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Message-ID: <20220815114900-mutt-send-email-mst@kernel.org>
Date: Mon, 15 Aug 2022 11:52:40 -0400
From: "Michael S. Tsirkin" <mst@...hat.com>
To: Zhu Lingshan <lingshan.zhu@...el.com>
Cc: jasowang@...hat.com, virtualization@...ts.linux-foundation.org,
netdev@...r.kernel.org, kvm@...r.kernel.org, parav@...dia.com,
xieyongji@...edance.com, gautam.dawar@....com
Subject: Re: [PATCH 2/2] vDPA: conditionally read fields in virtio-net dev
On Mon, Aug 15, 2022 at 05:26:38PM +0800, Zhu Lingshan wrote:
> Some fields of virtio-net device config space are
> conditional on the feature bits, the spec says:
>
> "The mac address field always exists
> (though is only valid if VIRTIO_NET_F_MAC is set)"
>
> "max_virtqueue_pairs only exists if VIRTIO_NET_F_MQ
> or VIRTIO_NET_F_RSS is set"
>
> "mtu only exists if VIRTIO_NET_F_MTU is set"
>
> so we should read MTU, MAC and MQ in the device config
> space only when these feature bits are offered.
>
> For MQ, if both VIRTIO_NET_F_MQ and VIRTIO_NET_F_RSS are
> not set, the virtio device should have
> one queue pair as default value, so when userspace querying queue pair numbers,
> it should return mq=1 than zero.
>
> For MTU, if VIRTIO_NET_F_MTU is not set, we should not read
> MTU from the device config sapce.
> RFC894 <A Standard for the Transmission of IP Datagrams over Ethernet Networks>
> says:"The minimum length of the data field of a packet sent over an
> Ethernet is 1500 octets, thus the maximum length of an IP datagram
> sent over an Ethernet is 1500 octets. Implementations are encouraged
> to support full-length packets"
>
> virtio spec says:"The virtio network device is a virtual ethernet card",
> so the default MTU value should be 1500 for virtio-net.
>
> For MAC, the spec says:"If the VIRTIO_NET_F_MAC feature bit is set,
> the configuration space mac entry indicates the “physical” address
> of the network card, otherwise the driver would typically
> generate a random local MAC address." So there is no
> default MAC address if VIRTIO_NET_F_MAC not set.
>
> This commits introduces functions vdpa_dev_net_mtu_config_fill()
> and vdpa_dev_net_mac_config_fill() to fill MTU and MAC.
> It also fixes vdpa_dev_net_mq_config_fill() to report correct
> MQ when _F_MQ is not present.
>
> These functions should check devices features than driver
> features, and struct vdpa_device is not needed as a parameter
>
> The test & userspace tool output:
>
> Feature bit VIRTIO_NET_F_MTU, VIRTIO_NET_F_RSS, VIRTIO_NET_F_MQ
> and VIRTIO_NET_F_MAC can be mask out by hardcode.
>
> However, it is challenging to "disable" the related fields
> in the HW device config space, so let's just assume the values
> are meaningless if the feature bits are not set.
>
> Before this change, when feature bits for RSS, MQ, MTU and MAC
> are not set, iproute2 output:
> $vdpa vdpa0: mac 00:e8:ca:11:be:05 link up link_announce false mtu 1500
> negotiated_features
where does it get 1500? what if there's e.g. 0 in the mtu field?
> without this commit, function vdpa_dev_net_config_fill()
> reads all config space fields unconditionally, so let's
> assume the MAC and MTU are meaningless, and it checks
> MQ with driver_features, so we don't see max_vq_pairs.
>
> After applying this commit, when feature bits for
> MQ, RSS, MAC and MTU are not set,iproute2 output:
> $vdpa dev config show vdpa0
> vdpa0: link up link_announce false max_vq_pairs 1 mtu 1500
> negotiated_features
>
> As explained above:
> Here is no MAC, because VIRTIO_NET_F_MAC is not set,
> and there is no default value for MAC. It shows
> max_vq_paris = 1 because even without MQ feature,
> a functional virtio-net must have one queue pair.
> mtu = 1500 is the default value as ethernet
> required.
>
> This commit also add supplementary comments for
> __virtio16_to_cpu(true, xxx) operations in
> vdpa_dev_net_config_fill() and vdpa_fill_stats_rec()
>
> Signed-off-by: Zhu Lingshan <lingshan.zhu@...el.com>
> ---
> drivers/vdpa/vdpa.c | 60 +++++++++++++++++++++++++++++++++++----------
> 1 file changed, 47 insertions(+), 13 deletions(-)
>
> diff --git a/drivers/vdpa/vdpa.c b/drivers/vdpa/vdpa.c
> index efb55a06e961..a74660b98979 100644
> --- a/drivers/vdpa/vdpa.c
> +++ b/drivers/vdpa/vdpa.c
> @@ -801,19 +801,44 @@ static int vdpa_nl_cmd_dev_get_dumpit(struct sk_buff *msg, struct netlink_callba
> return msg->len;
> }
>
> -static int vdpa_dev_net_mq_config_fill(struct vdpa_device *vdev,
> - struct sk_buff *msg, u64 features,
> +static int vdpa_dev_net_mq_config_fill(struct sk_buff *msg, u64 features,
> const struct virtio_net_config *config)
> {
> u16 val_u16;
>
> - if ((features & BIT_ULL(VIRTIO_NET_F_MQ)) == 0)
> - return 0;
> + if ((features & BIT_ULL(VIRTIO_NET_F_MQ)) == 0 &&
> + (features & BIT_ULL(VIRTIO_NET_F_RSS)) == 0)
> + val_u16 = 1;
> + else
> + val_u16 = __virtio16_to_cpu(true, config->max_virtqueue_pairs);
>
> - val_u16 = le16_to_cpu(config->max_virtqueue_pairs);
> return nla_put_u16(msg, VDPA_ATTR_DEV_NET_CFG_MAX_VQP, val_u16);
> }
>
> +static int vdpa_dev_net_mtu_config_fill(struct sk_buff *msg, u64 features,
> + const struct virtio_net_config *config)
> +{
> + u16 val_u16;
> +
> + if ((features & BIT_ULL(VIRTIO_NET_F_MTU)) == 0)
> + val_u16 = 1500;
> + else
> + val_u16 = __virtio16_to_cpu(true, config->mtu);
> +
> + return nla_put_u16(msg, VDPA_ATTR_DEV_NET_CFG_MTU, val_u16);
> +}
> +
> +static int vdpa_dev_net_mac_config_fill(struct sk_buff *msg, u64 features,
> + const struct virtio_net_config *config)
> +{
> + if ((features & BIT_ULL(VIRTIO_NET_F_MAC)) == 0)
> + return 0;
> + else
> + return nla_put(msg, VDPA_ATTR_DEV_NET_CFG_MACADDR,
> + sizeof(config->mac), config->mac);
> +}
> +
> +
> static int vdpa_dev_net_config_fill(struct vdpa_device *vdev, struct sk_buff *msg)
> {
> struct virtio_net_config config = {};
> @@ -822,18 +847,16 @@ static int vdpa_dev_net_config_fill(struct vdpa_device *vdev, struct sk_buff *ms
>
> vdpa_get_config_unlocked(vdev, 0, &config, sizeof(config));
>
> - if (nla_put(msg, VDPA_ATTR_DEV_NET_CFG_MACADDR, sizeof(config.mac),
> - config.mac))
> - return -EMSGSIZE;
> + /*
> + * Assume little endian for now, userspace can tweak this for
> + * legacy guest support.
> + */
> + val_u16 = __virtio16_to_cpu(true, config.status);
>
> val_u16 = __virtio16_to_cpu(true, config.status);
> if (nla_put_u16(msg, VDPA_ATTR_DEV_NET_STATUS, val_u16))
> return -EMSGSIZE;
>
> - val_u16 = __virtio16_to_cpu(true, config.mtu);
> - if (nla_put_u16(msg, VDPA_ATTR_DEV_NET_CFG_MTU, val_u16))
> - return -EMSGSIZE;
> -
> features_driver = vdev->config->get_driver_features(vdev);
> if (nla_put_u64_64bit(msg, VDPA_ATTR_DEV_NEGOTIATED_FEATURES, features_driver,
> VDPA_ATTR_PAD))
> @@ -846,7 +869,13 @@ static int vdpa_dev_net_config_fill(struct vdpa_device *vdev, struct sk_buff *ms
> VDPA_ATTR_PAD))
> return -EMSGSIZE;
>
> - return vdpa_dev_net_mq_config_fill(vdev, msg, features_driver, &config);
> + if (vdpa_dev_net_mac_config_fill(msg, features_device, &config))
> + return -EMSGSIZE;
> +
> + if (vdpa_dev_net_mtu_config_fill(msg, features_device, &config))
> + return -EMSGSIZE;
> +
> + return vdpa_dev_net_mq_config_fill(msg, features_device, &config);
> }
>
> static int
> @@ -914,6 +943,11 @@ static int vdpa_fill_stats_rec(struct vdpa_device *vdev, struct sk_buff *msg,
> }
> vdpa_get_config_unlocked(vdev, 0, &config, sizeof(config));
>
> + /*
> + * Assume little endian for now, userspace can tweak this for
> + * legacy guest support.
> + */
> +
> max_vqp = __virtio16_to_cpu(true, config.max_virtqueue_pairs);
> if (nla_put_u16(msg, VDPA_ATTR_DEV_NET_CFG_MAX_VQP, max_vqp))
> return -EMSGSIZE;
> --
> 2.31.1
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