSBdz0uOyU/S8kM1+ag0wvsGlpBVxRR/xw/E8M7TEwuCZQArqqTCmkG6HGcXFT0V9 PXFNNgV5jXMQRwU0O/ztJIQqsE5LsUomE//bLwzj9IVsaQpKDqW6TAPjcdBDPLHvriq7kGjt WhVhdl0qEYB8lkBEU7V2Yb+SYhmhpDrti9Fq1EsmhiHSkxJcGREoMK/63r9WLZYI3+4W2rAc UucZa4OT27U5ZISjNg3Ev0rxU5UH2/pT4wJCfxwocmqaRr6UYmrtZmND89X0KigoFD/XSeVv jwBRNjPAubK9/k5NoRrYqztM9W6sJqrH8+UWZ1Idd/DdmogJh0gNC0+N42Za9yBRURfIdKSb B3JfpUqcWwE7vUaYrHG1nw54pLUoPG6sAA7Mehl3nd4pZUALHwARAQABtCREYXZpZCBIaWxk ZW5icmFuZCA8ZGF2aWRAcmVkaGF0LmNvbT6JAlgEEwEIAEICGwMGCwkIBwMCBhUIAgkKCwQW AgMBAh4BAheAAhkBFiEEG9nKrXNcTDpGDfzKTd4Q9wD/g1oFAl8Ox4kFCRKpKXgACgkQTd4Q 9wD/g1oHcA//a6Tj7SBNjFNM1iNhWUo1lxAja0lpSodSnB2g4FCZ4R61SBR4l/psBL73xktp rDHrx4aSpwkRP6Epu6mLvhlfjmkRG4OynJ5HG1gfv7RJJfnUdUM1z5kdS8JBrOhMJS2c/gPf wv1TGRq2XdMPnfY2o0CxRqpcLkx4vBODvJGl2mQyJF/gPepdDfcT8/PY9BJ7FL6Hrq1gnAo4 3Iv9qV0JiT2wmZciNyYQhmA1V6dyTRiQ4YAc31zOo2IM+xisPzeSHgw3ONY/XhYvfZ9r7W1l pNQdc2G+o4Di9NPFHQQhDw3YTRR1opJaTlRDzxYxzU6ZnUUBghxt9cwUWTpfCktkMZiPSDGd KgQBjnweV2jw9UOTxjb4LXqDjmSNkjDdQUOU69jGMUXgihvo4zhYcMX8F5gWdRtMR7DzW/YE BgVcyxNkMIXoY1aYj6npHYiNQesQlqjU6azjbH70/SXKM5tNRplgW8TNprMDuntdvV9wNkFs 9TyM02V5aWxFfI42+aivc4KEw69SE9KXwC7FSf5wXzuTot97N9Phj/Z3+jx443jo2NR34XgF 89cct7wJMjOF7bBefo0fPPZQuIma0Zym71cP61OP/i11ahNye6HGKfxGCOcs5wW9kRQEk8P9 M/k2wt3mt/fCQnuP/mWutNPt95w9wSsUyATLmtNrwccz63W5Ag0EVcufkQEQAOfX3n0g0fZz Bgm/S2zF/kxQKCEKP8ID+Vz8sy2GpDvveBq4H2Y34XWsT1zLJdvqPI4af4ZSMxuerWjXbVWb T6d4odQIG0fKx4F8NccDqbgHeZRNajXeeJ3R7gAzvWvQNLz4piHrO/B4tf8svmRBL0ZB5P5A 2uhdwLU3NZuK22zpNn4is87BPWF8HhY0L5fafgDMOqnf4guJVJPYNPhUFzXUbPqOKOkL8ojk CXxkOFHAbjstSK5Ca3fKquY3rdX3DNo+EL7FvAiw1mUtS+5GeYE+RMnDCsVFm/C7kY8c2d0G NWkB9pJM5+mnIoFNxy7YBcldYATVeOHoY4LyaUWNnAvFYWp08dHWfZo9WCiJMuTfgtH9tc75 7QanMVdPt6fDK8UUXIBLQ2TWr/sQKE9xtFuEmoQGlE1l6bGaDnnMLcYu+Asp3kDT0w4zYGsx 5r6XQVRH4+5N6eHZiaeYtFOujp5n+pjBaQK7wUUjDilPQ5QMzIuCL4YjVoylWiBNknvQWBXS lQCWmavOT9sttGQXdPCC5ynI+1ymZC1ORZKANLnRAb0NH/UCzcsstw2TAkFnMEbo9Zu9w7Kv AxBQXWeXhJI9XQssfrf4Gusdqx8nPEpfOqCtbbwJMATbHyqLt7/oz/5deGuwxgb65pWIzufa N7eop7uh+6bezi+rugUI+w6DABEBAAGJAjwEGAEIACYCGwwWIQQb2cqtc1xMOkYN/MpN3hD3 AP+DWgUCXw7HsgUJEqkpoQAKCRBN3hD3AP+DWrrpD/4qS3dyVRxDcDHIlmguXjC1Q5tZTwNB boaBTPHSy/Nksu0eY7x6HfQJ3xajVH32Ms6t1trDQmPx2iP5+7iDsb7OKAb5eOS8h+BEBDeq 3ecsQDv0fFJOA9ag5O3LLNk+3x3q7e0uo06XMaY7UHS341ozXUUI7wC7iKfoUTv03iO9El5f XpNMx/YrIMduZ2+nd9Di7o5+KIwlb2mAB9sTNHdMrXesX8eBL6T9b+MZJk+mZuPxKNVfEQMQ a5SxUEADIPQTPNvBewdeI80yeOCrN+Zzwy/Mrx9EPeu59Y5vSJOx/z6OUImD/GhX7Xvkt3kq Er5KTrJz3++B6SH9pum9PuoE/k+nntJkNMmQpR4MCBaV/J9gIOPGodDKnjdng+mXliF3Ptu6 3oxc2RCyGzTlxyMwuc2U5Q7KtUNTdDe8T0uE+9b8BLMVQDDfJjqY0VVqSUwImzTDLX9S4g/8 kC4HRcclk8hpyhY2jKGluZO0awwTIMgVEzmTyBphDg/Gx7dZU1Xf8HFuE+UZ5UDHDTnwgv7E th6RC9+WrhDNspZ9fJjKWRbveQgUFCpe1sa77LAw+XFrKmBHXp9ZVIe90RMe2tRL06BGiRZr jPrnvUsUUsjRoRNJjKKA/REq+sAnhkNPPZ/NNMjaZ5b8Tovi8C0tmxiCHaQYqj7G2rgnT0kt WNyWQQ== Organization: Red Hat GmbH Message-ID: <994394f3-c16d-911c-c9fc-d2280f32e7b1@redhat.com> Date: Thu, 15 Oct 2020 10:50:27 +0200 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:68.0) Gecko/20100101 Thunderbird/68.11.0 MIME-Version: 1.0 In-Reply-To: <20201015082808.GE86495@L-31X9LVDL-1304.local> Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: 8bit X-Scanned-By: MIMEDefang 2.84 on 10.5.11.22 Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 15.10.20 10:28, Wei Yang wrote: > On Mon, Oct 12, 2020 at 02:52:59PM +0200, David Hildenbrand wrote: >> Let's check by traversing busy system RAM resources instead, to avoid >> relying on memory block states. >> >> Don't use walk_system_ram_range(), as that works on pages and we want to >> use the bare addresses we have easily at hand. >> >> Cc: "Michael S. Tsirkin" >> Cc: Jason Wang >> Cc: Pankaj Gupta >> Signed-off-by: David Hildenbrand >> --- >> drivers/virtio/virtio_mem.c | 19 +++++++++++++++---- >> 1 file changed, 15 insertions(+), 4 deletions(-) >> >> diff --git a/drivers/virtio/virtio_mem.c b/drivers/virtio/virtio_mem.c >> index b3eebac7191f..6bbd1cfd10d3 100644 >> --- a/drivers/virtio/virtio_mem.c >> +++ b/drivers/virtio/virtio_mem.c >> @@ -1749,6 +1749,20 @@ static void virtio_mem_delete_resource(struct virtio_mem *vm) >> vm->parent_resource = NULL; >> } >> >> +static int virtio_mem_range_has_system_ram(struct resource *res, void *arg) >> +{ >> + return 1; >> +} >> + >> +static bool virtio_mem_has_memory_added(struct virtio_mem *vm) >> +{ >> + const unsigned long flags = IORESOURCE_SYSTEM_RAM | IORESOURCE_BUSY; >> + >> + return walk_iomem_res_desc(IORES_DESC_NONE, flags, vm->addr, >> + vm->addr + vm->region_size, NULL, >> + virtio_mem_range_has_system_ram) == 1; >> +} >> + >> static int virtio_mem_probe(struct virtio_device *vdev) >> { >> struct virtio_mem *vm; >> @@ -1870,10 +1884,7 @@ static void virtio_mem_remove(struct virtio_device *vdev) >> * the system. And there is no way to stop the driver/device from going >> * away. Warn at least. >> */ >> - if (vm->nb_mb_state[VIRTIO_MEM_MB_STATE_OFFLINE] || >> - vm->nb_mb_state[VIRTIO_MEM_MB_STATE_OFFLINE_PARTIAL] || >> - vm->nb_mb_state[VIRTIO_MEM_MB_STATE_ONLINE] || >> - vm->nb_mb_state[VIRTIO_MEM_MB_STATE_ONLINE_PARTIAL]) { >> + if (virtio_mem_has_memory_added(vm)) { > > I am not sure this would be more efficient. In general, no. However, this is a preparation for Big Block Mode, which won't have memory block states. (this path only triggers when unloading the driver - which most probably only ever happens during my testing ... :) and we don't really care about performance there) > >> dev_warn(&vdev->dev, "device still has system memory added\n"); >> } else { >> virtio_mem_delete_resource(vm); > > BTW, I got one question during review. > > Per my understanding, there are 4 states of a virtio memory block > > * OFFLINE[_PARTIAL] > * ONLINE[_PARTIAL] > > While, if my understanding is correct, those two offline states are transient. > If the required range is onlined, the state would be change to > ONLINE[_PARTIAL] respectively. If it is not, the state is reverted to UNUSED > or PLUGGED. Very right. > > What I am lost is why you do virtio_mem_mb_remove() on OFFLINE_PARTIAL memory > block? Since we wait for the workqueue finish its job. That's an interesting corner case. Assume you have a 128MB memory block but only 64MB are plugged. As long as we have our online_pages callback in place, we can hinder the unplugged 64MB from getting exposed to the buddy (virtio_mem_online_page_cb()). However, once we unloaded the driver, this is no longer the case. If someone would online that memory block, we would expose unplugged memory to the buddy - very bad. So we have to remove these partially plugged, offline memory blocks when losing control over them. I tried to document that via: "After we unregistered our callbacks, user space can online partially plugged offline blocks. Make sure to remove them." > > Also, during virtio_mem_remove(), we just handle OFFLINE_PARTIAL memory block. > How about memory block in other states? It is not necessary to remove > ONLINE[_PARTIAL] memroy blocks? Blocks that are fully plugged (ONLINE or OFFLINE) can get onlined/offlined without us having to care. Works fine - we only have to care about partially plugged blocks. While we *could* unplug OFFLINE blocks, there is no way we can deterministically offline+remove ONLINE blocks. So that memory has to stay, even after we unloaded the driver (similar to the dax/kmem driver). ONLINE_PARTIAL is already taken care of: it cannot get offlined anymore, as we still hold references to these struct pages (virtio_mem_set_fake_offline()), and as we no longer have the memory notifier in place, we can no longer agree to offline this memory (when going_offline). I tried to document that via "After we unregistered our callbacks, user space can no longer offline partially plugged online memory blocks. No need to worry about them." > > Thanks in advance, since I may missed some concepts. (force) driver unloading is a complicated corner case. Thanks! -- Thanks, David / dhildenb