On Mon, Jun 24, 2024 at 11:04:50AM +0200, Jiri Pirko wrote:
> From: Jiri Pirko <jiri@xxxxxxxxxx>
>
> 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 <jiri@xxxxxxxxxx>
> ---
> drivers/virtio/virtio_pci_common.c | 10 +++---
> drivers/virtio/virtio_pci_common.h | 3 ++
> drivers/virtio/virtio_pci_modern.c | 52 +++++++++++++++++++++++-------
> include/linux/virtio.h | 2 ++
> 4 files changed, 51 insertions(+), 16 deletions(-)
>
> diff --git a/drivers/virtio/virtio_pci_common.c b/drivers/virtio/virtio_pci_common.c
> index 07c0511f170a..5ff7304c7a2a 100644
> --- a/drivers/virtio/virtio_pci_common.c
> +++ b/drivers/virtio/virtio_pci_common.c
> @@ -346,6 +346,8 @@ static int vp_find_vqs_msix(struct virtio_device *vdev, unsigned int nvqs,
> for (i = 0; i < nvqs; ++i)
> if (names[i] && callbacks[i])
> ++nvectors;
> + if (avq_num)
> + ++nvectors;
> } else {
> /* Second best: one for change, shared for all vqs. */
> nvectors = 2;
> @@ -375,8 +377,8 @@ 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);
> - vqs[i] = vp_find_one_vq_msix(vdev, avq->vq_index, NULL, avq->name,
> - false, &allocated_vectors);
> + vqs[i] = vp_find_one_vq_msix(vdev, avq->vq_index, vp_modern_avq_done,
> + avq->name, false, &allocated_vectors);
> if (IS_ERR(vqs[i])) {
> err = PTR_ERR(vqs[i]);
> goto error_find;
> @@ -432,8 +434,8 @@ 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);
> - vqs[i] = vp_setup_vq(vdev, queue_idx++, NULL, avq->name,
> - false, VIRTIO_MSI_NO_VECTOR);
> + vqs[i] = vp_setup_vq(vdev, queue_idx++, vp_modern_avq_done,
> + avq->name, false, VIRTIO_MSI_NO_VECTOR);
> if (IS_ERR(vqs[i])) {
> err = PTR_ERR(vqs[i]);
> goto out_del_vqs;
> diff --git a/drivers/virtio/virtio_pci_common.h b/drivers/virtio/virtio_pci_common.h
> index b3ef76287b43..38a0b6df0844 100644
> --- a/drivers/virtio/virtio_pci_common.h
> +++ b/drivers/virtio/virtio_pci_common.h
> @@ -45,6 +45,8 @@ struct virtio_pci_vq_info {
> struct virtio_pci_admin_vq {
> /* 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];
> @@ -174,6 +176,7 @@ 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 b4041e541fc3..b9937e4b8a69 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_device *vp_dev,
> struct virtio_pci_admin_vq *admin_vq,
> u16 opcode,
> @@ -62,7 +79,8 @@ static int virtqueue_exec_admin_cmd(struct virtio_pci_device *vp_dev,
> struct virtio_admin_cmd *cmd)
> {
> struct virtqueue *vq;
> - int ret, len;
> + unsigned long flags;
> + int ret;
>
> vq = vp_dev->vqs[admin_vq->vq_index]->vq;
> if (!vq)
> @@ -73,21 +91,30 @@ static int virtqueue_exec_admin_cmd(struct virtio_pci_device *vp_dev,
> !((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;
> -
> - if (unlikely(!virtqueue_kick(vq)))
> - return -EIO;
> + init_completion(&cmd->completion);
>
> - while (!virtqueue_get_buf(vq, &len) &&
> - !virtqueue_is_broken(vq))
> - cpu_relax();
> +again:
> + 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 (WARN_ON_ONCE(!virtqueue_kick(vq)))
> + goto unlock_err;
This can actually happen with suprise removal.
So WARN_ON_ONCE isn't really appropriate I think.
> + spin_unlock_irqrestore(&admin_vq->lock, flags);
>
> - if (virtqueue_is_broken(vq))
> - return -EIO;
> + wait_for_completion(&cmd->completion);
>
> return 0;
> +
> +unlock_err:
> + spin_unlock_irqrestore(&admin_vq->lock, flags);
> + return -EIO;
> }
>
> int vp_modern_admin_cmd_exec(struct virtio_device *vdev,
> @@ -787,6 +814,7 @@ int virtio_pci_modern_probe(struct virtio_pci_device *vp_dev)
> vp_dev->isr = mdev->isr;
> vp_dev->vdev.id = mdev->id;
>
> + spin_lock_init(&vp_dev->admin_vq.lock);
> mutex_init(&vp_dev->admin_vq.cmd_lock);
> return 0;
> }
> diff --git a/include/linux/virtio.h b/include/linux/virtio.h
> index 26c4325aa373..5db8ee175e71 100644
> --- a/include/linux/virtio.h
> +++ b/include/linux/virtio.h
> @@ -10,6 +10,7 @@
> #include <linux/mod_devicetable.h>
> #include <linux/gfp.h>
> #include <linux/dma-mapping.h>
> +#include <linux/completion.h>
>
> /**
> * struct virtqueue - a queue to register buffers for sending or receiving.
> @@ -109,6 +110,7 @@ struct virtio_admin_cmd {
> __le64 group_member_id;
> struct scatterlist *data_sg;
> struct scatterlist *result_sg;
> + struct completion completion;
> };
>
> /**
> --
> 2.45.1
