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=-2.4 required=3.0 tests=DKIMWL_WL_HIGH,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI, SPF_HELO_NONE,SPF_PASS,USER_AGENT_SANE_1 autolearn=no 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 E1C8EC433E1 for ; Thu, 14 May 2020 12:20:25 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id B3FE3206DA for ; Thu, 14 May 2020 12:20:25 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (1024-bit key) header.d=redhat.com header.i=@redhat.com header.b="dYXpXTtC" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1727861AbgENMUY (ORCPT ); Thu, 14 May 2020 08:20:24 -0400 Received: from us-smtp-2.mimecast.com ([205.139.110.61]:43774 "EHLO us-smtp-1.mimecast.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726199AbgENMUY (ORCPT ); Thu, 14 May 2020 08:20:24 -0400 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1589458821; 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=9aCz4qvsPpwDokPvw5swdrzksgBU0j0lrQXHgXqHs5M=; b=dYXpXTtC1SSAWOKYAyYi+u8VRvcGv3Yi2JDsvOP09s+oeA0QVKudzDoC+ngWXZiYOyFA/0 h49bz7Ur6BdbBKlap+wtth9NgwErNi+T1SYL5IUPm5Su81KoC/zILTNqfqO+HTxeftJQDC x7sD3VzYcFY6qOLTEkgPms5wKNxQ7JY= 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-20-gw2F4bHnNB6zA23Q_4lAsg-1; Thu, 14 May 2020 08:20:17 -0400 X-MC-Unique: gw2F4bHnNB6zA23Q_4lAsg-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 D5E121902EA7; Thu, 14 May 2020 12:20:12 +0000 (UTC) Received: from [10.36.114.168] (ovpn-114-168.ams2.redhat.com [10.36.114.168]) by smtp.corp.redhat.com (Postfix) with ESMTP id 45F1A1001920; Thu, 14 May 2020 12:19:52 +0000 (UTC) Subject: Re: [virtio-dev] [PATCH v3 00/15] virtio-mem: paravirtualized memory From: David Hildenbrand To: teawater Cc: LKML , Linux MM , virtio-dev@lists.oasis-open.org, Linux Virtualization , kvm@vger.kernel.org, Michal Hocko , Andrew Morton , "Michael S . Tsirkin" , Sebastien Boeuf , Samuel Ortiz , Robert Bradford , Luiz Capitulino , Pankaj Gupta , Igor Mammedov , "Dr . David Alan Gilbert" , Alexander Duyck , Alexander Potapenko , Anshuman Khandual , Anthony Yznaga , Dan Williams , Dave Young , Jason Wang , Johannes Weiner , Juergen Gross , Konrad Rzeszutek Wilk , Len Brown , Mel Gorman , Michal Hocko , Mike Rapoport , Oscar Salvador , Oscar Salvador , Pavel Tatashin , Pavel Tatashin , Pingfan Liu , Qian Cai , "Rafael J. Wysocki" , "Rafael J. Wysocki" , Stefan Hajnoczi , Vlastimil Babka , Wei Yang References: <20200507103119.11219-1-david@redhat.com> <7848642F-6AA7-4B5E-AE0E-DB0857C94A93@linux.alibaba.com> <31c5d2f9-c104-53e8-d9c8-cb45f7507c85@redhat.com> <389b6bdc-b196-e4b9-b6be-dcac57524fdf@redhat.com> <3c82e149-6c42-690e-9d58-bb8e69870fe0@redhat.com> 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 ZW5icmFuZCA8ZGF2aWRAcmVkaGF0LmNvbT6JAlgEEwEIAEICGwMFCQlmAYAGCwkIBwMCBhUI AgkKCwQWAgMBAh4BAheAFiEEG9nKrXNcTDpGDfzKTd4Q9wD/g1oFAl3pImkCGQEACgkQTd4Q 9wD/g1o+VA//SFvIHUAvul05u6wKv/pIR6aICPdpF9EIgEU448g+7FfDgQwcEny1pbEzAmiw zAXIQ9H0NZh96lcq+yDLtONnXk/bEYWHHUA014A1wqcYNRY8RvY1+eVHb0uu0KYQoXkzvu+s Dncuguk470XPnscL27hs8PgOP6QjG4jt75K2LfZ0eAqTOUCZTJxA8A7E9+XTYuU0hs7QVrWJ jQdFxQbRMrYz7uP8KmTK9/Cnvqehgl4EzyRaZppshruKMeyheBgvgJd5On1wWq4ZUV5PFM4x II3QbD3EJfWbaJMR55jI9dMFa+vK7MFz3rhWOkEx/QR959lfdRSTXdxs8V3zDvChcmRVGN8U Vo93d1YNtWnA9w6oCW1dnDZ4kgQZZSBIjp6iHcA08apzh7DPi08jL7M9UQByeYGr8KuR4i6e RZI6xhlZerUScVzn35ONwOC91VdYiQgjemiVLq1WDDZ3B7DIzUZ4RQTOaIWdtXBWb8zWakt/ ztGhsx0e39Gvt3391O1PgcA7ilhvqrBPemJrlb9xSPPRbaNAW39P8ws/UJnzSJqnHMVxbRZC Am4add/SM+OCP0w3xYss1jy9T+XdZa0lhUvJfLy7tNcjVG/sxkBXOaSC24MFPuwnoC9WvCVQ ZBxouph3kqc4Dt5X1EeXVLeba+466P1fe1rC8MbcwDkoUo65Ag0EVcufkQEQAOfX3n0g0fZz 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+w6DABEBAAGJAiUEGAECAA8FAlXLn5ECGwwFCQlmAYAACgkQTd4Q 9wD/g1qA6w/+M+ggFv+JdVsz5+ZIc6MSyGUozASX+bmIuPeIecc9UsFRatc91LuJCKMkD9Uv GOcWSeFpLrSGRQ1Z7EMzFVU//qVs6uzhsNk0RYMyS0B6oloW3FpyQ+zOVylFWQCzoyyf227y GW8HnXunJSC+4PtlL2AY4yZjAVAPLK2l6mhgClVXTQ/S7cBoTQKP+jvVJOoYkpnFxWE9pn4t H5QIFk7Ip8TKr5k3fXVWk4lnUi9MTF/5L/mWqdyIO1s7cjharQCstfWCzWrVeVctpVoDfJWp 4LwTuQ5yEM2KcPeElLg5fR7WB2zH97oI6/Ko2DlovmfQqXh9xWozQt0iGy5tWzh6I0JrlcxJ ileZWLccC4XKD1037Hy2FLAjzfoWgwBLA6ULu0exOOdIa58H4PsXtkFPrUF980EEibUp0zFz GotRVekFAceUaRvAj7dh76cToeZkfsjAvBVb4COXuhgX6N4pofgNkW2AtgYu1nUsPAo+NftU CxrhjHtLn4QEBpkbErnXQyMjHpIatlYGutVMS91XTQXYydCh5crMPs7hYVsvnmGHIaB9ZMfB njnuI31KBiLUks+paRkHQlFcgS2N3gkRBzH7xSZ+t7Re3jvXdXEzKBbQ+dC3lpJB0wPnyMcX FOTT3aZT7IgePkt5iC/BKBk3hqKteTnJFeVIT7EC+a6YUFg= Organization: Red Hat GmbH Message-ID: Date: Thu, 14 May 2020 14:19:51 +0200 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:68.0) Gecko/20100101 Thunderbird/68.7.0 MIME-Version: 1.0 In-Reply-To: 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 Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 14.05.20 13:47, David Hildenbrand wrote: > On 14.05.20 13:10, David Hildenbrand wrote: >> On 14.05.20 12:12, David Hildenbrand wrote: >>> On 14.05.20 12:02, teawater wrote: >>>> >>>> >>>>> 2020年5月14日 16:48，David Hildenbrand 写道： >>>>> >>>>> On 14.05.20 08:44, teawater wrote: >>>>>> Hi David, >>>>>> >>>>>> I got a kernel warning with v2 and v3. >>>>> >>>>> Hi Hui, >>>>> >>>>> thanks for playing with the latest versions. Surprisingly, I can >>>>> reproduce even by hotplugging a DIMM instead as well - that's good, so >>>>> it's not related to virtio-mem, lol. Seems to be some QEMU setup issue >>>>> with older machine types. >>>>> >>>>> Can you switch to a newer qemu machine version, especially >>>>> pc-i440fx-5.0? Both, hotplugging DIMMs and virtio-mem works for me with >>>>> that QEMU machine just fine. >>>> >>>> I still could reproduce this issue with pc-i440fx-5.0 or pc. Did I miss anything? >>>> >>> >>> Below I don't even see virtio_mem. I had to repair the image (filesystem >>> fsck) because it was broken, can you try that as well? >>> >>> Also, it would be great if you could test with v4. >>> >> >> Correction, something seems to be broken either in QEMU or the kernel. Once I >> define a DIMM so it's added and online during boot, I get these issues: >> >> (I have virtio-mem v4 installed in the guest) >> >> #! /bin/bash >> sudo x86_64-softmmu/qemu-system-x86_64 \ >> -machine pc-i440fx-5.0,accel=kvm,usb=off \ >> -cpu host \ >> -no-reboot \ >> -nographic \ >> -device ide-hd,drive=hd \ >> -drive if=none,id=hd,file=/home/dhildenb/git/Fedora-Cloud-Base-31-1.9.x86_64.qcow2,format=qcow2 \ >> -m 1g,slots=10,maxmem=2G \ >> -smp 1 \ >> -object memory-backend-ram,id=mem0,size=256m \ >> -device pc-dimm,id=dimm0,memdev=mem0 \ >> -s \ >> -monitor unix:/var/tmp/monitor,server,nowait >> >> >> Without the DIMM it seems to work just fine. >> > > And another correction. > > Using QEMU v5.0.0, Linux 5.7-rc5, untouched > Fedora-Cloud-Base-32-1.6.x86_64.qcow2, I get even without any memory hotplug: > > #! /bin/bash > sudo x86_64-softmmu/qemu-system-x86_64 \ > -machine pc-i440fx-5.0,accel=kvm,usb=off \ > -cpu host \ > -no-reboot \ > -nographic \ > -device ide-hd,drive=hd \ > -drive if=none,id=hd,file=/home/dhildenb/git/Fedora-Cloud-Base-32-1.6.x86_64.qcow2,format=qcow2 \ > -m 5g,slots=10,maxmem=6G \ > -smp 1 \ > -s \ > -kernel /home/dhildenb/git/linux/arch/x86/boot/bzImage \ > -append "console=ttyS0 rd.shell nokaslr swiotlb=noforce" \ > -monitor unix:/var/tmp/monitor,server,nowait > > > Observe how big the initial RAM even is! > > > So this is no DIMM/hotplug/virtio_mem issue. With memory hotplug, it seems to get > more likely to trigger if "swiotlb=noforce" is not specified. > > "swiotlb=noforce" seems to trigger some pre-existing issue here. Without > "swiotlb=noforce", I was only able to observe this via pc-i440fx-2.1, > (talking to myself :) ) I think I finally understood why using "swiotlb=noforce" with hotplugged memory is wrong - or with memory > 3GB. Via "swiotlb=noforce" you tell the system to "Never use bounce buffers (for debugging)". This works as long as all memory is DMA memory (e.g., < 3GB) AFAIK. "If specified, trying to map memory that cannot be used with DMA will fail, and a rate-limited warning will be printed." Hotplugged memory (under QEMU) is never added below 4GB, because of the PCI hole. So both, memory from DIMMs and from virtio-mem will end up at or above 4GB. To make a device use that memory, you need bounce buffers. Hotplugged memory is never DMA memory. -- Thanks, David / dhildenb From mboxrd@z Thu Jan 1 00:00:00 1970 From: David Hildenbrand Subject: Re: [PATCH v3 00/15] virtio-mem: paravirtualized memory Date: Thu, 14 May 2020 14:19:51 +0200 Message-ID: References: <20200507103119.11219-1-david@redhat.com> <7848642F-6AA7-4B5E-AE0E-DB0857C94A93@linux.alibaba.com> <31c5d2f9-c104-53e8-d9c8-cb45f7507c85@redhat.com> <389b6bdc-b196-e4b9-b6be-dcac57524fdf@redhat.com> <3c82e149-6c42-690e-9d58-bb8e69870fe0@redhat.com> Mime-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: 8bit Return-path: Sender: List-Post: List-Help: List-Unsubscribe: List-Subscribe: In-Reply-To: Content-Language: en-US To: teawater Cc: LKML , Linux MM , virtio-dev@lists.oasis-open.org, Linux Virtualization , kvm@vger.kernel.org, Michal Hocko , Andrew Morton , "Michael S . Tsirkin" , Sebastien Boeuf , Samuel Ortiz , Robert Bradford , Luiz Capitulino , Pankaj Gupta , Igor Mammedov , "Dr . David Alan Gilbert" , Alexander Duyck , Alexander Potapenko , Anshuman Khandual , Anthony Yznaga , Dan Williams , Dave Young Jason Wang List-Id: virtualization@lists.linuxfoundation.org On 14.05.20 13:47, David Hildenbrand wrote: > On 14.05.20 13:10, David Hildenbrand wrote: >> On 14.05.20 12:12, David Hildenbrand wrote: >>> On 14.05.20 12:02, teawater wrote: >>>> >>>> >>>>> 2020年5月14日 16:48，David Hildenbrand 写道： >>>>> >>>>> On 14.05.20 08:44, teawater wrote: >>>>>> Hi David, >>>>>> >>>>>> I got a kernel warning with v2 and v3. >>>>> >>>>> Hi Hui, >>>>> >>>>> thanks for playing with the latest versions. Surprisingly, I can >>>>> reproduce even by hotplugging a DIMM instead as well - that's good, so >>>>> it's not related to virtio-mem, lol. Seems to be some QEMU setup issue >>>>> with older machine types. >>>>> >>>>> Can you switch to a newer qemu machine version, especially >>>>> pc-i440fx-5.0? Both, hotplugging DIMMs and virtio-mem works for me with >>>>> that QEMU machine just fine. >>>> >>>> I still could reproduce this issue with pc-i440fx-5.0 or pc. Did I miss anything? >>>> >>> >>> Below I don't even see virtio_mem. I had to repair the image (filesystem >>> fsck) because it was broken, can you try that as well? >>> >>> Also, it would be great if you could test with v4. >>> >> >> Correction, something seems to be broken either in QEMU or the kernel. Once I >> define a DIMM so it's added and online during boot, I get these issues: >> >> (I have virtio-mem v4 installed in the guest) >> >> #! /bin/bash >> sudo x86_64-softmmu/qemu-system-x86_64 \ >> -machine pc-i440fx-5.0,accel=kvm,usb=off \ >> -cpu host \ >> -no-reboot \ >> -nographic \ >> -device ide-hd,drive=hd \ >> -drive if=none,id=hd,file=/home/dhildenb/git/Fedora-Cloud-Base-31-1.9.x86_64.qcow2,format=qcow2 \ >> -m 1g,slots=10,maxmem=2G \ >> -smp 1 \ >> -object memory-backend-ram,id=mem0,size=256m \ >> -device pc-dimm,id=dimm0,memdev=mem0 \ >> -s \ >> -monitor unix:/var/tmp/monitor,server,nowait >> >> >> Without the DIMM it seems to work just fine. >> > > And another correction. > > Using QEMU v5.0.0, Linux 5.7-rc5, untouched > Fedora-Cloud-Base-32-1.6.x86_64.qcow2, I get even without any memory hotplug: > > #! /bin/bash > sudo x86_64-softmmu/qemu-system-x86_64 \ > -machine pc-i440fx-5.0,accel=kvm,usb=off \ > -cpu host \ > -no-reboot \ > -nographic \ > -device ide-hd,drive=hd \ > -drive if=none,id=hd,file=/home/dhildenb/git/Fedora-Cloud-Base-32-1.6.x86_64.qcow2,format=qcow2 \ > -m 5g,slots=10,maxmem=6G \ > -smp 1 \ > -s \ > -kernel /home/dhildenb/git/linux/arch/x86/boot/bzImage \ > -append "console=ttyS0 rd.shell nokaslr swiotlb=noforce" \ > -monitor unix:/var/tmp/monitor,server,nowait > > > Observe how big the initial RAM even is! > > > So this is no DIMM/hotplug/virtio_mem issue. With memory hotplug, it seems to get > more likely to trigger if "swiotlb=noforce" is not specified. > > "swiotlb=noforce" seems to trigger some pre-existing issue here. Without > "swiotlb=noforce", I was only able to observe this via pc-i440fx-2.1, > (talking to myself :) ) I think I finally understood why using "swiotlb=noforce" with hotplugged memory is wrong - or with memory > 3GB. Via "swiotlb=noforce" you tell the system to "Never use bounce buffers (for debugging)". This works as long as all memory is DMA memory (e.g., < 3GB) AFAIK. "If specified, trying to map memory that cannot be used with DMA will fail, and a rate-limited warning will be printed." Hotplugged memory (under QEMU) is never added below 4GB, because of the PCI hole. So both, memory from DIMMs and from virtio-mem will end up at or above 4GB. To make a device use that memory, you need bounce buffers. Hotplugged memory is never DMA memory. -- Thanks, David / dhildenb From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: virtio-dev-return-7342-cohuck=redhat.com@lists.oasis-open.org Sender: List-Post: List-Help: List-Unsubscribe: List-Subscribe: Received: from lists.oasis-open.org (oasis-open.org [10.110.1.242]) by lists.oasis-open.org (Postfix) with ESMTP id 3ADA8985FC7 for ; Thu, 14 May 2020 12:20:23 +0000 (UTC) From: David Hildenbrand References: <20200507103119.11219-1-david@redhat.com> <7848642F-6AA7-4B5E-AE0E-DB0857C94A93@linux.alibaba.com> <31c5d2f9-c104-53e8-d9c8-cb45f7507c85@redhat.com> <389b6bdc-b196-e4b9-b6be-dcac57524fdf@redhat.com> <3c82e149-6c42-690e-9d58-bb8e69870fe0@redhat.com> Message-ID: Date: Thu, 14 May 2020 14:19:51 +0200 MIME-Version: 1.0 In-Reply-To: Content-Language: en-US Subject: Re: [virtio-dev] [PATCH v3 00/15] virtio-mem: paravirtualized memory Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: quoted-printable To: teawater Cc: LKML , Linux MM , virtio-dev@lists.oasis-open.org, Linux Virtualization , kvm@vger.kernel.org, Michal Hocko , Andrew Morton , "Michael S . Tsirkin" , Sebastien Boeuf , Samuel Ortiz , Robert Bradford , Luiz Capitulino , Pankaj Gupta , Igor Mammedov , "Dr . David Alan Gilbert" , Alexander Duyck , Alexander Potapenko , Anshuman Khandual , Anthony Yznaga , Dan Williams , Dave Young , Jason Wang , Johannes Weiner , Juergen Gross , Konrad Rzeszutek Wilk , Len Brown , Mel Gorman , Michal Hocko , Mike Rapoport , Oscar Salvador , Oscar Salvador , Pavel Tatashin , Pavel Tatashin , Pingfan Liu , Qian Cai , "Rafael J. Wysocki" , "Rafael J. Wysocki" , Stefan Hajnoczi , Vlastimil Babka , Wei Yang List-ID: On 14.05.20 13:47, David Hildenbrand wrote: > On 14.05.20 13:10, David Hildenbrand wrote: >> On 14.05.20 12:12, David Hildenbrand wrote: >>> On 14.05.20 12:02, teawater wrote: >>>> >>>> >>>>> 2020=E5=B9=B45=E6=9C=8814=E6=97=A5 16:48=EF=BC=8CDavid Hildenbrand =E5=86=99=E9=81=93=EF=BC=9A >>>>> >>>>> On 14.05.20 08:44, teawater wrote: >>>>>> Hi David, >>>>>> >>>>>> I got a kernel warning with v2 and v3. >>>>> >>>>> Hi Hui, >>>>> >>>>> thanks for playing with the latest versions. Surprisingly, I can >>>>> reproduce even by hotplugging a DIMM instead as well - that's good, s= o >>>>> it's not related to virtio-mem, lol. Seems to be some QEMU setup issu= e >>>>> with older machine types. >>>>> >>>>> Can you switch to a newer qemu machine version, especially >>>>> pc-i440fx-5.0? Both, hotplugging DIMMs and virtio-mem works for me wi= th >>>>> that QEMU machine just fine. >>>> >>>> I still could reproduce this issue with pc-i440fx-5.0 or pc. Did I mi= ss anything? >>>> >>> >>> Below I don't even see virtio_mem. I had to repair the image (filesyste= m >>> fsck) because it was broken, can you try that as well? >>> >>> Also, it would be great if you could test with v4. >>> >> >> Correction, something seems to be broken either in QEMU or the kernel. O= nce I >> define a DIMM so it's added and online during boot, I get these issues: >> >> (I have virtio-mem v4 installed in the guest) >> >> #! /bin/bash >> sudo x86_64-softmmu/qemu-system-x86_64 \ >> -machine pc-i440fx-5.0,accel=3Dkvm,usb=3Doff \ >> -cpu host \ >> -no-reboot \ >> -nographic \ >> -device ide-hd,drive=3Dhd \ >> -drive if=3Dnone,id=3Dhd,file=3D/home/dhildenb/git/Fedora-Cloud-Base= -31-1.9.x86_64.qcow2,format=3Dqcow2 \ >> -m 1g,slots=3D10,maxmem=3D2G \ >> -smp 1 \ >> -object memory-backend-ram,id=3Dmem0,size=3D256m \ >> -device pc-dimm,id=3Ddimm0,memdev=3Dmem0 \ >> -s \ >> -monitor unix:/var/tmp/monitor,server,nowait >> >> >> Without the DIMM it seems to work just fine. >> >=20 > And another correction.=20 >=20 > Using QEMU v5.0.0, Linux 5.7-rc5, untouched > Fedora-Cloud-Base-32-1.6.x86_64.qcow2, I get even without any memory hotp= lug: >=20 > #! /bin/bash > sudo x86_64-softmmu/qemu-system-x86_64 \ > -machine pc-i440fx-5.0,accel=3Dkvm,usb=3Doff \ > -cpu host \ > -no-reboot \ > -nographic \ > -device ide-hd,drive=3Dhd \ > -drive if=3Dnone,id=3Dhd,file=3D/home/dhildenb/git/Fedora-Cloud-Base-= 32-1.6.x86_64.qcow2,format=3Dqcow2 \ > -m 5g,slots=3D10,maxmem=3D6G \ > -smp 1 \ > -s \ > -kernel /home/dhildenb/git/linux/arch/x86/boot/bzImage \ > -append "console=3DttyS0 rd.shell nokaslr swiotlb=3Dnoforce" \ > -monitor unix:/var/tmp/monitor,server,nowait >=20 >=20 > Observe how big the initial RAM even is! >=20 >=20 > So this is no DIMM/hotplug/virtio_mem issue. With memory hotplug, it seem= s to get > more likely to trigger if "swiotlb=3Dnoforce" is not specified. >=20 > "swiotlb=3Dnoforce" seems to trigger some pre-existing issue here. Withou= t > "swiotlb=3Dnoforce", I was only able to observe this via pc-i440fx-2.1, >=20 (talking to myself :) ) I think I finally understood why using "swiotlb=3Dnoforce" with hotplugged memory is wrong - or with memory > 3GB. Via "swiotlb=3Dnoforce" you tell the system to "Never use bounce buffers (for debugging)". This works as long as all memory is DMA memory (e.g., < 3GB) AFAIK. "If specified, trying to map memory that cannot be used with DMA will fail, and a rate-limited warning will be printed." Hotplugged memory (under QEMU) is never added below 4GB, because of the PCI hole. So both, memory from DIMMs and from virtio-mem will end up at or above 4GB. To make a device use that memory, you need bounce buffers. Hotplugged memory is never DMA memory. --=20 Thanks, David / dhildenb --------------------------------------------------------------------- To unsubscribe, e-mail: virtio-dev-unsubscribe@lists.oasis-open.org For additional commands, e-mail: virtio-dev-help@lists.oasis-open.org