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Message-ID: <e9ca64b4-3196-4b7b-822c-4bb0b40f8689@daynix.com>
Date: Fri, 20 Jun 2025 00:00:34 +0900
From: Akihiko Odaki <akihiko.odaki@...nix.com>
To: Paolo Abeni <pabeni@...hat.com>, netdev@...r.kernel.org
Cc: Willem de Bruijn <willemdebruijn.kernel@...il.com>,
Jason Wang <jasowang@...hat.com>, Andrew Lunn <andrew+netdev@...n.ch>,
"David S. Miller" <davem@...emloft.net>, Eric Dumazet <edumazet@...gle.com>,
Jakub Kicinski <kuba@...nel.org>, "Michael S. Tsirkin" <mst@...hat.com>,
Xuan Zhuo <xuanzhuo@...ux.alibaba.com>, Eugenio Pérez
<eperezma@...hat.com>, Yuri Benditovich <yuri.benditovich@...nix.com>
Subject: Re: [PATCH v4 net-next 3/8] vhost-net: allow configuring extended
features
On 2025/06/18 1:12, Paolo Abeni wrote:
> 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 <jasowang@...hat.com>
> Signed-off-by: Paolo Abeni <pabeni@...hat.com>
> ---
> v3 -> v4:
> - use a single static (lower case) constant instead of enum and old def
> - simpler VHOST_GET_FEATURES_ARRAY impl
> - avoid using virtio_features_and_not
>
> v2 -> v3:
> - virtio_features_t -> u64[2]
> - add __counted_by annotation to vhost_features_array
>
> v1 -> v2:
> - change the ioctl to use an extensible API
> ---
> drivers/vhost/net.c | 87 ++++++++++++++++++++++++--------
> drivers/vhost/vhost.c | 2 +-
> drivers/vhost/vhost.h | 4 +-
> include/uapi/linux/vhost.h | 7 +++
> include/uapi/linux/vhost_types.h | 5 ++
> 5 files changed, 82 insertions(+), 23 deletions(-)
>
> diff --git a/drivers/vhost/net.c b/drivers/vhost/net.c
> index 7cbfc7d718b3..126aa4ee26a8 100644
> --- a/drivers/vhost/net.c
> +++ b/drivers/vhost/net.c
> @@ -69,12 +69,12 @@ MODULE_PARM_DESC(experimental_zcopytx, "Enable Zero Copy TX;"
>
> #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 {
> @@ -1614,16 +1614,17 @@ static long vhost_net_reset_owner(struct vhost_net *n)
> 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;
> @@ -1633,18 +1634,19 @@ static int vhost_net_set_features(struct vhost_net *n, u64 features)
> 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);
> @@ -1681,12 +1683,13 @@ static long vhost_net_set_owner(struct vhost_net *n)
> 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:
> @@ -1694,16 +1697,60 @@ static long vhost_net_ioctl(struct file *f, unsigned int ioctl,
> 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, argp, sizeof(u64)))
> + 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, (count - copied) * sizeof(u64)))
> + return -EFAULT;
> + return 0;
> + case VHOST_SET_FEATURES_ARRAY:
> + if (copy_from_user(&count, argp, sizeof(u64)))
> + return -EFAULT;
> +
> + virtio_features_zero(all_features);
> + for (i = 0; i < min(count, VIRTIO_FEATURES_DWORDS); ++i) {
> + argp += sizeof(u64);
> + if (copy_from_user(&all_features[i], argp,
> + sizeof(u64)))
> + return -EFAULT;
> + }
This for loop can be converted into a single copy_from_user() call as
done for VHOST_GET_FEATURES_ARRAY/copy_to_user().
> +
> + /* Any feature specified by user-space above VIRTIO_FEATURES_MAX is
> + * not supported by definition.
> + */
> + for (; i < count; ++i) {
> + if (copy_from_user(&features, argp, sizeof(u64)))
get_user() is a simpler alternative.
> + return -EFAULT;
> + if (features)
> + return -EOPNOTSUPP;
> + }
> +
> + for (i = 1; i < VIRTIO_FEATURES_DWORDS; i++)
i should be initialized with 0 to check the first element as done for
VHOST_SET_FEATURES.
> + 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)))
> diff --git a/drivers/vhost/vhost.c b/drivers/vhost/vhost.c
> index 3a5ebb973dba..1094256a943c 100644
> --- a/drivers/vhost/vhost.c
> +++ b/drivers/vhost/vhost.c
> @@ -372,7 +372,7 @@ static void vhost_vq_reset(struct vhost_dev *dev,
> 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;
> diff --git a/drivers/vhost/vhost.h b/drivers/vhost/vhost.h
> index bb75a292d50c..d1aed35c4b07 100644
> --- a/drivers/vhost/vhost.h
> +++ b/drivers/vhost/vhost.h
> @@ -133,7 +133,7 @@ struct vhost_virtqueue {
> 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;
> @@ -291,7 +291,7 @@ static inline void *vhost_vq_get_backend(struct vhost_virtqueue *vq)
>
> 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)
> diff --git a/include/uapi/linux/vhost.h b/include/uapi/linux/vhost.h
> index d4b3e2ae1314..d6ad01fbb8d2 100644
> --- a/include/uapi/linux/vhost.h
> +++ b/include/uapi/linux/vhost.h
> @@ -235,4 +235,11 @@
> */
> #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
> diff --git a/include/uapi/linux/vhost_types.h b/include/uapi/linux/vhost_types.h
> index d7656908f730..1c39cc5f5a31 100644
> --- a/include/uapi/linux/vhost_types.h
> +++ b/include/uapi/linux/vhost_types.h
> @@ -110,6 +110,11 @@ struct vhost_msg_v2 {
> };
> };
>
> +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 */
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