Message-ID: <93b1a415-37a3-d495-b52f-cdc18a21ac74@intel.com>
Date:   Wed, 9 Oct 2019 09:32:47 -0700
From:   "Samudrala, Sridhar" <sridhar.samudrala@...el.com>
To:     Björn Töpel <bjorn.topel@...el.com>,
        magnus.karlsson@...el.com, netdev@...r.kernel.org,
        bpf@...r.kernel.org, intel-wired-lan@...ts.osuosl.org,
        maciej.fijalkowski@...el.com, tom.herbert@...el.com
Subject: Re: [PATCH bpf-next 2/4] xsk: allow AF_XDP sockets to receive packets
 directly from a queue

On 10/8/2019 1:05 AM, Björn Töpel wrote:
> On 2019-10-08 08:16, Sridhar Samudrala wrote:
>> Introduce a flag that can be specified during the bind() call
>> of an AF_XDP socket to receive packets directly from a queue when 
>> there is
>> no XDP program attached to the device.
>>
>> This is enabled by introducing a special BPF prog pointer called
>> BPF_PROG_DIRECT_XSK and a new bind flag XDP_DIRECT that can be specified
>> when binding an AF_XDP socket to a queue. At the time of bind(), an 
>> AF_XDP
>> socket in XDP_DIRECT mode, will attach BPF_PROG_DIRECT_XSK as a bpf 
>> program
>> if there is no other XDP program attached to the device. The device 
>> receive
>> queue is also associated with the AF_XDP socket.
>>
>> In the XDP receive path, if the bpf program is a DIRECT_XSK program, the
>> XDP buffer is passed to the AF_XDP socket that is associated with the
>> receive queue on which the packet is received.
>>
>> To avoid any overhead for nomal XDP programs, a static key is used to 
>> keep
>> a count of AF_XDP direct xsk sockets and static_branch_unlikely() is used
>> to handle receives for direct XDP sockets.
>>
>> Any attach of a normal XDP program will take precedence and the direct 
>> xsk
>> program will be removed. The direct XSK program will be attached
>> automatically when the normal XDP program is removed when there are any
>> AF_XDP direct sockets associated with that device.
>>
>> Signed-off-by: Sridhar Samudrala <sridhar.samudrala@...el.com>
>> ---
>>   include/linux/filter.h            | 18 ++++++++++++
>>   include/linux/netdevice.h         | 10 +++++++
>>   include/net/xdp_sock.h            |  5 ++++
>>   include/uapi/linux/if_xdp.h       |  5 ++++
>>   kernel/bpf/syscall.c              |  7 +++--
>>   net/core/dev.c                    | 50 
>> +++++++++++++++++++++++++++++++++
>>   net/core/filter.c                 | 58 
>> +++++++++++++++++++++++++++++++++++++++
>>   net/xdp/xsk.c                     | 51 
>> ++++++++++++++++++++++++++++++++--
>>   tools/include/uapi/linux/if_xdp.h |  5 ++++
>>   9 files changed, 204 insertions(+), 5 deletions(-)
>>
>> diff --git a/include/linux/filter.h b/include/linux/filter.h
>> index 2ce57645f3cd..db4ad85d8321 100644
>> --- a/include/linux/filter.h
>> +++ b/include/linux/filter.h
>> @@ -585,6 +585,9 @@ struct bpf_redirect_info {
>>       struct bpf_map *map;
>>       struct bpf_map *map_to_flush;
>>       u32 kern_flags;
>> +#ifdef CONFIG_XDP_SOCKETS
>> +    struct xdp_sock *xsk;
>> +#endif
>>   };
>>   DECLARE_PER_CPU(struct bpf_redirect_info, bpf_redirect_info);
>> @@ -693,6 +696,16 @@ static inline u32 bpf_prog_run_clear_cb(const 
>> struct bpf_prog *prog,
>>       return res;
>>   }
>> +#ifdef CONFIG_XDP_SOCKETS
>> +#define BPF_PROG_DIRECT_XSK    0x1
>> +#define bpf_is_direct_xsk_prog(prog) \
>> +    ((unsigned long)prog == BPF_PROG_DIRECT_XSK)
>> +DECLARE_STATIC_KEY_FALSE(xdp_direct_xsk_needed);
>> +u32 bpf_direct_xsk(const struct bpf_prog *prog, struct xdp_buff *xdp);
>> +#else
>> +#define bpf_is_direct_xsk_prog(prog) (false)
>> +#endif
>> +
>>   static __always_inline u32 bpf_prog_run_xdp(const struct bpf_prog 
>> *prog,
>>                           struct xdp_buff *xdp)
>>   {
>> @@ -702,6 +715,11 @@ static __always_inline u32 bpf_prog_run_xdp(const 
>> struct bpf_prog *prog,
>>        * already takes rcu_read_lock() when fetching the program, so
>>        * it's not necessary here anymore.
>>        */
>> +#ifdef CONFIG_XDP_SOCKETS
>> +    if (static_branch_unlikely(&xdp_direct_xsk_needed) &&
>> +        bpf_is_direct_xsk_prog(prog))
>> +        return bpf_direct_xsk(prog, xdp);
>> +#endif
>>       return BPF_PROG_RUN(prog, xdp);
>>   }
>> diff --git a/include/linux/netdevice.h b/include/linux/netdevice.h
>> index 48cc71aae466..f4d0f70aa718 100644
>> --- a/include/linux/netdevice.h
>> +++ b/include/linux/netdevice.h
>> @@ -743,6 +743,7 @@ struct netdev_rx_queue {
>>       struct xdp_rxq_info        xdp_rxq;
>>   #ifdef CONFIG_XDP_SOCKETS
>>       struct xdp_umem                 *umem;
>> +    struct xdp_sock            *xsk;
>>   #endif
>>   } ____cacheline_aligned_in_smp;
>> @@ -1836,6 +1837,10 @@ struct net_device {
>>       atomic_t        carrier_up_count;
>>       atomic_t        carrier_down_count;
>> +#ifdef CONFIG_XDP_SOCKETS
>> +    u16            direct_xsk_count;
> 
> Why u16? num_rx/tx_queues are unsigned ints.

OK. Will changes to unsigned int

> 
>> +#endif
>> +
>>   #ifdef CONFIG_WIRELESS_EXT
>>       const struct iw_handler_def *wireless_handlers;
>>       struct iw_public_data    *wireless_data;
>> @@ -3712,6 +3717,11 @@ int dev_forward_skb(struct net_device *dev, 
>> struct sk_buff *skb);
>>   bool is_skb_forwardable(const struct net_device *dev,
>>               const struct sk_buff *skb);
>> +#ifdef CONFIG_XDP_SOCKETS
>> +int dev_set_direct_xsk_prog(struct net_device *dev);
>> +int dev_clear_direct_xsk_prog(struct net_device *dev);
>> +#endif
>> +
>>   static __always_inline int ____dev_forward_skb(struct net_device *dev,
>>                              struct sk_buff *skb)
>>   {
>> diff --git a/include/net/xdp_sock.h b/include/net/xdp_sock.h
>> index c9398ce7960f..9158233d34e1 100644
>> --- a/include/net/xdp_sock.h
>> +++ b/include/net/xdp_sock.h
>> @@ -76,6 +76,9 @@ struct xsk_map_node {
>>       struct xdp_sock **map_entry;
>>   };
>> +/* Flags for the xdp_sock flags field. */
>> +#define XDP_SOCK_DIRECT (1 << 0)
>> +
>>   struct xdp_sock {
>>       /* struct sock must be the first member of struct xdp_sock */
>>       struct sock sk;
>> @@ -104,6 +107,7 @@ struct xdp_sock {
>>       struct list_head map_list;
>>       /* Protects map_list */
>>       spinlock_t map_list_lock;
>> +    u16 flags;
> 
> Right now only the XDP_DIRECT is tracked here. Maybe track all flags, 
> and show them in xsk_diag.

I see zc as the other field that can be converted into a flag.
Do you want to include that as part of this series or can it be done later?

> 
>>   };
>>   struct xdp_buff;
>> @@ -129,6 +133,7 @@ void xsk_set_tx_need_wakeup(struct xdp_umem *umem);
>>   void xsk_clear_rx_need_wakeup(struct xdp_umem *umem);
>>   void xsk_clear_tx_need_wakeup(struct xdp_umem *umem);
>>   bool xsk_umem_uses_need_wakeup(struct xdp_umem *umem);
>> +struct xdp_sock *xdp_get_xsk_from_qid(struct net_device *dev, u16 
>> queue_id);
>>   void xsk_map_try_sock_delete(struct xsk_map *map, struct xdp_sock *xs,
>>                    struct xdp_sock **map_entry);
>> diff --git a/include/uapi/linux/if_xdp.h b/include/uapi/linux/if_xdp.h
>> index be328c59389d..d202b5d40859 100644
>> --- a/include/uapi/linux/if_xdp.h
>> +++ b/include/uapi/linux/if_xdp.h
>> @@ -25,6 +25,11 @@
>>    * application.
>>    */
>>   #define XDP_USE_NEED_WAKEUP (1 << 3)
>> +/* This option allows an AF_XDP socket bound to a queue to receive all
>> + * the packets directly from that queue when there is no XDP program
>> + * attached to the device.
>> + */
>> +#define XDP_DIRECT    (1 << 4)
>>   /* Flags for xsk_umem_config flags */
>>   #define XDP_UMEM_UNALIGNED_CHUNK_FLAG (1 << 0)
>> diff --git a/kernel/bpf/syscall.c b/kernel/bpf/syscall.c
>> index 205f95af67d2..871d738a78d2 100644
>> --- a/kernel/bpf/syscall.c
>> +++ b/kernel/bpf/syscall.c
>> @@ -1349,13 +1349,14 @@ static void __bpf_prog_put(struct bpf_prog 
>> *prog, bool do_idr_lock)
>>   void bpf_prog_put(struct bpf_prog *prog)
>>   {
>> -    __bpf_prog_put(prog, true);
>> +    if (!bpf_is_direct_xsk_prog(prog))
>> +        __bpf_prog_put(prog, true);
>>   }
>>   EXPORT_SYMBOL_GPL(bpf_prog_put);
>>   u32 bpf_get_prog_id(const struct bpf_prog *prog)
>>   {
>> -    if (prog)
>> +    if (prog && !bpf_is_direct_xsk_prog(prog))
>>           return prog->aux->id;
>>       return 0;
>> @@ -1364,7 +1365,7 @@ EXPORT_SYMBOL(bpf_get_prog_id);
>>   void bpf_set_prog_id(struct bpf_prog *prog, u32 id)
>>   {
>> -    if (prog)
>> +    if (prog && !bpf_is_direct_xsk_prog(prog))
>>           prog->aux->id = id;
>>   }
>>   EXPORT_SYMBOL(bpf_set_prog_id);
>> diff --git a/net/core/dev.c b/net/core/dev.c
>> index 866d0ad936a5..eb3cd718e580 100644
>> --- a/net/core/dev.c
>> +++ b/net/core/dev.c
>> @@ -8269,6 +8269,10 @@ int dev_change_xdp_fd(struct net_device *dev, 
>> struct netlink_ext_ack *extack,
>>       } else {
>>           if (!__dev_xdp_query(dev, bpf_op, query))
>>               return 0;
>> +#ifdef CONFIG_XDP_SOCKETS
>> +        if (dev->direct_xsk_count)
>> +            prog = (void *)BPF_PROG_DIRECT_XSK;
>> +#endif
> 
> Nit, but maybe hide this weirdness in a function?

OK.

> 
>>       }
>>       err = dev_xdp_install(dev, bpf_op, extack, flags, prog);
>> @@ -8278,6 +8282,52 @@ int dev_change_xdp_fd(struct net_device *dev, 
>> struct netlink_ext_ack *extack,
>>       return err;
>>   }
>> +#ifdef CONFIG_XDP_SOCKETS
>> +int dev_set_direct_xsk_prog(struct net_device *dev)
>> +{
>> +    const struct net_device_ops *ops = dev->netdev_ops;
>> +    struct bpf_prog *prog;
>> +    bpf_op_t bpf_op;
>> +
>> +    ASSERT_RTNL();
>> +
>> +    dev->direct_xsk_count++;
>> +
>> +    bpf_op = ops->ndo_bpf;
>> +    if (!bpf_op)
>> +        return -EOPNOTSUPP;
>> +
>> +    if (__dev_xdp_query(dev, bpf_op, XDP_QUERY_PROG))
>> +        return 0;
>> +
>> +    prog = (void *)BPF_PROG_DIRECT_XSK;
>> +
>> +    return dev_xdp_install(dev, bpf_op, NULL, XDP_FLAGS_DRV_MODE, prog);
>> +}
>> +
>> +int dev_clear_direct_xsk_prog(struct net_device *dev)
>> +{
>> +    const struct net_device_ops *ops = dev->netdev_ops;
>> +    bpf_op_t bpf_op;
>> +
>> +    ASSERT_RTNL();
>> +
>> +    dev->direct_xsk_count--;
>> +
>> +    if (dev->direct_xsk_count)
>> +        return 0;
>> +
>> +    bpf_op = ops->ndo_bpf;
>> +    if (!bpf_op)
>> +        return -EOPNOTSUPP;
>> +
>> +    if (__dev_xdp_query(dev, bpf_op, XDP_QUERY_PROG))
>> +        return 0;
>> +
>> +    return dev_xdp_install(dev, bpf_op, NULL, XDP_FLAGS_DRV_MODE, NULL);
>> +}
>> +#endif
>> +
>>   /**
>>    *    dev_new_index    -    allocate an ifindex
>>    *    @net: the applicable net namespace
>> diff --git a/net/core/filter.c b/net/core/filter.c
>> index ed6563622ce3..391d7d600284 100644
>> --- a/net/core/filter.c
>> +++ b/net/core/filter.c
>> @@ -73,6 +73,7 @@
>>   #include <net/lwtunnel.h>
>>   #include <net/ipv6_stubs.h>
>>   #include <net/bpf_sk_storage.h>
>> +#include <linux/static_key.h>
>>   /**
>>    *    sk_filter_trim_cap - run a packet through a socket filter
>> @@ -3546,6 +3547,22 @@ static int __bpf_tx_xdp_map(struct net_device 
>> *dev_rx, void *fwd,
>>       return 0;
>>   }
>> +#ifdef CONFIG_XDP_SOCKETS
>> +static void xdp_do_flush_xsk(struct bpf_redirect_info *ri)
>> +{
>> +    struct xdp_sock *xsk = READ_ONCE(ri->xsk);
> 
> Why READ_ONCE here?
> 
>> +
>> +    if (xsk) {
>> +        ri->xsk = NULL;
>> +        xsk_flush(xsk);
>> +    }
>> +}
>> +#else
>> +static inline void xdp_do_flush_xsk(struct bpf_redirect_info *ri)
>> +{
>> +}
>> +#endif
>> +
> 
> Move CONFIG_XDP_SOCKETS into the function, and remove the empty/bottom one.
> 
>>   void xdp_do_flush_map(void)
>>   {
>>       struct bpf_redirect_info *ri = this_cpu_ptr(&bpf_redirect_info);
>> @@ -3568,6 +3585,8 @@ void xdp_do_flush_map(void)
>>               break;
>>           }
>>       }
>> +
>> +    xdp_do_flush_xsk(ri);
>>   }
>>   EXPORT_SYMBOL_GPL(xdp_do_flush_map);
>> @@ -3631,11 +3650,28 @@ static int xdp_do_redirect_map(struct 
>> net_device *dev, struct xdp_buff *xdp,
>>       return err;
>>   }
>> +#ifdef CONFIG_XDP_SOCKETS
>> +static inline struct xdp_sock *xdp_get_direct_xsk(struct 
>> bpf_redirect_info *ri)
>> +{
>> +    return READ_ONCE(ri->xsk);
> 
> Again, why READ_ONCE? Please leave the inlining to the compiler in .c 
> files.
> 
>> +}
>> +#else
>> +static inline struct xdp_sock *xdp_get_direct_xsk(struct 
>> bpf_redirect_info *ri)
>> +{
>> +    return NULL;
>> +}
>> +#endif
>> +
>>   int xdp_do_redirect(struct net_device *dev, struct xdp_buff *xdp,
>>               struct bpf_prog *xdp_prog)
>>   {
>>       struct bpf_redirect_info *ri = this_cpu_ptr(&bpf_redirect_info);
>>       struct bpf_map *map = READ_ONCE(ri->map);
>> +    struct xdp_sock *xsk;
>> +
>> +    xsk = xdp_get_direct_xsk(ri);
>> +    if (xsk)
>> +        return xsk_rcv(xsk, xdp);
> 
> Hmm, maybe you need a xsk_to_flush as well. Say that a user swaps in a
> regular XDP program, then xsk_rcv() will be called until the flush
> occurs, right? IOW, all packets processed (napi budget) in the napi_poll
> will end up in the socket.

I originally had xsk_to_flush considering this possibility of the XDP 
program changing before call to flush.
Will re-introduce it in the next revision.
Should i create a separate structure bpf_direct_xsk_info rather than 
adding these fields to bpf_redirect_info?


> 
>>       if (likely(map))
>>           return xdp_do_redirect_map(dev, xdp, xdp_prog, map, ri);
>> @@ -8934,4 +8970,26 @@ const struct bpf_verifier_ops 
>> sk_reuseport_verifier_ops = {
>>   const struct bpf_prog_ops sk_reuseport_prog_ops = {
>>   };
>> +
>> +#ifdef CONFIG_XDP_SOCKETS
>> +DEFINE_STATIC_KEY_FALSE(xdp_direct_xsk_needed);
>> +EXPORT_SYMBOL_GPL(xdp_direct_xsk_needed);
>> +
>> +u32 bpf_direct_xsk(const struct bpf_prog *prog, struct xdp_buff *xdp)
>> +{
>> +    struct xdp_sock *xsk;
>> +
>> +    xsk = xdp_get_xsk_from_qid(xdp->rxq->dev, xdp->rxq->queue_index);
>> +    if (xsk) {
>> +        struct bpf_redirect_info *ri = this_cpu_ptr(&bpf_redirect_info);
>> +
>> +        ri->xsk = xsk;
>> +        return XDP_REDIRECT;
> 
>  From the comment above. I *think* you need to ri->xsk_to_flush. Can the
> direct socket (swap socket) change before flush?

Yes.

> 
>> +    }
>> +
>> +    return XDP_PASS;
>> +}
>> +EXPORT_SYMBOL(bpf_direct_xsk);
>> +#endif
>> +
>>   #endif /* CONFIG_INET */
>> diff --git a/net/xdp/xsk.c b/net/xdp/xsk.c
>> index fa8fbb8fa3c8..8a29939bac7e 100644
>> --- a/net/xdp/xsk.c
>> +++ b/net/xdp/xsk.c
>> @@ -24,6 +24,7 @@
>>   #include <linux/rculist.h>
>>   #include <net/xdp_sock.h>
>>   #include <net/xdp.h>
>> +#include <linux/if_link.h>
>>   #include "xsk_queue.h"
>>   #include "xdp_umem.h"
>> @@ -264,6 +265,45 @@ int xsk_generic_rcv(struct xdp_sock *xs, struct 
>> xdp_buff *xdp)
>>       return err;
>>   }
>> +static void xdp_clear_direct_xsk(struct xdp_sock *xsk)
> 
> Use xs, and not xsk for consistency.

OK.

> 
>> +{
>> +    struct net_device *dev = xsk->dev;
>> +    u32 qid = xsk->queue_id;
>> +
>> +    if (!dev->_rx[qid].xsk)
>> +        return;
>> +
>> +    dev_clear_direct_xsk_prog(dev);
>> +    dev->_rx[qid].xsk = NULL;
>> +    static_branch_dec(&xdp_direct_xsk_needed);
>> +    xsk->flags &= ~XDP_SOCK_DIRECT;
>> +}
>> +
>> +static int xdp_set_direct_xsk(struct xdp_sock *xsk)
> 
> Same here.
> 
>> +{
>> +    struct net_device *dev = xsk->dev;
>> +    u32 qid = xsk->queue_id;
>> +    int err = 0;
>> +
>> +    if (dev->_rx[qid].xsk)
>> +        return -EEXIST;
>> +
>> +    xsk->flags |= XDP_SOCK_DIRECT;
>> +    static_branch_inc(&xdp_direct_xsk_needed);
>> +    dev->_rx[qid].xsk = xsk;
>> +    err = dev_set_direct_xsk_prog(dev);
>> +    if (err)
>> +        xdp_clear_direct_xsk(xsk);
>> +
>> +    return err;
>> +}
>> +
>> +struct xdp_sock *xdp_get_xsk_from_qid(struct net_device *dev, u16 
>> queue_id)
>> +{
>> +    return dev->_rx[queue_id].xsk;
>> +}
>> +EXPORT_SYMBOL(xdp_get_xsk_from_qid);
>> +
>>   void xsk_umem_complete_tx(struct xdp_umem *umem, u32 nb_entries)
>>   {
>>       xskq_produce_flush_addr_n(umem->cq, nb_entries);
>> @@ -464,6 +504,11 @@ static void xsk_unbind_dev(struct xdp_sock *xs)
>>           return;
>>       WRITE_ONCE(xs->state, XSK_UNBOUND);
>> +    if (xs->flags & XDP_SOCK_DIRECT) {
>> +        rtnl_lock();
>> +        xdp_clear_direct_xsk(xs);
>> +        rtnl_unlock();
>> +    }
>>       /* Wait for driver to stop using the xdp socket. */
>>       xdp_del_sk_umem(xs->umem, xs);
>>       xs->dev = NULL;
>> @@ -604,7 +649,7 @@ static int xsk_bind(struct socket *sock, struct 
>> sockaddr *addr, int addr_len)
>>       flags = sxdp->sxdp_flags;
>>       if (flags & ~(XDP_SHARED_UMEM | XDP_COPY | XDP_ZEROCOPY |
>> -              XDP_USE_NEED_WAKEUP))
>> +              XDP_USE_NEED_WAKEUP | XDP_DIRECT))
>>           return -EINVAL;
>>       rtnl_lock();
>> @@ -632,7 +677,7 @@ static int xsk_bind(struct socket *sock, struct 
>> sockaddr *addr, int addr_len)
>>           struct socket *sock;
>>           if ((flags & XDP_COPY) || (flags & XDP_ZEROCOPY) ||
>> -            (flags & XDP_USE_NEED_WAKEUP)) {
>> +            (flags & XDP_USE_NEED_WAKEUP) || (flags & XDP_DIRECT)) {
>>               /* Cannot specify flags for shared sockets. */
>>               err = -EINVAL;
>>               goto out_unlock;
>> @@ -688,6 +733,8 @@ static int xsk_bind(struct socket *sock, struct 
>> sockaddr *addr, int addr_len)
>>       xskq_set_umem(xs->rx, xs->umem->size, xs->umem->chunk_mask);
>>       xskq_set_umem(xs->tx, xs->umem->size, xs->umem->chunk_mask);
>>       xdp_add_sk_umem(xs->umem, xs);
>> +    if (flags & XDP_DIRECT)
>> +        err = xdp_set_direct_xsk(xs);
>>   out_unlock:
>>       if (err) {
>> diff --git a/tools/include/uapi/linux/if_xdp.h 
>> b/tools/include/uapi/linux/if_xdp.h
>> index be328c59389d..d202b5d40859 100644
>> --- a/tools/include/uapi/linux/if_xdp.h
>> +++ b/tools/include/uapi/linux/if_xdp.h
>> @@ -25,6 +25,11 @@
>>    * application.
>>    */
>>   #define XDP_USE_NEED_WAKEUP (1 << 3)
>> +/* This option allows an AF_XDP socket bound to a queue to receive all
>> + * the packets directly from that queue when there is no XDP program
>> + * attached to the device.
>> + */
>> +#define XDP_DIRECT    (1 << 4)
>>   /* Flags for xsk_umem_config flags */
>>   #define XDP_UMEM_UNALIGNED_CHUNK_FLAG (1 << 0)
>>

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