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

Jason Wang <jasowang@xxxxxxxxxx> · Tue, 10 Nov 2020 10:44:45 +0800

On 2020/11/10 上午2:41, Mike Christie wrote:
On 11/8/20 10:01 PM, Jason Wang wrote:

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 

We can do this code wise, but I was not sure about the spec and 
VHOST_SET_OWNER's requirements. For the latter, the first ioctl cmd 
quemu does is VHOST_SET_OWNER. The vhost_dev_ioctl then requires that 
the caller be the owner to be able to do any other ioctls. The 
individual drivers like scsi, net, etc allow userspace to do ioctls 
without being the owner, and I was not sure if that is by accident or 
design.


My understanding is that owner is required for memory mapping 
operations. For setting #max_vqs, net will talk with the backend 
(TUN/TAP) instead of vhost. For SCSI, it looks OK to do it without an 
owner (my understanding is that vhost-scsi doesn't need to tell #max_vqs 
to the under-layer).



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 

If it's allowed to do ioctl cmds that set vhost driver settings before 
VHOST_SET_OWNER then we can do the VRING_ENABLE calls first. For that 
though, I had one question about the spec. In section "4.1.4.3.2 
Driver Requirements: Common configuration structure layout" it had the 
line:

-----
The driver MUST configure the other virtqueue fields before enabling 
the virtqueue with queue_enable.
-----

Does that apply to our case, or only when it's being used in a 
virtio_pci_common_cfg struct based command? 


The spec is for virtio(pci) only, for vhost, it could choose to follow 
the spec (which should be better) or not.


If it applies to our case, then we have to change userspace to set 
config settings like the queue_size and features earlier, right?


Yes, or do VRING_ENABLE after queue_size and features are set.



I was thinking if we had to deal with that then maybe it's better to 
add a new ioctl like VRING_CREATE. It would be done first, singles 
that the kernel should do the vq creation (allocation, init steps we 
do in vhost_dev_init, etc).


Technically, that's possible, but it looks like a new version of vhost 
ioctl protocol which requires new features to be advertised to userspace 
to choose between the two. I'm not sure it's worth to do that.



vhost-scsi, for 0.9x device qemu can simply check whether ring.addr 
is zero or not
I had a question about that and my thread per vq patches.

If you want to pair this patchset down to it's bare bug fixes that 
prevent users from getting IO errors, I would do ring.addr check only 
approach for this bug fix patchset.


Yes, I think it would be helpful if we can limit the changes to bug fixes.



For my other patchset to do a vhost worker thread per vq, I think it 
would be cleanest to have a new ioctl or a userspace change. The 
problem is that we create the worker thread in vhost_dev_set_owner and 
at that time we do not know how many vqs there are going to be. For 
that we could:
1. Add a new VHOST_SET_OWNER_V2 that has an arg which contains the 
number of queues or worker threads
2. do the VRING_ENABLE approach if allowed spec/VHOST_SET_OWNER wise.
3. add a new ioctl that is done before VHOST_SET_OWNER


Can we just create one worker during SET_OWNER and for the rest during 
VRING_ENABLE?



If we split it up like this, current users get the IO error bug fixes. 
This patchset gets a lot smaller. Users would then only have to 
upgrade userspace to get the multple thread feature.


Yes.



Compat setup support might be cleaner too. If we did the 
VHOST_SET_OWNER_V2 or added a new ioctl then vhost_dev_set_owner just 
takes the new arg and loops num_queues/workers times to create more 
threads.



Thanks


- 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;



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