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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: <20240710073925-mutt-send-email-mst@kernel.org> References: <20240710063601.2000149-1-jiri@resnulli.us> <20240710063601.2000149-13-jiri@resnulli.us> Precedence: bulk X-Mailing-List: virtualization@lists.linux.dev List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 In-Reply-To: <20240710063601.2000149-13-jiri@resnulli.us> 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 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. You need to add a callback and signal the completion. -- MST