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Date: Tue, 21 Apr 2020 06:59:19 -0600
From: David Ahern <dsahern@...il.com>
To: Toke Høiland-Jørgensen <toke@...hat.com>,
David Ahern <dsahern@...nel.org>, netdev@...r.kernel.org
Cc: davem@...emloft.net, kuba@...nel.org,
prashantbhole.linux@...il.com, jasowang@...hat.com,
brouer@...hat.com, toshiaki.makita1@...il.com,
daniel@...earbox.net, john.fastabend@...il.com, ast@...nel.org,
kafai@...com, songliubraving@...com, yhs@...com, andriin@...com,
David Ahern <dahern@...italocean.com>
Subject: Re: [PATCH bpf-next 06/16] net: Add IFLA_XDP_EGRESS for XDP programs
in the egress path
On 4/21/20 4:17 AM, Toke Høiland-Jørgensen wrote:
> David Ahern <dsahern@...nel.org> writes:
>
>> From: David Ahern <dahern@...italocean.com>
>>
>> Running programs in the egress path, on skbs or xdp_frames, does not
>> require driver specific resources like Rx path. Accordingly, the
>> programs can be run in core code, so add xdp_egress_prog to net_device
>> to hold a reference to an attached program.
>>
>> For UAPI, add IFLA_XDP_EGRESS to if_link.h to specify egress programs,
>> add a new attach flag, XDP_ATTACHED_EGRESS_CORE, to denote the
>> attach point is at the core level (as opposed to driver or hardware)
>> and add IFLA_XDP_EGRESS_CORE_PROG_ID for reporting the program id.
>>
>> Add egress argument to do_setlink_xdp to denote processing of
>> IFLA_XDP_EGRESS versus IFLA_XDP, and add a check that none of the
>> existing modes (SKB, DRV or HW) are set since those modes are not
>> valid. The expectation is that XDP_FLAGS_HW_MODE will be used later
>> (e.g., offloading guest programs).
>>
>> Add rtnl_xdp_egress_fill and helpers as the egress counterpart to the
>> existing rtnl_xdp_fill.
>>
>> Signed-off-by: David Ahern <dahern@...italocean.com>
>> ---
>> include/linux/netdevice.h | 1 +
>> include/uapi/linux/if_link.h | 3 +
>> net/core/rtnetlink.c | 96 ++++++++++++++++++++++++++++--
>> tools/include/uapi/linux/if_link.h | 3 +
>> 4 files changed, 99 insertions(+), 4 deletions(-)
>>
>> diff --git a/include/linux/netdevice.h b/include/linux/netdevice.h
>> index d0bb9e09660a..3133247681fd 100644
>> --- a/include/linux/netdevice.h
>> +++ b/include/linux/netdevice.h
>> @@ -1995,6 +1995,7 @@ struct net_device {
>> unsigned int real_num_rx_queues;
>>
>> struct bpf_prog __rcu *xdp_prog;
>> + struct bpf_prog __rcu *xdp_egress_prog;
>> unsigned long gro_flush_timeout;
>> rx_handler_func_t __rcu *rx_handler;
>> void __rcu *rx_handler_data;
>> diff --git a/include/uapi/linux/if_link.h b/include/uapi/linux/if_link.h
>> index 127c704eeba9..b3c6cb2f0f0a 100644
>> --- a/include/uapi/linux/if_link.h
>> +++ b/include/uapi/linux/if_link.h
>> @@ -170,6 +170,7 @@ enum {
>> IFLA_PROP_LIST,
>> IFLA_ALT_IFNAME, /* Alternative ifname */
>> IFLA_PERM_ADDRESS,
>> + IFLA_XDP_EGRESS, /* nested attribute with 1 or more IFLA_XDP_ attrs */
>> __IFLA_MAX
>> };
>>
>> @@ -988,6 +989,7 @@ enum {
>> XDP_ATTACHED_SKB,
>> XDP_ATTACHED_HW,
>> XDP_ATTACHED_MULTI,
>> + XDP_ATTACHED_EGRESS_CORE,
>> };
>>
>> enum {
>> @@ -1000,6 +1002,7 @@ enum {
>> IFLA_XDP_SKB_PROG_ID,
>> IFLA_XDP_HW_PROG_ID,
>> IFLA_XDP_EXPECTED_FD,
>> + IFLA_XDP_EGRESS_CORE_PROG_ID,
>> __IFLA_XDP_MAX,
>> };
>>
>> diff --git a/net/core/rtnetlink.c b/net/core/rtnetlink.c
>> index dc44af16226a..e9bc5cee06c8 100644
>> --- a/net/core/rtnetlink.c
>> +++ b/net/core/rtnetlink.c
>> @@ -1030,7 +1030,7 @@ static noinline size_t if_nlmsg_size(const struct net_device *dev,
>> + nla_total_size(MAX_PHYS_ITEM_ID_LEN) /* IFLA_PHYS_PORT_ID */
>> + nla_total_size(MAX_PHYS_ITEM_ID_LEN) /* IFLA_PHYS_SWITCH_ID */
>> + nla_total_size(IFNAMSIZ) /* IFLA_PHYS_PORT_NAME */
>> - + rtnl_xdp_size() /* IFLA_XDP */
>> + + rtnl_xdp_size() * 2 /* IFLA_XDP and IFLA_XDP_EGRESS */
>> + nla_total_size(4) /* IFLA_EVENT */
>> + nla_total_size(4) /* IFLA_NEW_NETNSID */
>> + nla_total_size(4) /* IFLA_NEW_IFINDEX */
>> @@ -1395,6 +1395,42 @@ static int rtnl_fill_link_ifmap(struct sk_buff *skb, struct net_device *dev)
>> return 0;
>> }
>>
>> +static u32 rtnl_xdp_egress_prog(struct net_device *dev)
>> +{
>> + const struct bpf_prog *prog;
>> +
>> + ASSERT_RTNL();
>> +
>> + prog = rtnl_dereference(dev->xdp_egress_prog);
>> + if (!prog)
>> + return 0;
>> + return prog->aux->id;
>> +}
>> +
>> +static int rtnl_xdp_egress_report(struct sk_buff *skb, struct net_device *dev,
>> + u32 *prog_id, u8 *mode, u8 tgt_mode, u32 attr,
>> + u32 (*get_prog_id)(struct net_device *dev))
>> +{
>> + u32 curr_id;
>> + int err;
>> +
>> + curr_id = get_prog_id(dev);
>> + if (!curr_id)
>> + return 0;
>> +
>> + *prog_id = curr_id;
>> + err = nla_put_u32(skb, attr, curr_id);
>> + if (err)
>> + return err;
>> +
>> + if (*mode != XDP_ATTACHED_NONE)
>> + *mode = XDP_ATTACHED_MULTI;
>> + else
>> + *mode = tgt_mode;
>> +
>> + return 0;
>> +}
>> +
>> static u32 rtnl_xdp_prog_skb(struct net_device *dev)
>> {
>> const struct bpf_prog *generic_xdp_prog;
>> @@ -1486,6 +1522,42 @@ static int rtnl_xdp_fill(struct sk_buff *skb, struct net_device *dev)
>> return err;
>> }
>>
>> +static int rtnl_xdp_egress_fill(struct sk_buff *skb, struct net_device *dev)
>> +{
>> + u8 mode = XDP_ATTACHED_NONE;
>> + struct nlattr *xdp;
>> + u32 prog_id = 0;
>> + int err;
>> +
>> + xdp = nla_nest_start_noflag(skb, IFLA_XDP_EGRESS);
>> + if (!xdp)
>> + return -EMSGSIZE;
>> +
>> + err = rtnl_xdp_egress_report(skb, dev, &prog_id, &mode,
>> + XDP_ATTACHED_EGRESS_CORE,
>> + IFLA_XDP_EGRESS_CORE_PROG_ID,
>> + rtnl_xdp_egress_prog);
>> + if (err)
>> + goto err_cancel;
>> +
>> + err = nla_put_u8(skb, IFLA_XDP_ATTACHED, mode);
>> + if (err)
>> + goto err_cancel;
>> +
>> + if (prog_id && mode != XDP_ATTACHED_MULTI) {
>> + err = nla_put_u32(skb, IFLA_XDP_PROG_ID, prog_id);
>> + if (err)
>> + goto err_cancel;
>> + }
>> +
>> + nla_nest_end(skb, xdp);
>> + return 0;
>> +
>> +err_cancel:
>> + nla_nest_cancel(skb, xdp);
>> + return err;
>> +}
>> +
>> static u32 rtnl_get_event(unsigned long event)
>> {
>> u32 rtnl_event_type = IFLA_EVENT_NONE;
>> @@ -1743,6 +1815,9 @@ static int rtnl_fill_ifinfo(struct sk_buff *skb,
>> if (rtnl_xdp_fill(skb, dev))
>> goto nla_put_failure;
>>
>> + if (rtnl_xdp_egress_fill(skb, dev))
>> + goto nla_put_failure;
>> +
>> if (dev->rtnl_link_ops || rtnl_have_link_slave_info(dev)) {
>> if (rtnl_link_fill(skb, dev) < 0)
>> goto nla_put_failure;
>> @@ -1827,6 +1902,7 @@ static const struct nla_policy ifla_policy[IFLA_MAX+1] = {
>> [IFLA_ALT_IFNAME] = { .type = NLA_STRING,
>> .len = ALTIFNAMSIZ - 1 },
>> [IFLA_PERM_ADDRESS] = { .type = NLA_REJECT },
>> + [IFLA_XDP_EGRESS] = { .type = NLA_NESTED },
>> };
>>
>> static const struct nla_policy ifla_info_policy[IFLA_INFO_MAX+1] = {
>> @@ -2482,7 +2558,8 @@ static int do_set_master(struct net_device *dev, int ifindex,
>> #define DO_SETLINK_NOTIFY 0x03
>>
>> static int do_setlink_xdp(struct net_device *dev, struct nlattr *tb,
>> - int *status, struct netlink_ext_ack *extack)
>> + int *status, bool egress,
>> + struct netlink_ext_ack *extack)
>> {
>> struct nlattr *xdp[IFLA_XDP_MAX + 1];
>> u32 xdp_flags = 0;
>> @@ -2498,6 +2575,10 @@ static int do_setlink_xdp(struct net_device *dev, struct nlattr *tb,
>>
>> if (xdp[IFLA_XDP_FLAGS]) {
>> xdp_flags = nla_get_u32(xdp[IFLA_XDP_FLAGS]);
>> + if (egress && xdp_flags & XDP_FLAGS_MODES) {
>> + NL_SET_ERR_MSG(extack, "XDP_FLAGS_MODES not valid for egress");
>> + goto out_einval;
>> + }
>> if (xdp_flags & ~XDP_FLAGS_MASK)
>> goto out_einval;
>> if (hweight32(xdp_flags & XDP_FLAGS_MODES) > 1)
>> @@ -2515,7 +2596,7 @@ static int do_setlink_xdp(struct net_device *dev, struct nlattr *tb,
>>
>> err = dev_change_xdp_fd(dev, extack,
>> nla_get_s32(xdp[IFLA_XDP_FD]),
>> - expected_fd, xdp_flags, false);
>> + expected_fd, xdp_flags, egress);
>> if (err)
>> return err;
>>
>> @@ -2821,7 +2902,14 @@ static int do_setlink(const struct sk_buff *skb,
>> }
>>
>> if (tb[IFLA_XDP]) {
>> - err = do_setlink_xdp(dev, tb[IFLA_XDP], &status, extack);
>> + err = do_setlink_xdp(dev, tb[IFLA_XDP], &status, false, extack);
>> + if (err)
>> + goto errout;
>> + }
>> +
>> + if (tb[IFLA_XDP_EGRESS]) {
>> + err = do_setlink_xdp(dev, tb[IFLA_XDP_EGRESS], &status, true,
>> + extack);
>> if (err)
>> goto errout;
>> }
>
> This means that IFLA_XDP and IFLA_XDP_EGRESS can be present in the same
> netlink message, right? But then installation of the RX program could
> succeed, but userspace would still get an error if the egress program
> installation fails? That is probably not good?
That's a good catch.
>
> Since I don't think we can atomically make sure both operations fail or
> succeed, maybe it's better to disallow both entries being present in the
> same netlink message?
>
I think so since there is no way to undo the setlink for IFLA_XDP if
IFLA_XDP_EGRESS fails - exisitng program references are gone.
Although, existing do_setlink leaves the device in an incomplete state
on any failure...
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