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Tsirkin" To: Jason Wang Cc: Eli Cohen , virtualization , linux-kernel , Si-Wei Liu Subject: Re: [PATCH] vdpa: Warn if MTU configured is too low Message-ID: <20220511055517-mutt-send-email-mst@kernel.org> References: <20220511084804.82482-1-elic@nvidia.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Wed, May 11, 2022 at 05:34:25PM +0800, Jason Wang wrote: > On Wed, May 11, 2022 at 4:48 PM 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 > > 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 > >