vhost-net: allow configuring extended features

Use the extended feature type for 'acked_features' and implement
two new ioctls operation allowing the user-space to set/query an
unbounded amount of features.

The actual number of processed features is limited by VIRTIO_FEATURES_MAX
and attempts to set features above such limit fail with
EOPNOTSUPP.

Note that: the legacy ioctls implicitly truncate the negotiated
features to the lower 64 bits range and the 'acked_backend_features'
field don't need conversion, as the only negotiated feature there
is in the low 64 bit range.

Acked-by: Jason Wang <[e-mail]>
Signed-off-by: Paolo Abeni <[e-mail]>

drivers/vhost/net.c

···
 
 #define VHOST_DMA_IS_DONE(len) ((__force u32)(len) >= (__force u32)VHOST_DMA_DONE_LEN)
 
-enum {
-	VHOST_NET_FEATURES = VHOST_FEATURES |
-			 (1ULL << VHOST_NET_F_VIRTIO_NET_HDR) |
-			 (1ULL << VIRTIO_NET_F_MRG_RXBUF) |
-			 (1ULL << VIRTIO_F_ACCESS_PLATFORM) |
-			 (1ULL << VIRTIO_F_RING_RESET)
+static const u64 vhost_net_features[VIRTIO_FEATURES_DWORDS] = {
+	VHOST_FEATURES |
+	(1ULL << VHOST_NET_F_VIRTIO_NET_HDR) |
+	(1ULL << VIRTIO_NET_F_MRG_RXBUF) |
+	(1ULL << VIRTIO_F_ACCESS_PLATFORM) |
+	(1ULL << VIRTIO_F_RING_RESET),
 };
 
 enum {
···
 	return err;
 }
 
-static int vhost_net_set_features(struct vhost_net *n, u64 features)
+static int vhost_net_set_features(struct vhost_net *n, const u64 *features)
 {
 	size_t vhost_hlen, sock_hlen, hdr_len;
 	int i;
 
-	hdr_len = (features & ((1ULL << VIRTIO_NET_F_MRG_RXBUF) |
-			       (1ULL << VIRTIO_F_VERSION_1))) ?
-			sizeof(struct virtio_net_hdr_mrg_rxbuf) :
-			sizeof(struct virtio_net_hdr);
-	if (features & (1 << VHOST_NET_F_VIRTIO_NET_HDR)) {
+	hdr_len = virtio_features_test_bit(features, VIRTIO_NET_F_MRG_RXBUF) ||
+		  virtio_features_test_bit(features, VIRTIO_F_VERSION_1) ?
+		  sizeof(struct virtio_net_hdr_mrg_rxbuf) :
+		  sizeof(struct virtio_net_hdr);
+
+	if (virtio_features_test_bit(features, VHOST_NET_F_VIRTIO_NET_HDR)) {
 		/* vhost provides vnet_hdr */
 		vhost_hlen = hdr_len;
 		sock_hlen = 0;
···
 		sock_hlen = hdr_len;
 	}
 	mutex_lock(&n->dev.mutex);
-	if ((features & (1 << VHOST_F_LOG_ALL)) &&
+	if (virtio_features_test_bit(features, VHOST_F_LOG_ALL) &&
 	    !vhost_log_access_ok(&n->dev))
 		goto out_unlock;
 
-	if ((features & (1ULL << VIRTIO_F_ACCESS_PLATFORM))) {
+	if (virtio_features_test_bit(features, VIRTIO_F_ACCESS_PLATFORM)) {
 		if (vhost_init_device_iotlb(&n->dev))
 			goto out_unlock;
 	}
 
 	for (i = 0; i < VHOST_NET_VQ_MAX; ++i) {
 		mutex_lock(&n->vqs[i].vq.mutex);
-		n->vqs[i].vq.acked_features = features;
+		virtio_features_copy(n->vqs[i].vq.acked_features_array,
+				     features);
 		n->vqs[i].vhost_hlen = vhost_hlen;
 		n->vqs[i].sock_hlen = sock_hlen;
 		mutex_unlock(&n->vqs[i].vq.mutex);
···
 static long vhost_net_ioctl(struct file *f, unsigned int ioctl,
 			    unsigned long arg)
 {
+	u64 all_features[VIRTIO_FEATURES_DWORDS];
 	struct vhost_net *n = f->private_data;
 	void __user *argp = (void __user *)arg;
 	u64 __user *featurep = argp;
 	struct vhost_vring_file backend;
-	u64 features;
-	int r;
+	u64 features, count, copied;
+	int r, i;
 
 	switch (ioctl) {
 	case VHOST_NET_SET_BACKEND:
···
 			return -EFAULT;
 		return vhost_net_set_backend(n, backend.index, backend.fd);
 	case VHOST_GET_FEATURES:
-		features = VHOST_NET_FEATURES;
+		features = vhost_net_features[0];
 		if (copy_to_user(featurep, &features, sizeof features))
 			return -EFAULT;
 		return 0;
 	case VHOST_SET_FEATURES:
 		if (copy_from_user(&features, featurep, sizeof features))
 			return -EFAULT;
-		if (features & ~VHOST_NET_FEATURES)
+		if (features & ~vhost_net_features[0])
 			return -EOPNOTSUPP;
-		return vhost_net_set_features(n, features);
+
+		virtio_features_from_u64(all_features, features);
+		return vhost_net_set_features(n, all_features);
+	case VHOST_GET_FEATURES_ARRAY:
+		if (copy_from_user(&count, featurep, sizeof(count)))
+			return -EFAULT;
+
+		/* Copy the net features, up to the user-provided buffer size */
+		argp += sizeof(u64);
+		copied = min(count, VIRTIO_FEATURES_DWORDS);
+		if (copy_to_user(argp, vhost_net_features,
+				 copied * sizeof(u64)))
+			return -EFAULT;
+
+		/* Zero the trailing space provided by user-space, if any */
+		if (clear_user(argp, size_mul(count - copied, sizeof(u64))))
+			return -EFAULT;
+		return 0;
+	case VHOST_SET_FEATURES_ARRAY:
+		if (copy_from_user(&count, featurep, sizeof(count)))
+			return -EFAULT;
+
+		virtio_features_zero(all_features);
+		argp += sizeof(u64);
+		copied = min(count, VIRTIO_FEATURES_DWORDS);
+		if (copy_from_user(all_features, argp, copied * sizeof(u64)))
+			return -EFAULT;
+
+		/*
+		 * Any feature specified by user-space above
+		 * VIRTIO_FEATURES_MAX is not supported by definition.
+		 */
+		for (i = copied; i < count; ++i) {
+			if (copy_from_user(&features, featurep + 1 + i,
+					   sizeof(features)))
+				return -EFAULT;
+			if (features)
+				return -EOPNOTSUPP;
+		}
+
+		for (i = 0; i < VIRTIO_FEATURES_DWORDS; i++)
+			if (all_features[i] & ~vhost_net_features[i])
+				return -EOPNOTSUPP;
+
+		return vhost_net_set_features(n, all_features);
 	case VHOST_GET_BACKEND_FEATURES:
 		features = VHOST_NET_BACKEND_FEATURES;
 		if (copy_to_user(featurep, &features, sizeof(features)))

drivers/vhost/vhost.c

···
 	vq->log_used = false;
 	vq->log_addr = -1ull;
 	vq->private_data = NULL;
-	vq->acked_features = 0;
+	virtio_features_zero(vq->acked_features_array);
 	vq->acked_backend_features = 0;
 	vq->log_base = NULL;
 	vq->error_ctx = NULL;

drivers/vhost/vhost.h

···
 	struct vhost_iotlb *umem;
 	struct vhost_iotlb *iotlb;
 	void *private_data;
-	u64 acked_features;
+	VIRTIO_DECLARE_FEATURES(acked_features);
 	u64 acked_backend_features;
 	/* Log write descriptors */
 	void __user *log_base;
···
 
 static inline bool vhost_has_feature(struct vhost_virtqueue *vq, int bit)
 {
-	return vq->acked_features & (1ULL << bit);
+	return virtio_features_test_bit(vq->acked_features_array, bit);
 }
 
 static inline bool vhost_backend_has_feature(struct vhost_virtqueue *vq, int bit)

include/uapi/linux/vhost.h

···
  */
 #define VHOST_VDPA_GET_VRING_SIZE	_IOWR(VHOST_VIRTIO, 0x82,	\
 					      struct vhost_vring_state)
+
+/* Extended features manipulation */
+#define VHOST_GET_FEATURES_ARRAY _IOR(VHOST_VIRTIO, 0x83, \
+				       struct vhost_features_array)
+#define VHOST_SET_FEATURES_ARRAY _IOW(VHOST_VIRTIO, 0x83, \
+				       struct vhost_features_array)
+
 #endif

include/uapi/linux/vhost_types.h

···
 	};
 };
 
+struct vhost_features_array {
+	__u64 count; /* number of entries present in features array */
+	__u64 features[] __counted_by(count);
+};
+
 struct vhost_memory_region {
 	__u64 guest_phys_addr;
 	__u64 memory_size; /* bytes */