Re: [PATCH V2 vfio 5/9] virtio-pci: Initialize the supported admin commands

["Michael S. Tsirkin" <mst@redhat.com>]

On Sun, Oct 29, 2023 at 05:59:48PM +0200, Yishai Hadas wrote:
> Initialize the supported admin commands upon activating the admin queue.
> 
> The supported commands are saved as part of the admin queue context, it
> will be used by the next patches from this series.
> 
> Note:
> As we don't want to let upper layers to execute admin commands before
> that this initialization step was completed, we set ref count to 1 only
> post of that flow and use a non ref counted version command for this
> internal flow.
> 
> Signed-off-by: Yishai Hadas <yishaih@nvidia.com>
> ---
>  drivers/virtio/virtio_pci_common.h |  1 +
>  drivers/virtio/virtio_pci_modern.c | 77 +++++++++++++++++++++++++++++-
>  2 files changed, 77 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/virtio/virtio_pci_common.h b/drivers/virtio/virtio_pci_common.h
> index a21b9ba01a60..9e07e556a51a 100644
> --- a/drivers/virtio/virtio_pci_common.h
> +++ b/drivers/virtio/virtio_pci_common.h
> @@ -46,6 +46,7 @@ struct virtio_pci_admin_vq {
>  	struct virtio_pci_vq_info info;
>  	struct completion flush_done;
>  	refcount_t refcount;
> +	u64 supported_cmds;
>  	/* Name of the admin queue: avq.$index. */
>  	char name[10];
>  	u16 vq_index;
> diff --git a/drivers/virtio/virtio_pci_modern.c b/drivers/virtio/virtio_pci_modern.c
> index ccd7a4d9f57f..25e27aa79cab 100644
> --- a/drivers/virtio/virtio_pci_modern.c
> +++ b/drivers/virtio/virtio_pci_modern.c
> @@ -19,6 +19,9 @@
>  #define VIRTIO_RING_NO_LEGACY
>  #include "virtio_pci_common.h"
>  
> +static int vp_modern_admin_cmd_exec(struct virtio_device *vdev,
> +				    struct virtio_admin_cmd *cmd);
> +

I don't much like forward declarations. Just order functions sensibly
and they will not be needed.

>  static u64 vp_get_features(struct virtio_device *vdev)
>  {
>  	struct virtio_pci_device *vp_dev = to_vp_device(vdev);
> @@ -59,6 +62,42 @@ vp_modern_avq_set_abort(struct virtio_pci_admin_vq *admin_vq, bool abort)
>  	WRITE_ONCE(admin_vq->abort, abort);
>  }
>  
> +static void virtio_pci_admin_init_cmd_list(struct virtio_device *virtio_dev)
> +{
> +	struct virtio_pci_device *vp_dev = to_vp_device(virtio_dev);
> +	struct virtio_admin_cmd cmd = {};
> +	struct scatterlist result_sg;
> +	struct scatterlist data_sg;
> +	__le64 *data;
> +	int ret;
> +
> +	data = kzalloc(sizeof(*data), GFP_KERNEL);
> +	if (!data)
> +		return;
> +
> +	sg_init_one(&result_sg, data, sizeof(*data));
> +	cmd.opcode = cpu_to_le16(VIRTIO_ADMIN_CMD_LIST_QUERY);
> +	cmd.group_type = cpu_to_le16(VIRTIO_ADMIN_GROUP_TYPE_SRIOV);
> +	cmd.result_sg = &result_sg;
> +
> +	ret = vp_modern_admin_cmd_exec(virtio_dev, &cmd);
> +	if (ret)
> +		goto end;
> +
> +	sg_init_one(&data_sg, data, sizeof(*data));
> +	cmd.opcode = cpu_to_le16(VIRTIO_ADMIN_CMD_LIST_USE);
> +	cmd.data_sg = &data_sg;
> +	cmd.result_sg = NULL;
> +
> +	ret = vp_modern_admin_cmd_exec(virtio_dev, &cmd);
> +	if (ret)
> +		goto end;
> +
> +	vp_dev->admin_vq.supported_cmds = le64_to_cpu(*data);
> +end:
> +	kfree(data);
> +}
> +
>  static void vp_modern_avq_activate(struct virtio_device *vdev)
>  {
>  	struct virtio_pci_device *vp_dev = to_vp_device(vdev);
> @@ -67,6 +106,7 @@ static void vp_modern_avq_activate(struct virtio_device *vdev)
>  	if (!virtio_has_feature(vdev, VIRTIO_F_ADMIN_VQ))
>  		return;
>  
> +	virtio_pci_admin_init_cmd_list(vdev);
>  	init_completion(&admin_vq->flush_done);
>  	refcount_set(&admin_vq->refcount, 1);
>  	vp_modern_avq_set_abort(admin_vq, false);
> @@ -562,6 +602,35 @@ static bool vp_get_shm_region(struct virtio_device *vdev,
>  	return true;
>  }
>  
> +static int __virtqueue_exec_admin_cmd(struct virtio_pci_admin_vq *admin_vq,
> +				    struct scatterlist **sgs,
> +				    unsigned int out_num,
> +				    unsigned int in_num,
> +				    void *data,
> +				    gfp_t gfp)
> +{
> +	struct virtqueue *vq;
> +	int ret, len;
> +
> +	vq = admin_vq->info.vq;
> +
> +	ret = virtqueue_add_sgs(vq, sgs, out_num, in_num, data, gfp);
> +	if (ret < 0)
> +		return ret;
> +
> +	if (unlikely(!virtqueue_kick(vq)))
> +		return -EIO;
> +
> +	while (!virtqueue_get_buf(vq, &len) &&
> +	       !virtqueue_is_broken(vq))
> +		cpu_relax();
> +
> +	if (virtqueue_is_broken(vq))
> +		return -EIO;
> +
> +	return 0;
> +}
> +


This is tolerable I guess but it might pin the CPU for a long time.
The difficulty is handling suprize removal well which we currently
don't do with interrupts. I would say it's ok as is but add
a TODO comments along the lines of /* TODO: use interrupts once these virtqueue_is_broken */

>  static int virtqueue_exec_admin_cmd(struct virtio_pci_admin_vq *admin_vq,
>  				    struct scatterlist **sgs,
>  				    unsigned int out_num,
> @@ -653,7 +722,13 @@ static int vp_modern_admin_cmd_exec(struct virtio_device *vdev,
>  		in_num++;
>  	}
>  
> -	ret = virtqueue_exec_admin_cmd(&vp_dev->admin_vq, sgs,
> +	if (cmd->opcode == VIRTIO_ADMIN_CMD_LIST_QUERY ||
> +	    cmd->opcode == VIRTIO_ADMIN_CMD_LIST_USE)
> +		ret = __virtqueue_exec_admin_cmd(&vp_dev->admin_vq, sgs,
> +				       out_num, in_num,
> +				       sgs, GFP_KERNEL);
> +	else
> +		ret = virtqueue_exec_admin_cmd(&vp_dev->admin_vq, sgs,
>  				       out_num, in_num,
>  				       sgs, GFP_KERNEL);
>  	if (ret) {
> -- 
> 2.27.0