vdpa/mlx5: Add support for doorbell bypassing

Implement mlx5_get_vq_notification() to return the doorbell address.
Since the notification area is mapped to userspace, make sure that the
BAR size is at least PAGE_SIZE large.
Signed-off-by: Eli Cohen <elic@nvidia.com>
Link: https://lore.kernel.org/r/20210603081153.5750-1-elic@nvidia.comSigned-off-by: Michael S. Tsirkin <mst@redhat.com>
Acked-by: Jason Wang <jasowang@redhat.com>

drivers/vdpa/mlx5/core/mlx5_vdpa.h

@@ -42,6 +42,7 @@ struct mlx5_vdpa_resources {
 	u32 pdn;
 	struct mlx5_uars_page *uar;
 	void __iomem *kick_addr;
+	u64 phys_kick_addr;
 	u16 uid;
 	u32 null_mkey;
 	bool valid;

drivers/vdpa/mlx5/core/resources.c

@@ -253,6 +253,7 @@ int mlx5_vdpa_alloc_resources(struct mlx5_vdpa_dev *mvdev)
 		goto err_key;
 
 	kick_addr = mdev->bar_addr + offset;
+	res->phys_kick_addr = kick_addr;
 
 	res->kick_addr = ioremap(kick_addr, PAGE_SIZE);
 	if (!res->kick_addr) {

drivers/vdpa/mlx5/net/mlx5_vnet.c

@@ -1876,8 +1876,22 @@ static void mlx5_vdpa_free(struct vdpa_device *vdev)
 
 static struct vdpa_notification_area mlx5_get_vq_notification(struct vdpa_device *vdev, u16 idx)
 {
+	struct mlx5_vdpa_dev *mvdev = to_mvdev(vdev);
 	struct vdpa_notification_area ret = {};
+	struct mlx5_vdpa_net *ndev;
+	phys_addr_t addr;
 
+	/* If SF BAR size is smaller than PAGE_SIZE, do not use direct
+	 * notification to avoid the risk of mapping pages that contain BAR of more
+	 * than one SF
+	 */
+	if (MLX5_CAP_GEN(mvdev->mdev, log_min_sf_size) + 12 < PAGE_SHIFT)
+		return ret;
+
+	ndev = to_mlx5_vdpa_ndev(mvdev);
+	addr = (phys_addr_t)ndev->mvdev.res.phys_kick_addr;
+	ret.addr = addr;
+	ret.size = PAGE_SIZE;
 	return ret;
 }