Re: [PATCH RESENT v4 4/6] vdpa: validate device feature provisioning against supported class

[Si-Wei Liu]

Hi Eugenio,

On 10/1/2025 6:26 AM, Eugenio Perez Martin wrote:
On Tue, Feb 7, 2023 at 12:15 AM Si-Wei Liu <si-wei....@oracle.com> wrote:
Today when device features are explicitly provisioned, the features
user supplied may contain device class specific features that are
not supported by the parent management device. On the other hand,
when parent management device supports more than one class, the
device features to provision may be ambiguous if none of the class
specific attributes is provided at the same time. Validate these
cases and prompt appropriate user errors accordingly.
Signed-off-by: Si-Wei Liu <si-wei....@oracle.com>
---
  drivers/vdpa/vdpa.c | 59 +++++++++++++++++++++++++++++++++++++++++++++--------
  1 file changed, 50 insertions(+), 9 deletions(-)

diff --git a/drivers/vdpa/vdpa.c b/drivers/vdpa/vdpa.c
index 1eba978..8da5120 100644
--- a/drivers/vdpa/vdpa.c
+++ b/drivers/vdpa/vdpa.c
@@ -460,12 +460,28 @@ static int vdpa_nl_mgmtdev_handle_fill(struct sk_buff 
*msg, const struct vdpa_mg
         return 0;
  }

+static u64 vdpa_mgmtdev_get_classes(const struct vdpa_mgmt_dev *mdev,
+                                   unsigned int *nclasses)
+{
+       u64 supported_classes = 0;
+       unsigned int n = 0;
+
+       for (int i = 0; mdev->id_table[i].device; i++) {
+               if (mdev->id_table[i].device > 63)
+                       continue;
+               supported_classes |= BIT_ULL(mdev->id_table[i].device);
+               n++;
+       }
+       if (nclasses)
+               *nclasses = n;
+
+       return supported_classes;
+}
+
  static int vdpa_mgmtdev_fill(const struct vdpa_mgmt_dev *mdev, struct sk_buff 
*msg,
                              u32 portid, u32 seq, int flags)
  {
-       u64 supported_classes = 0;
         void *hdr;
-       int i = 0;
         int err;

         hdr = genlmsg_put(msg, portid, seq, &vdpa_nl_family, flags, 
VDPA_CMD_MGMTDEV_NEW);
@@ -475,14 +491,9 @@ static int vdpa_mgmtdev_fill(const struct vdpa_mgmt_dev 
*mdev, struct sk_buff *m
         if (err)
                 goto msg_err;

-       while (mdev->id_table[i].device) {
-               if (mdev->id_table[i].device <= 63)
-                       supported_classes |= BIT_ULL(mdev->id_table[i].device);
-               i++;
-       }
-
         if (nla_put_u64_64bit(msg, VDPA_ATTR_MGMTDEV_SUPPORTED_CLASSES,
-                             supported_classes, VDPA_ATTR_UNSPEC)) {
+                             vdpa_mgmtdev_get_classes(mdev, NULL),
+                             VDPA_ATTR_UNSPEC)) {
                 err = -EMSGSIZE;
                 goto msg_err;
         }
@@ -566,13 +577,25 @@ static int vdpa_nl_cmd_mgmtdev_get_doit(struct sk_buff 
*skb, struct genl_info *i
                                  BIT_ULL(VDPA_ATTR_DEV_NET_CFG_MTU)     | \
                                  BIT_ULL(VDPA_ATTR_DEV_NET_CFG_MAX_VQP))

+/*
+ * Bitmask for all per-device features: feature bits VIRTIO_TRANSPORT_F_START
+ * through VIRTIO_TRANSPORT_F_END are unset, i.e. 0xfffffc000fffffff for
+ * all 64bit features. If the features are extended beyond 64 bits, or new
+ * "holes" are reserved for other type of features than per-device, this
+ * macro would have to be updated.
+ */
+#define VIRTIO_DEVICE_F_MASK (~0ULL << (VIRTIO_TRANSPORT_F_END + 1) | \
+                             ((1ULL << VIRTIO_TRANSPORT_F_START) - 1))
+
  static int vdpa_nl_cmd_dev_add_set_doit(struct sk_buff *skb, struct genl_info 
*info)
  {
         struct vdpa_dev_set_config config = {};
         struct nlattr **nl_attrs = info->attrs;
         struct vdpa_mgmt_dev *mdev;
+       unsigned int ncls = 0;
         const u8 *macaddr;
         const char *name;
+       u64 classes;
         int err = 0;

         if (!info->attrs[VDPA_ATTR_DEV_NAME])
@@ -649,6 +672,24 @@ static int vdpa_nl_cmd_dev_add_set_doit(struct sk_buff 
*skb, struct genl_info *i
                 goto err;
         }

+       classes = vdpa_mgmtdev_get_classes(mdev, &ncls);
+       if (config.mask & VDPA_DEV_NET_ATTRS_MASK &&
+           !(classes & BIT_ULL(VIRTIO_ID_NET))) {
+               NL_SET_ERR_MSG_MOD(info->extack,
+                                  "Network class attributes provided on unsupported 
management device");
+               err = -EINVAL;
+               goto err;
+       }
+       if (!(config.mask & VDPA_DEV_NET_ATTRS_MASK) &&
+           config.mask & BIT_ULL(VDPA_ATTR_DEV_FEATURES) &&
+           classes & BIT_ULL(VIRTIO_ID_NET) && ncls > 1 &&
+           config.device_features & VIRTIO_DEVICE_F_MASK) {
+               NL_SET_ERR_MSG_MOD(info->extack,
+                                  "Management device supports multi-class while 
device features specified are ambiguous");
+               err = -EINVAL;
+               goto err;
+       }

Hi! I need to question this last if() :). What's the point of error
when we specify features device-specific, from net or blk?
Because device specific features belong to different feature space, for 
instance, VIRTIO_BLK_F_SIZE_MAX (1) on block device and 
VIRTIO_NET_F_GUEST_CSUM (1) on network device both use same feature bit 
value of (1<<1)ULL, but they belong to different type of devices.


In the VDUSE case both blk and net are supported. I want to use
device_features to limit the net features that the VDUSE device
exports.
Then we have to extend to the vdpa CLI to add "class ..." attribute to 
explicitly indicate which type of device the creation has to be, so 
eliminate the ambiguity entirely.


Also, why is this limited to only net devices?
Actually, this is not limited to only net I think, we can even remove the

classes & BIT_ULL(VIRTIO_ID_NET)

conditional if mgmtdev and vdpa dev instance is 1:1 bound. But at the 
point when this code was written, it's not clear to me how multi-class 
can be supported - such that does it limit to one vdpa instance 
supporting one single class 1:1, or it is even possible to support both 
or multiple classes (multi-facets) per vdpa instance i.e. 1:N.

  does this part:

classes & BIT_ULL(VIRTIO_ID_NET) && ncls > 1

Means that it is ok to specify more than one class as long as the set
does not contain net?
Exactly, that's why it is coded in that odd way. For instance, if a 
multi-facet vdpa instance needs to be provisioned with respective 
feature bits for both block and iSCSI device types at the same time, we 
may have to extend the CLI usage to support that.

Thanks,
-Siwei


+
         err = mdev->ops->dev_add(mdev, name, &config);
  err:
         up_write(&vdpa_dev_lock);
--
1.8.3.1