Re: [PATCH 06/11] vhost: support delayed vq creation

[Jason Wang <jasowang@xxxxxxxxxx>]

On 2020/11/5 上午6:26, Mike Christie wrote:
> This allows vq creation to be done when it's first accessed by
> userspace. vhost-scsi doesn't know how many queues the user requested
> until they are first setup, and we don't want to allocate resources
> like the iovecs for 128 vqs when we are only using 1 or 2 most of the
> time. In the next pathces, vhost-scsi will also switch to preallocating
> cmds per vq instead of per lio session and we don't want to allocate
> them for 127 extra vqs if they are not in use.
>
> With this patch when a driver calls vhost_dev_init they pass in the
> number of vqs that they know they need and the max they can support.
> This patch has all the drivers pass in the same value for both the
> initial number of vqs and the max. The next patch will convert scsi.
> The other drivers like net/vsock have their vqs hard coded in the
> kernel or setup/discovered via other methods like with vdpa.
>
> Signed-off-by: Mike Christie <michael.christie@xxxxxxxxxx>


This looks like a delayed vq metadata creation instead of vq itself.

Several questions:

- can we simply introduce new ioctls to set the #max_vqs for SCSI? Or 
simply introduce VRING_ENABLE ioctl for SCSI and let qemu to call that 
ioctl for 1.0 device, qemu can simply forward the ENABLE command to 
vhost-scsi, for 0.9x device qemu can simply check whether ring.addr is 
zero or not?
- if not, it's better to convert all the devices/queues to behave as if 
SCSI to have a consistent way allocate metadata
- do we need to care about vq free, e.g free vqs during reset?

Thanks


> ---
>   drivers/vhost/net.c   |  2 +-
>   drivers/vhost/scsi.c  |  4 +--
>   drivers/vhost/test.c  |  5 ++--
>   drivers/vhost/vdpa.c  |  2 +-
>   drivers/vhost/vhost.c | 71 ++++++++++++++++++++++++++++++++++-----------------
>   drivers/vhost/vhost.h |  7 +++--
>   drivers/vhost/vsock.c | 11 ++++----
>   7 files changed, 66 insertions(+), 36 deletions(-)
>
> diff --git a/drivers/vhost/net.c b/drivers/vhost/net.c
> index fd30b53..fce46f0 100644
> --- a/drivers/vhost/net.c
> +++ b/drivers/vhost/net.c
> @@ -1316,7 +1316,7 @@ static int vhost_net_open(struct inode *inode, struct file *f)
>   		n->vqs[i].rx_ring = NULL;
>   		vhost_net_buf_init(&n->vqs[i].rxq);
>   	}
> -	if (vhost_dev_init(dev, vqs, VHOST_NET_VQ_MAX,
> +	if (vhost_dev_init(dev, vqs, VHOST_NET_VQ_MAX, VHOST_NET_VQ_MAX,
>   			   UIO_MAXIOV + VHOST_NET_BATCH,
>   			   VHOST_NET_PKT_WEIGHT, VHOST_NET_WEIGHT, true,
>   			   NULL))
> diff --git a/drivers/vhost/scsi.c b/drivers/vhost/scsi.c
> index ed8baf9..5b3720e 100644
> --- a/drivers/vhost/scsi.c
> +++ b/drivers/vhost/scsi.c
> @@ -1632,8 +1632,8 @@ static int vhost_scsi_open(struct inode *inode, struct file *f)
>   		vqs[i] = &vs->vqs[i].vq;
>   		vs->vqs[i].vq.handle_kick = vhost_scsi_handle_kick;
>   	}
> -	r = vhost_dev_init(&vs->dev, vqs, VHOST_SCSI_MAX_VQ, UIO_MAXIOV,
> -			   VHOST_SCSI_WEIGHT, 0, true, NULL);
> +	r = vhost_dev_init(&vs->dev, vqs, VHOST_SCSI_MAX_VQ, VHOST_SCSI_MAX_VQ,
> +			   UIO_MAXIOV, VHOST_SCSI_WEIGHT, 0, true, NULL);
>   	if (r)
>   		goto err_dev_init;
>   
> diff --git a/drivers/vhost/test.c b/drivers/vhost/test.c
> index c255ae5..9d2bfa3 100644
> --- a/drivers/vhost/test.c
> +++ b/drivers/vhost/test.c
> @@ -119,8 +119,9 @@ static int vhost_test_open(struct inode *inode, struct file *f)
>   	dev = &n->dev;
>   	vqs[VHOST_TEST_VQ] = &n->vqs[VHOST_TEST_VQ];
>   	n->vqs[VHOST_TEST_VQ].handle_kick = handle_vq_kick;
> -	if (vhost_dev_init(dev, vqs, VHOST_TEST_VQ_MAX, UIO_MAXIOV,
> -			   VHOST_TEST_PKT_WEIGHT, VHOST_TEST_WEIGHT, true, NULL)
> +	if (vhost_dev_init(dev, vqs, VHOST_TEST_VQ_MAX, VHOST_TEST_VQ_MAX,
> +			   UIO_MAXIOV, VHOST_TEST_PKT_WEIGHT, VHOST_TEST_WEIGHT,
> +			   true, NULL)
>   		goto err_dev_init;
>   
>   	f->private_data = n;
> diff --git a/drivers/vhost/vdpa.c b/drivers/vhost/vdpa.c
> index c1615a7..6abd9d8 100644
> --- a/drivers/vhost/vdpa.c
> +++ b/drivers/vhost/vdpa.c
> @@ -829,7 +829,7 @@ static int vhost_vdpa_open(struct inode *inode, struct file *filep)
>   		vqs[i] = &v->vqs[i];
>   		vqs[i]->handle_kick = handle_vq_kick;
>   	}
> -	r = vhost_dev_init(dev, vqs, nvqs, 0, 0, 0, false,
> +	r = vhost_dev_init(dev, vqs, nvqs, nvqs, 0, 0, 0, false,
>   			   vhost_vdpa_process_iotlb_msg);
>   	if (r)
>   		goto err_dev_init;
> diff --git a/drivers/vhost/vhost.c b/drivers/vhost/vhost.c
> index a4a4450..2ca2e71 100644
> --- a/drivers/vhost/vhost.c
> +++ b/drivers/vhost/vhost.c
> @@ -294,7 +294,7 @@ static void vhost_vq_meta_reset(struct vhost_dev *d)
>   {
>   	int i;
>   
> -	for (i = 0; i < d->nvqs; ++i)
> +	for (i = 0; i < d->max_nvqs; ++i)
>   		__vhost_vq_meta_reset(d->vqs[i]);
>   }
>   
> @@ -331,6 +331,7 @@ static void vhost_vq_reset(struct vhost_dev *dev,
>   	vq->busyloop_timeout = 0;
>   	vq->umem = NULL;
>   	vq->iotlb = NULL;
> +	vq->initialized = false;
>   	vhost_vring_call_reset(&vq->call_ctx);
>   	__vhost_vq_meta_reset(vq);
>   }
> @@ -411,7 +412,7 @@ static void vhost_dev_free_iovecs(struct vhost_dev *dev)
>   {
>   	int i;
>   
> -	for (i = 0; i < dev->nvqs; ++i)
> +	for (i = 0; i < dev->max_nvqs; ++i)
>   		vhost_vq_free_iovecs(dev->vqs[i]);
>   }
>   
> @@ -456,7 +457,7 @@ static size_t vhost_get_desc_size(struct vhost_virtqueue *vq,
>   	return sizeof(*vq->desc) * num;
>   }
>   
> -static int vhost_vq_init(struct vhost_dev *dev, struct vhost_virtqueue *vq)
> +static void __vhost_vq_init(struct vhost_dev *dev, struct vhost_virtqueue *vq)
>   {
>   	vq->log = NULL;
>   	vq->indirect = NULL;
> @@ -467,12 +468,29 @@ static int vhost_vq_init(struct vhost_dev *dev, struct vhost_virtqueue *vq)
>   
>   	if (vq->handle_kick)
>   		vhost_poll_init(&vq->poll, vq->handle_kick, EPOLLIN, dev);
> +}
> +
> +static int vhost_vq_init(struct vhost_dev *dev, int vq_idx)
> +{
> +	struct vhost_virtqueue *vq;
> +	int ret;
> +
> +	if (vq_idx >= dev->max_nvqs)
> +		return -ENOBUFS;
> +
> +	vq = dev->vqs[vq_idx];
> +	__vhost_vq_init(dev, vq);
> +	ret = vhost_vq_alloc_iovecs(dev, vq);
> +	if (ret)
> +		return ret;
>   
> -	return vhost_vq_alloc_iovecs(dev, vq);
> +	vq->initialized = true;
> +	dev->nvqs++;
> +	return 0;
>   }
>   
>   int vhost_dev_init(struct vhost_dev *dev,
> -		   struct vhost_virtqueue **vqs, int nvqs,
> +		   struct vhost_virtqueue **vqs, int nvqs, int max_nvqs,
>   		   int iov_limit, int weight, int byte_weight,
>   		   bool use_worker,
>   		   int (*msg_handler)(struct vhost_dev *dev,
> @@ -481,7 +499,8 @@ int vhost_dev_init(struct vhost_dev *dev,
>   	int i;
>   
>   	dev->vqs = vqs;
> -	dev->nvqs = nvqs;
> +	dev->nvqs = 0;
> +	dev->max_nvqs = max_nvqs;
>   	mutex_init(&dev->mutex);
>   	dev->log_ctx = NULL;
>   	dev->umem = NULL;
> @@ -499,12 +518,15 @@ int vhost_dev_init(struct vhost_dev *dev,
>   	INIT_LIST_HEAD(&dev->pending_list);
>   	spin_lock_init(&dev->iotlb_lock);
>   
> -
> -	for (i = 0; i < dev->nvqs; ++i) {
> -		if (vhost_vq_init(dev, dev->vqs[i]))
> +	for (i = 0; i < nvqs; ++i) {
> +		if (vhost_vq_init(dev, i))
>   			goto err_vq_init;
>   	}
>   
> +	for (; i < dev->max_nvqs; ++i)
> +		/* Just prep/clear the fields and set initialized=false */
> +		__vhost_vq_init(dev, dev->vqs[i]);
> +
>   	return 0;
>   
>   err_vq_init:
> @@ -652,7 +674,7 @@ void vhost_dev_reset_owner(struct vhost_dev *dev, struct vhost_iotlb *umem)
>   	/* We don't need VQ locks below since vhost_dev_cleanup makes sure
>   	 * VQs aren't running.
>   	 */
> -	for (i = 0; i < dev->nvqs; ++i)
> +	for (i = 0; i < dev->max_nvqs; ++i)
>   		dev->vqs[i]->umem = umem;
>   }
>   EXPORT_SYMBOL_GPL(vhost_dev_reset_owner);
> @@ -661,7 +683,7 @@ void vhost_dev_stop(struct vhost_dev *dev)
>   {
>   	int i;
>   
> -	for (i = 0; i < dev->nvqs; ++i) {
> +	for (i = 0; i < dev->max_nvqs; ++i) {
>   		if (dev->vqs[i]->kick && dev->vqs[i]->handle_kick) {
>   			vhost_poll_stop(&dev->vqs[i]->poll);
>   			vhost_poll_flush(&dev->vqs[i]->poll);
> @@ -693,7 +715,7 @@ void vhost_dev_cleanup(struct vhost_dev *dev)
>   {
>   	int i;
>   
> -	for (i = 0; i < dev->nvqs; ++i) {
> +	for (i = 0; i < dev->max_nvqs; ++i) {
>   		if (dev->vqs[i]->error_ctx)
>   			eventfd_ctx_put(dev->vqs[i]->error_ctx);
>   		if (dev->vqs[i]->kick)
> @@ -787,7 +809,7 @@ static bool memory_access_ok(struct vhost_dev *d, struct vhost_iotlb *umem,
>   {
>   	int i;
>   
> -	for (i = 0; i < d->nvqs; ++i) {
> +	for (i = 0; i < d->max_nvqs; ++i) {
>   		bool ok;
>   		bool log;
>   
> @@ -999,14 +1021,14 @@ static inline int vhost_put_used_idx(struct vhost_virtqueue *vq)
>   static void vhost_dev_lock_vqs(struct vhost_dev *d)
>   {
>   	int i = 0;
> -	for (i = 0; i < d->nvqs; ++i)
> +	for (i = 0; i < d->max_nvqs; ++i)
>   		mutex_lock_nested(&d->vqs[i]->mutex, i);
>   }
>   
>   static void vhost_dev_unlock_vqs(struct vhost_dev *d)
>   {
>   	int i = 0;
> -	for (i = 0; i < d->nvqs; ++i)
> +	for (i = 0; i < d->max_nvqs; ++i)
>   		mutex_unlock(&d->vqs[i]->mutex);
>   }
>   
> @@ -1462,7 +1484,7 @@ static long vhost_set_memory(struct vhost_dev *d, struct vhost_memory __user *m)
>   	d->umem = newumem;
>   
>   	/* All memory accesses are done under some VQ mutex. */
> -	for (i = 0; i < d->nvqs; ++i) {
> +	for (i = 0; i < d->max_nvqs; ++i) {
>   		mutex_lock(&d->vqs[i]->mutex);
>   		d->vqs[i]->umem = newumem;
>   		mutex_unlock(&d->vqs[i]->mutex);
> @@ -1590,11 +1612,14 @@ long vhost_vring_ioctl(struct vhost_dev *d, unsigned int ioctl, void __user *arg
>   	r = get_user(idx, idxp);
>   	if (r < 0)
>   		return r;
> -	if (idx >= d->nvqs)
> -		return -ENOBUFS;
>   
> -	idx = array_index_nospec(idx, d->nvqs);
> +	idx = array_index_nospec(idx, d->max_nvqs);
>   	vq = d->vqs[idx];
> +	if (!vq->initialized) {
> +		r = vhost_vq_init(d, idx);
> +		if (r)
> +			return r;
> +	}
>   
>   	if (ioctl == VHOST_SET_VRING_NUM ||
>   	    ioctl == VHOST_SET_VRING_ADDR) {
> @@ -1724,7 +1749,7 @@ int vhost_init_device_iotlb(struct vhost_dev *d, bool enabled)
>   	oiotlb = d->iotlb;
>   	d->iotlb = niotlb;
>   
> -	for (i = 0; i < d->nvqs; ++i) {
> +	for (i = 0; i < d->max_nvqs; ++i) {
>   		struct vhost_virtqueue *vq = d->vqs[i];
>   
>   		mutex_lock(&vq->mutex);
> @@ -1771,7 +1796,7 @@ long vhost_dev_ioctl(struct vhost_dev *d, unsigned int ioctl, void __user *argp)
>   			r = -EFAULT;
>   			break;
>   		}
> -		for (i = 0; i < d->nvqs; ++i) {
> +		for (i = 0; i < d->max_nvqs; ++i) {
>   			struct vhost_virtqueue *vq;
>   			void __user *base = (void __user *)(unsigned long)p;
>   			vq = d->vqs[i];
> @@ -1794,7 +1819,7 @@ long vhost_dev_ioctl(struct vhost_dev *d, unsigned int ioctl, void __user *argp)
>   			break;
>   		}
>   		swap(ctx, d->log_ctx);
> -		for (i = 0; i < d->nvqs; ++i) {
> +		for (i = 0; i < d->max_nvqs; ++i) {
>   			mutex_lock(&d->vqs[i]->mutex);
>   			d->vqs[i]->log_ctx = d->log_ctx;
>   			mutex_unlock(&d->vqs[i]->mutex);
> @@ -2609,7 +2634,7 @@ void vhost_set_backend_features(struct vhost_dev *dev, u64 features)
>   	int i;
>   
>   	mutex_lock(&dev->mutex);
> -	for (i = 0; i < dev->nvqs; ++i) {
> +	for (i = 0; i < dev->max_nvqs; ++i) {
>   		vq = dev->vqs[i];
>   		mutex_lock(&vq->mutex);
>   		vq->acked_backend_features = features;
> diff --git a/drivers/vhost/vhost.h b/drivers/vhost/vhost.h
> index 9ad34b1..9677870 100644
> --- a/drivers/vhost/vhost.h
> +++ b/drivers/vhost/vhost.h
> @@ -132,6 +132,8 @@ struct vhost_virtqueue {
>   	bool user_be;
>   #endif
>   	u32 busyloop_timeout;
> +
> +	bool initialized;
>   };
>   
>   struct vhost_msg_node {
> @@ -148,6 +150,7 @@ struct vhost_dev {
>   	struct mutex mutex;
>   	struct vhost_virtqueue **vqs;
>   	int nvqs;
> +	int max_nvqs;
>   	struct eventfd_ctx *log_ctx;
>   	struct llist_head work_list;
>   	struct task_struct *worker;
> @@ -168,8 +171,8 @@ struct vhost_dev {
>   
>   bool vhost_exceeds_weight(struct vhost_virtqueue *vq, int pkts, int total_len);
>   int vhost_dev_init(struct vhost_dev *dev, struct vhost_virtqueue **vqs,
> -		   int nvqs, int iov_limit, int weight, int byte_weight,
> -		   bool use_worker,
> +		   int nvqs, int max_nvqs, int iov_limit, int weight,
> +		   int byte_weight, bool use_worker,
>   		   int (*msg_handler)(struct vhost_dev *dev,
>   				      struct vhost_iotlb_msg *msg));
>   long vhost_dev_set_owner(struct vhost_dev *dev);
> diff --git a/drivers/vhost/vsock.c b/drivers/vhost/vsock.c
> index cae0083..bcdfd58 100644
> --- a/drivers/vhost/vsock.c
> +++ b/drivers/vhost/vsock.c
> @@ -606,7 +606,7 @@ static int vhost_vsock_dev_open(struct inode *inode, struct file *file)
>   {
>   	struct vhost_virtqueue **vqs;
>   	struct vhost_vsock *vsock;
> -	int ret;
> +	int ret, nvqs;
>   
>   	/* This struct is large and allocation could fail, fall back to vmalloc
>   	 * if there is no other way.
> @@ -615,7 +615,8 @@ static int vhost_vsock_dev_open(struct inode *inode, struct file *file)
>   	if (!vsock)
>   		return -ENOMEM;
>   
> -	vqs = kmalloc_array(ARRAY_SIZE(vsock->vqs), sizeof(*vqs), GFP_KERNEL);
> +	nvqs = ARRAY_SIZE(vsock->vqs);
> +	vqs = kmalloc_array(nvqs, sizeof(*vqs), GFP_KERNEL);
>   	if (!vqs) {
>   		ret = -ENOMEM;
>   		goto out;
> @@ -630,9 +631,9 @@ static int vhost_vsock_dev_open(struct inode *inode, struct file *file)
>   	vsock->vqs[VSOCK_VQ_TX].handle_kick = vhost_vsock_handle_tx_kick;
>   	vsock->vqs[VSOCK_VQ_RX].handle_kick = vhost_vsock_handle_rx_kick;
>   
> -	ret = vhost_dev_init(&vsock->dev, vqs, ARRAY_SIZE(vsock->vqs),
> -			     UIO_MAXIOV, VHOST_VSOCK_PKT_WEIGHT,
> -			     VHOST_VSOCK_WEIGHT, true, NULL);
> +	ret = vhost_dev_init(&vsock->dev, vqs, nvqs, nvqs, UIO_MAXIOV,
> +			     VHOST_VSOCK_PKT_WEIGHT, VHOST_VSOCK_WEIGHT, true,
> +			     NULL);
>   	if (ret)
>   		goto err_dev_init;
>