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Tsirkin" To: Jiri Pirko Cc: virtualization@lists.linux.dev, jasowang@redhat.com, xuanzhuo@linux.alibaba.com, eperezma@redhat.com, parav@nvidia.com, feliu@nvidia.com, hengqi@linux.alibaba.com Subject: Re: [PATCH virtio v2 12/13] virtio_pci_modern: use completion instead of busy loop to wait on admin cmd result Message-ID: <20240710090418-mutt-send-email-mst@kernel.org> References: <20240710063601.2000149-1-jiri@resnulli.us> <20240710063601.2000149-13-jiri@resnulli.us> <20240710073925-mutt-send-email-mst@kernel.org> Precedence: bulk X-Mailing-List: virtualization@lists.linux.dev List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 In-Reply-To: X-Mimecast-Spam-Score: 0 X-Mimecast-Originator: redhat.com Content-Type: text/plain; charset=us-ascii Content-Disposition: inline On Wed, Jul 10, 2024 at 03:03:33PM +0200, Jiri Pirko wrote: > Wed, Jul 10, 2024 at 01:47:22PM CEST, mst@redhat.com wrote: > >On Wed, Jul 10, 2024 at 08:36:00AM +0200, Jiri Pirko wrote: > >> From: Jiri Pirko > >> > >> Currently, the code waits in a busy loop on every admin virtqueue issued > >> command to get a reply. That prevents callers from issuing multiple > >> commands in parallel. > >> > >> To overcome this limitation, introduce a virtqueue event callback for > >> admin virtqueue. For every issued command, use completion mechanism > >> to wait on a reply. In the event callback, trigger the completion > >> is done for every incoming reply. > >> > >> Alongside with that, introduce a spin lock to protect the admin > >> virtqueue operations. > >> > >> Signed-off-by: Jiri Pirko > >> --- > >> v1->v2: > >> - rebased on top of newly added patches > >> - rebased on top of changes in previous patches (vq info, vqs[]) > >> - removed WARN_ON_ONCE() when calling virtqueue_kick() > >> - added virtqueue_is_broken check in virtqueue_exec_admin_cmd() loop > >> - added vp_modern_avq_cleanup() implementation to handle surprise > >> removal case > >> --- > >> drivers/virtio/virtio_pci_common.c | 13 ++++-- > >> drivers/virtio/virtio_pci_common.h | 3 ++ > >> drivers/virtio/virtio_pci_modern.c | 74 +++++++++++++++++++++++++----- > >> include/linux/virtio.h | 3 ++ > >> 4 files changed, 77 insertions(+), 16 deletions(-) > >> > >> diff --git a/drivers/virtio/virtio_pci_common.c b/drivers/virtio/virtio_pci_common.c > >> index 267643bb1cd5..c44d8ba00c02 100644 > >> --- a/drivers/virtio/virtio_pci_common.c > >> +++ b/drivers/virtio/virtio_pci_common.c > >> @@ -395,6 +395,8 @@ static int vp_find_vqs_msix(struct virtio_device *vdev, unsigned int nvqs, > >> if (vqi->name && vqi->callback) > >> ++nvectors; > >> } > >> + if (avq_num && vector_policy == VP_VQ_VECTOR_POLICY_EACH) > >> + ++nvectors; > >> } else { > >> /* Second best: one for change, shared for all vqs. */ > >> nvectors = 2; > >> @@ -425,9 +427,9 @@ static int vp_find_vqs_msix(struct virtio_device *vdev, unsigned int nvqs, > >> if (!avq_num) > >> return 0; > >> sprintf(avq->name, "avq.%u", avq->vq_index); > >> - vq = vp_find_one_vq_msix(vdev, avq->vq_index, NULL, avq->name, false, > >> - true, &allocated_vectors, vector_policy, > >> - &vp_dev->admin_vq.info); > >> + vq = vp_find_one_vq_msix(vdev, avq->vq_index, vp_modern_avq_done, > >> + avq->name, false, true, &allocated_vectors, > >> + vector_policy, &vp_dev->admin_vq.info); > >> if (IS_ERR(vq)) { > >> err = PTR_ERR(vq); > >> goto error_find; > >> @@ -486,8 +488,9 @@ static int vp_find_vqs_intx(struct virtio_device *vdev, unsigned int nvqs, > >> if (!avq_num) > >> return 0; > >> sprintf(avq->name, "avq.%u", avq->vq_index); > >> - vq = vp_setup_vq(vdev, queue_idx++, NULL, avq->name, false, > >> - VIRTIO_MSI_NO_VECTOR, &vp_dev->admin_vq.info); > >> + vq = vp_setup_vq(vdev, queue_idx++, vp_modern_avq_done, avq->name, > >> + false, VIRTIO_MSI_NO_VECTOR, > >> + &vp_dev->admin_vq.info); > >> if (IS_ERR(vq)) { > >> err = PTR_ERR(vq); > >> goto out_del_vqs; > >> diff --git a/drivers/virtio/virtio_pci_common.h b/drivers/virtio/virtio_pci_common.h > >> index de59bb06ec3c..90df381fbbcf 100644 > >> --- a/drivers/virtio/virtio_pci_common.h > >> +++ b/drivers/virtio/virtio_pci_common.h > >> @@ -47,6 +47,8 @@ struct virtio_pci_admin_vq { > >> struct virtio_pci_vq_info *info; > >> /* serializing admin commands execution. */ > >> struct mutex cmd_lock; > >> + /* Protects virtqueue access. */ > >> + spinlock_t lock; > >> u64 supported_cmds; > >> /* Name of the admin queue: avq.$vq_index. */ > >> char name[10]; > >> @@ -178,6 +180,7 @@ struct virtio_device *virtio_pci_vf_get_pf_dev(struct pci_dev *pdev); > >> #define VIRTIO_ADMIN_CMD_BITMAP 0 > >> #endif > >> > >> +void vp_modern_avq_done(struct virtqueue *vq); > >> int vp_modern_admin_cmd_exec(struct virtio_device *vdev, > >> struct virtio_admin_cmd *cmd); > >> > >> diff --git a/drivers/virtio/virtio_pci_modern.c b/drivers/virtio/virtio_pci_modern.c > >> index 0fd344d1eaf9..608df3263df1 100644 > >> --- a/drivers/virtio/virtio_pci_modern.c > >> +++ b/drivers/virtio/virtio_pci_modern.c > >> @@ -53,6 +53,23 @@ static bool vp_is_avq(struct virtio_device *vdev, unsigned int index) > >> return index == vp_dev->admin_vq.vq_index; > >> } > >> > >> +void vp_modern_avq_done(struct virtqueue *vq) > >> +{ > >> + struct virtio_pci_device *vp_dev = to_vp_device(vq->vdev); > >> + struct virtio_pci_admin_vq *admin_vq = &vp_dev->admin_vq; > >> + struct virtio_admin_cmd *cmd; > >> + unsigned long flags; > >> + unsigned int len; > >> + > >> + spin_lock_irqsave(&admin_vq->lock, flags); > >> + do { > >> + virtqueue_disable_cb(vq); > >> + while ((cmd = virtqueue_get_buf(vq, &len))) > >> + complete(&cmd->completion); > >> + } while (!virtqueue_enable_cb(vq)); > >> + spin_unlock_irqrestore(&admin_vq->lock, flags); > >> +} > >> + > >> static int virtqueue_exec_admin_cmd(struct virtio_pci_admin_vq *admin_vq, > >> u16 opcode, > >> struct scatterlist **sgs, > >> @@ -61,7 +78,8 @@ static int virtqueue_exec_admin_cmd(struct virtio_pci_admin_vq *admin_vq, > >> struct virtio_admin_cmd *cmd) > >> { > >> struct virtqueue *vq; > >> - int ret, len; > >> + unsigned long flags; > >> + int ret; > >> > >> vq = admin_vq->info->vq; > >> if (!vq) > >> @@ -72,21 +90,33 @@ static int virtqueue_exec_admin_cmd(struct virtio_pci_admin_vq *admin_vq, > >> !((1ULL << opcode) & admin_vq->supported_cmds)) > >> return -EOPNOTSUPP; > >> > >> - ret = virtqueue_add_sgs(vq, sgs, out_num, in_num, cmd, GFP_KERNEL); > >> - if (ret < 0) > >> - return -EIO; > >> + init_completion(&cmd->completion); > >> > >> - if (unlikely(!virtqueue_kick(vq))) > >> +again: > >> + if (virtqueue_is_broken(vq)) > >> return -EIO; > >> > >> - while (!virtqueue_get_buf(vq, &len) && > >> - !virtqueue_is_broken(vq)) > >> - cpu_relax(); > >> + spin_lock_irqsave(&admin_vq->lock, flags); > >> + ret = virtqueue_add_sgs(vq, sgs, out_num, in_num, cmd, GFP_KERNEL); > >> + if (ret < 0) { > >> + if (ret == -ENOSPC) { > >> + spin_unlock_irqrestore(&admin_vq->lock, flags); > >> + cpu_relax(); > >> + goto again; > >> + } > >> + goto unlock_err; > >> + } > >> + if (!virtqueue_kick(vq)) > >> + goto unlock_err; > >> + spin_unlock_irqrestore(&admin_vq->lock, flags); > >> > >> - if (virtqueue_is_broken(vq)) > >> - return -EIO; > >> + wait_for_completion(&cmd->completion); > >> > >> - return 0; > >> + return cmd->ret; > >> + > >> +unlock_err: > >> + spin_unlock_irqrestore(&admin_vq->lock, flags); > >> + return -EIO; > >> } > >> > >> int vp_modern_admin_cmd_exec(struct virtio_device *vdev, > >> @@ -209,6 +239,25 @@ static void vp_modern_avq_activate(struct virtio_device *vdev) > >> virtio_pci_admin_cmd_list_init(vdev); > >> } > >> > >> +static void vp_modern_avq_cleanup(struct virtio_device *vdev) > >> +{ > >> + struct virtio_pci_device *vp_dev = to_vp_device(vdev); > >> + struct virtio_admin_cmd *cmd; > >> + struct virtqueue *vq; > >> + > >> + if (!virtio_has_feature(vdev, VIRTIO_F_ADMIN_VQ)) > >> + return; > >> + > >> + vq = vp_dev->vqs[vp_dev->admin_vq.vq_index]->vq; > >> + if (!vq) > >> + return; > >> + > >> + while ((cmd = virtqueue_detach_unused_buf(vq))) { > >> + cmd->ret = -EIO; > >> + complete(&cmd->completion); > >> + } > >> +} > >> + > > > > > >I think surprise removal is still broken with this. > > Why do you think so? I will drain the remaining buffers from the queue > and complete them all. What's missing? You have this: > >> + wait_for_completion(&cmd->completion); if surprise removal triggers after you submitted command but before it was used, no callback triggers and so no completion either. > > >You need to add a callback and signal the completion. > > Callback to what? for example, remove callback can signal completion. > > > > > > >-- > >MST > >