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[83.35.24.93]) by smtp.gmail.com with ESMTPSA id n8sm1603258wmc.45.2021.06.22.00.29.35 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Tue, 22 Jun 2021 00:29:35 -0700 (PDT) Subject: Re: [PATCH v2] block/nvme: Fix VFIO_MAP_DMA failed: No space left on device To: Fam Zheng References: <20210621093240.4170701-1-philmd@redhat.com> <9A674DF3-041E-4E7C-BB49-481AA77B1F7B@euphon.net> <6b77db0c-8625-992e-8546-15b9a24ae928@redhat.com> <0EF3A65E-39CB-4114-8572-001C2DF05863@euphon.net> From: =?UTF-8?Q?Philippe_Mathieu-Daud=c3=a9?= Message-ID: Date: Tue, 22 Jun 2021 09:29:34 +0200 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:78.0) Gecko/20100101 Thunderbird/78.10.1 MIME-Version: 1.0 In-Reply-To: <0EF3A65E-39CB-4114-8572-001C2DF05863@euphon.net> Authentication-Results: relay.mimecast.com; auth=pass smtp.auth=CUSA124A263 smtp.mailfrom=philmd@redhat.com X-Mimecast-Spam-Score: 0 X-Mimecast-Originator: redhat.com Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: 8bit Received-SPF: pass client-ip=170.10.133.124; envelope-from=philmd@redhat.com; helo=us-smtp-delivery-124.mimecast.com X-Spam_score_int: -31 X-Spam_score: -3.2 X-Spam_bar: --- X-Spam_report: (-3.2 / 5.0 requ) BAYES_00=-1.9, DKIMWL_WL_HIGH=-0.373, DKIM_SIGNED=0.1, DKIM_VALID=-0.1, DKIM_VALID_AU=-0.1, DKIM_VALID_EF=-0.1, NICE_REPLY_A=-0.001, RCVD_IN_DNSWL_LOW=-0.7, RCVD_IN_MSPIKE_H4=0.001, RCVD_IN_MSPIKE_WL=0.001, SPF_HELO_NONE=0.001, SPF_PASS=-0.001 autolearn=unavailable autolearn_force=no X-Spam_action: no action X-BeenThere: qemu-devel@nongnu.org X-Mailman-Version: 2.1.23 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: Kevin Wolf , qemu-block@nongnu.org, qemu-devel@nongnu.org, =?UTF-8?B?TWljaGFsIFByw612b3puw61r?= , qemu-stable@nongnu.org, Maxim Levitsky , Eric Auger , Alex Williamson , Stefan Hajnoczi , Max Reitz Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: "Qemu-devel" On 6/21/21 5:36 PM, Fam Zheng wrote: >> On 21 Jun 2021, at 16:13, Philippe Mathieu-Daudé wrote: >> On 6/21/21 3:18 PM, Fam Zheng wrote: >>>> On 21 Jun 2021, at 10:32, Philippe Mathieu-Daudé wrote: >>>> >>>> When the NVMe block driver was introduced (see commit bdd6a90a9e5, >>>> January 2018), Linux VFIO_IOMMU_MAP_DMA ioctl was only returning >>>> -ENOMEM in case of error. The driver was correctly handling the >>>> error path to recycle its volatile IOVA mappings. >>>> >>>> To fix CVE-2019-3882, Linux commit 492855939bdb ("vfio/type1: Limit >>>> DMA mappings per container", April 2019) added the -ENOSPC error to >>>> signal the user exhausted the DMA mappings available for a container. >>>> >>>> The block driver started to mis-behave: >>>> >>>> qemu-system-x86_64: VFIO_MAP_DMA failed: No space left on device >>>> (qemu) >>>> (qemu) info status >>>> VM status: paused (io-error) >>>> (qemu) c >>>> VFIO_MAP_DMA failed: No space left on device >>>> qemu-system-x86_64: block/block-backend.c:1968: blk_get_aio_context: Assertion `ctx == blk->ctx' failed. >>> >>> Hi Phil, >>> >>> >>> The diff looks good to me, but I’m not sure what exactly caused the assertion failure. There is `if (r) { goto fail; }` that handles -ENOSPC before, so it should be treated as a general case. What am I missing? >> >> Good catch, ENOSPC ends setting BLOCK_DEVICE_IO_STATUS_NOSPACE >> -> BLOCK_ERROR_ACTION_STOP, so the VM is paused with DMA mapping >> exhausted. I don't understand the full "VM resume" path, but this >> is not what we want (IO_NOSPACE is to warn the operator to add >> more storage and resume, which is pointless in our case, resuming >> won't help until we flush the mappings). >> >> IIUC what we want is return ENOMEM to set BLOCK_DEVICE_IO_STATUS_FAILED. > > I agree with that. It just makes me feel there’s another bug in the resuming code path. Can you get a backtrace? It seems the resuming code path bug has been fixed elsewhere: (qemu) info status info status VM status: paused (io-error) (qemu) c c 2021-06-22T07:27:00.745466Z qemu-system-x86_64: VFIO_MAP_DMA failed: No space left on device (qemu) info status info status VM status: paused (io-error) (qemu) c c 2021-06-22T07:27:12.458137Z qemu-system-x86_64: VFIO_MAP_DMA failed: No space left on device (qemu) c c 2021-06-22T07:27:13.439167Z qemu-system-x86_64: VFIO_MAP_DMA failed: No space left on device (qemu) c c 2021-06-22T07:27:14.272071Z qemu-system-x86_64: VFIO_MAP_DMA failed: No space left on device (qemu)