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

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

On Mon, Oct 30, 2023 at 05:27:50PM +0200, Yishai Hadas wrote:
> On 29/10/2023 22:17, Michael S. Tsirkin wrote:
> > 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.
> 
> OK, will be part of V3.
> 
> > 
> > >   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 */
> 
> I assume that you asked for adding the below comment before the while loop:
> /* TODO use interrupts to reduce cpu cycles in the future */
> 
> Right ?
> 
> Yishai

Well I wrote what I meant. in the future is redundant - everyone knows
we can't change the past.

> > 
> > >   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
> 

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