RE: [PATCH v1] vdpa: Warn if MTU configured is too low

[Eli Cohen]

> -----Original Message-----
> From: Michael S. Tsirkin <mst@xxxxxxxxxx>
> Sent: Thursday, May 12, 2022 8:57 AM
> To: Eli Cohen <elic@xxxxxxxxxx>
> Cc: jasowang@xxxxxxxxxx; virtualization@xxxxxxxxxxxxxxxxxxxxxxxxxx; linux-kernel@xxxxxxxxxxxxxxx; si-wei.liu@xxxxxxxxxx
> Subject: Re: [PATCH v1] vdpa: Warn if MTU configured is too low
> 
> On Wed, May 11, 2022 at 01:56:42PM +0300, Eli Cohen 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>
> > ---
> > v0 -> v1:
> >   chage pr_warn to netlink warning to userspace
> >
> >  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..0fb4a615f267 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 */
> 
> I'd add name of section here too.

Sure

> 
> > +#define VIRTIO_MIN_PREFERRED_MTU 1280
> > +
> 
> Preferred is kind of confusing here. I guess you are trying to
> say it's not mandatory but I don't think this conveys this information.
> 
> Recommended (matching text below)?

Will modify

> 
> 
> >  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))
> > +		NL_SET_ERR_MSG_MOD(info->extack, "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");
> 
> 
> Pity we can't include the actual value here, but oh well. At least let's
> include the recommended value, we can do that:
> 	"MTU is below recommended value of " __stringify(VIRTIO_MIN_PREFERRED_MTU) "\n"
> 
Will change
> 
> > @@ -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