On Wed, May 11, 2022 at 05:34:25PM +0800, Jason Wang wrote:
> On Wed, May 11, 2022 at 4:48 PM Eli Cohen <elic@xxxxxxxxxx> wrote:
> >
> > Following the recommendation in virio spec 1.1, a device offering
> > VIRTIO_NET_F_MTU should set the mtu to at least 1280 bytes.
> >
> > Print a warning if this recommendation is not met.
> >
> > Signed-off-by: Eli Cohen <elic@xxxxxxxxxx>
>
> I wonder why it's a must?
It's a SHOULD in the spec. I guess 1280 is to allow IPv6.
> > ---
> > drivers/vdpa/vdpa.c | 9 ++++++++-
> > 1 file changed, 8 insertions(+), 1 deletion(-)
> >
> > diff --git a/drivers/vdpa/vdpa.c b/drivers/vdpa/vdpa.c
> > index 91f4c13c7c7c..961168fe9094 100644
> > --- a/drivers/vdpa/vdpa.c
> > +++ b/drivers/vdpa/vdpa.c
> > @@ -583,6 +583,9 @@ vdpa_nl_cmd_mgmtdev_get_dumpit(struct sk_buff *msg, struct netlink_callback *cb)
> > BIT_ULL(VDPA_ATTR_DEV_NET_CFG_MTU) | \
> > BIT_ULL(VDPA_ATTR_DEV_NET_CFG_MAX_VQP))
> >
> > +/* Recommended virtio spec 1.1 section 5.1.4.1 */
> > +#define VIRTIO_MIN_PREFERRED_MTU 1280
> > +
> > static int vdpa_nl_cmd_dev_add_set_doit(struct sk_buff *skb, struct genl_info *info)
> > {
> > struct vdpa_dev_set_config config = {};
> > @@ -634,6 +637,10 @@ static int vdpa_nl_cmd_dev_add_set_doit(struct sk_buff *skb, struct genl_info *i
> > err = PTR_ERR(mdev);
> > goto err;
> > }
> > + if ((mdev->supported_features & BIT_ULL(VIRTIO_NET_F_MTU)) &&
> > + (config.mask & BIT_ULL(VDPA_ATTR_DEV_NET_CFG_MTU) &&
> > + config.net.mtu < VIRTIO_MIN_PREFERRED_MTU))
>
> Should be <= ?
>
> Thanks
> > + pr_warn("MTU is below recommended value\n");
> > if ((config.mask & mdev->config_attr_mask) != config.mask) {
> > NL_SET_ERR_MSG_MOD(info->extack,
> > "All provided attributes are not supported");
> > @@ -1135,7 +1142,7 @@ static const struct nla_policy vdpa_nl_policy[VDPA_ATTR_MAX + 1] = {
> > [VDPA_ATTR_DEV_NAME] = { .type = NLA_STRING },
> > [VDPA_ATTR_DEV_NET_CFG_MACADDR] = NLA_POLICY_ETH_ADDR,
> > /* virtio spec 1.1 section 5.1.4.1 for valid MTU range */
> > - [VDPA_ATTR_DEV_NET_CFG_MTU] = NLA_POLICY_MIN(NLA_U16, 68),
> > + [VDPA_ATTR_DEV_NET_CFG_MTU] = NLA_POLICY_MIN(NLA_U16, ETH_MIN_MTU),
> > };
> >
> > static const struct genl_ops vdpa_nl_ops[] = {
> > --
> > 2.35.1
> >
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