[RFC] vdpa/mlx5: preserve CVQ vringh index

[Steve Sistare <steven.sistare@oracle.com>]

mlx5_vdpa does not preserve userland's view of vring base for the control
queue in the following sequence:

ioctl VHOST_SET_VRING_BASE
ioctl VHOST_VDPA_SET_STATUS VIRTIO_CONFIG_S_DRIVER_OK
  mlx5_vdpa_set_status()
    setup_cvq_vring()
      vringh_init_iotlb()
        vringh_init_kern()
          vrh->last_avail_idx = 0;
ioctl VHOST_GET_VRING_BASE

To fix, restore the value of cvq->vring.last_avail_idx after calling
vringh_init_iotlb.

Signed-off-by: Steve Sistare <steven.sistare@oracle.com>
---
 drivers/vdpa/mlx5/net/mlx5_vnet.c |  7 ++++++-
 drivers/vhost/vringh.c            | 30 ++++++++++++++++++++++++++++++
 include/linux/vringh.h            |  2 ++
 3 files changed, 38 insertions(+), 1 deletion(-)

diff --git a/drivers/vdpa/mlx5/net/mlx5_vnet.c b/drivers/vdpa/mlx5/net/mlx5_vnet.c
index 946488b8989f..f64758143115 100644
--- a/drivers/vdpa/mlx5/net/mlx5_vnet.c
+++ b/drivers/vdpa/mlx5/net/mlx5_vnet.c
@@ -2795,13 +2795,18 @@ static int setup_cvq_vring(struct mlx5_vdpa_dev *mvdev)
 	struct mlx5_control_vq *cvq = &mvdev->cvq;
 	int err = 0;
 
-	if (mvdev->actual_features & BIT_ULL(VIRTIO_NET_F_CTRL_VQ))
+	if (mvdev->actual_features & BIT_ULL(VIRTIO_NET_F_CTRL_VQ)) {
+		u16 last_avail_idx = cvq->vring.last_avail_idx;
+
 		err = vringh_init_iotlb(&cvq->vring, mvdev->actual_features,
 					MLX5_CVQ_MAX_ENT, false,
 					(struct vring_desc *)(uintptr_t)cvq->desc_addr,
 					(struct vring_avail *)(uintptr_t)cvq->driver_addr,
 					(struct vring_used *)(uintptr_t)cvq->device_addr);
 
+		if (!err)
+			vringh_set_base_iotlb(&cvq->vring, last_avail_idx);
+	}
 	return err;
 }
 
diff --git a/drivers/vhost/vringh.c b/drivers/vhost/vringh.c
index 7b8fd977f71c..799762c83007 100644
--- a/drivers/vhost/vringh.c
+++ b/drivers/vhost/vringh.c
@@ -595,6 +595,24 @@ static inline void __vringh_notify_disable(struct vringh *vrh,
 	}
 }
 
+static inline int __vringh_set_base(struct vringh *vrh, u16 idx,
+	                    int (*putu16)(const struct vringh *vrh,
+	                        __virtio16 *p, u16 val))
+{
+    int ret;
+
+    ret = putu16(vrh, &vrh->vring.avail->idx, idx);
+    if (ret)
+        return ret;
+
+    ret = putu16(vrh, &vrh->vring.used->idx, idx);
+    if (ret)
+        return ret;
+
+    vrh->last_avail_idx = vrh->last_used_idx = idx;
+    return 0;
+}
+
 /* Userspace access helpers: in this case, addresses are really userspace. */
 static inline int getu16_user(const struct vringh *vrh, u16 *val, const __virtio16 *p)
 {
@@ -1456,6 +1474,18 @@ void vringh_set_iotlb(struct vringh *vrh, struct vhost_iotlb *iotlb,
 }
 EXPORT_SYMBOL(vringh_set_iotlb);
 
+/**
+ * vringh_set_base_iotlb - set avail_idx and used_idx
+ * @vrh: the vring
+ * @idx: the value to set
+ */
+int vringh_set_base_iotlb(struct vringh *vrh, u16 idx)
+{
+    return __vringh_set_base(vrh, idx, putu16_iotlb);
+}
+EXPORT_SYMBOL(vringh_set_base_iotlb);
+
+
 /**
  * vringh_getdesc_iotlb - get next available descriptor from ring with
  * IOTLB.
diff --git a/include/linux/vringh.h b/include/linux/vringh.h
index c3a8117dabe8..e9b8af4e6a5e 100644
--- a/include/linux/vringh.h
+++ b/include/linux/vringh.h
@@ -306,6 +306,8 @@ int vringh_init_iotlb_va(struct vringh *vrh, u64 features,
 			 struct vring_avail *avail,
 			 struct vring_used *used);
 
+int vringh_set_base_iotlb(struct vringh *vrh, u16 idx);
+
 int vringh_getdesc_iotlb(struct vringh *vrh,
 			 struct vringh_kiov *riov,
 			 struct vringh_kiov *wiov,
-- 
2.39.3

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