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[70.31.27.79]) by smtp.gmail.com with ESMTPSA id b22-20020ac87fd6000000b003a6a4744432sm111027qtk.87.2022.12.13.08.31.32 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Tue, 13 Dec 2022 08:31:33 -0800 (PST) Date: Tue, 13 Dec 2022 11:31:32 -0500 From: Peter Xu To: Chuang Xu Cc: qemu-devel@nongnu.org, dgilbert@redhat.com, quintela@redhat.com, pbonzini@redhat.com, david@redhat.com, f4bug@amsat.org, mst@redhat.com, zhouyibo@bytedance.com Subject: Re: [RFC v3 2/3] virtio: support delay of checks in virtio_load() Message-ID: References: <20221213133510.1279488-1-xuchuangxclwt@bytedance.com> <20221213133510.1279488-3-xuchuangxclwt@bytedance.com> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline In-Reply-To: <20221213133510.1279488-3-xuchuangxclwt@bytedance.com> Received-SPF: pass client-ip=170.10.129.124; envelope-from=peterx@redhat.com; helo=us-smtp-delivery-124.mimecast.com X-Spam_score_int: -20 X-Spam_score: -2.1 X-Spam_bar: -- X-Spam_report: (-2.1 / 5.0 requ) BAYES_00=-1.9, DKIMWL_WL_HIGH=-0.001, DKIM_SIGNED=0.1, DKIM_VALID=-0.1, DKIM_VALID_AU=-0.1, DKIM_VALID_EF=-0.1, RCVD_IN_DNSWL_NONE=-0.0001, RCVD_IN_MSPIKE_H2=-0.001, SPF_HELO_NONE=0.001, SPF_PASS=-0.001 autolearn=ham autolearn_force=no X-Spam_action: no action X-BeenThere: qemu-devel@nongnu.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org On Tue, Dec 13, 2022 at 09:35:09PM +0800, Chuang Xu wrote: > Delay checks in virtio_load() to avoid possible address_space_to_flatview() call > during memory region's begin/commit. I didn't notice virtio has the vm change handler already, looks good to reuse it. :) A few more comments though (before some real virtio developers chim im). > > Signed-off-by: Chuang Xu > --- > hw/virtio/virtio.c | 37 +++++++++++++++++++++++++++---------- > include/hw/virtio/virtio.h | 2 ++ > 2 files changed, 29 insertions(+), 10 deletions(-) > > diff --git a/hw/virtio/virtio.c b/hw/virtio/virtio.c > index eb6347ab5d..f556e565c6 100644 > --- a/hw/virtio/virtio.c > +++ b/hw/virtio/virtio.c > @@ -3642,8 +3642,26 @@ int virtio_load(VirtIODevice *vdev, QEMUFile *f, int version_id) > vdev->start_on_kick = true; > } > > + vdev->delay_check = true; > + > + if (vdc->post_load) { > + ret = vdc->post_load(vdev); > + if (ret) { > + return ret; > + } > + } > + > + return 0; > +} > + > +static void virtio_load_check_delay(VirtIODevice *vdev) > +{ > RCU_READ_LOCK_GUARD(); > - for (i = 0; i < num; i++) { > + for (int i = 0; i < VIRTIO_QUEUE_MAX; i++) { > + if (vdev->vq[i].vring.num == 0) { > + break; > + } > + > if (vdev->vq[i].vring.desc) { > uint16_t nheads; > > @@ -3696,19 +3714,12 @@ int virtio_load(VirtIODevice *vdev, QEMUFile *f, int version_id) > i, vdev->vq[i].vring.num, > vdev->vq[i].last_avail_idx, > vdev->vq[i].used_idx); > - return -1; > + abort(); This is when the switchover finished. I'm not sure how severe this is and whether there can be something to remedy - abort() is probably the least we want to do here, since the admin may not want to crash the whole VM due to one vring failure on one device. > } > } > } > > - if (vdc->post_load) { > - ret = vdc->post_load(vdev); > - if (ret) { > - return ret; > - } > - } > - > - return 0; > + return; > } > > void virtio_cleanup(VirtIODevice *vdev) > @@ -3722,6 +3733,11 @@ static void virtio_vmstate_change(void *opaque, bool running, RunState state) > BusState *qbus = qdev_get_parent_bus(DEVICE(vdev)); > VirtioBusClass *k = VIRTIO_BUS_GET_CLASS(qbus); > bool backend_run = running && virtio_device_started(vdev, vdev->status); > + > + if (vdev->delay_check) { > + virtio_load_check_delay(vdev); > + vdev->delay_check = false; > + } > vdev->vm_running = running; > > if (backend_run) { > @@ -3789,6 +3805,7 @@ void virtio_init(VirtIODevice *vdev, uint16_t device_id, size_t config_size) > virtio_vmstate_change, vdev); > vdev->device_endian = virtio_default_endian(); > vdev->use_guest_notifier_mask = true; > + vdev->delay_check = false; > } > > /* > diff --git a/include/hw/virtio/virtio.h b/include/hw/virtio/virtio.h > index acfd4df125..269e80d04a 100644 > --- a/include/hw/virtio/virtio.h > +++ b/include/hw/virtio/virtio.h > @@ -135,6 +135,8 @@ struct VirtIODevice > AddressSpace *dma_as; > QLIST_HEAD(, VirtQueue) *vector_queues; > QTAILQ_ENTRY(VirtIODevice) next; > + /* @delay_check: delay checks in virtio_load */ > + bool delay_check; I think it covers more than the check? It also initializes variables like used_idx and shadow_avail_idx. I'm not sure how vital they are, but I'd just avoid using the word "check" if not sure (e.g. "load_delay", or "load_finalize"?). > }; > > struct VirtioDeviceClass { > -- > 2.20.1 > -- Peter Xu