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bpf: cpumap xdp_buff to skb conversion and allocation

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This patch makes cpumap functional, by adding SKB allocation and
invoking the network stack on the dequeuing CPU.

For constructing the SKB on the remote CPU, the xdp_buff in converted
into a struct xdp_pkt, and it mapped into the top headroom of the
packet, to avoid allocating separate mem.  For now, struct xdp_pkt is
just a cpumap internal data structure, with info carried between
enqueue to dequeue.

If a driver doesn't have enough headroom it is simply dropped, with
return code -EOVERFLOW.  This will be picked up the xdp tracepoint
infrastructure, to allow users to catch this.

V2: take into account xdp->data_meta

V4:
 - Drop busypoll tricks, keeping it more simple.
 - Skip RPS and Generic-XDP-recursive-reinjection, suggested by Alexei

V5: correct RCU read protection around __netif_receive_skb_core.

V6: Setting TASK_RUNNING vs TASK_INTERRUPTIBLE based on talk with Rik van Riel

Signed-off-by: Jesper Dangaard Brouer <brouer@redhat.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
This commit is contained in:
Jesper Dangaard Brouer 2017-10-16 12:19:39 +02:00 committed by David S. Miller
parent 9c270af37b
commit 1c601d829a
3 changed files with 158 additions and 22 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

1
include/linux/netdevice.h
View File

@ -3260,6 +3260,7 @@ int do_xdp_generic(struct bpf_prog *xdp_prog, struct sk_buff *skb);
int netif_rx(struct sk_buff *skb);
int netif_rx_ni(struct sk_buff *skb);
int netif_receive_skb(struct sk_buff *skb);
int netif_receive_skb_core(struct sk_buff *skb);
gro_result_t napi_gro_receive(struct napi_struct *napi, struct sk_buff *skb);
void napi_gro_flush(struct napi_struct *napi, bool flush_old);
struct sk_buff *napi_get_frags(struct napi_struct *napi);

152
kernel/bpf/cpumap.c
View File

@ -25,6 +25,9 @@
#include <linux/kthread.h>
#include <linux/capability.h>
#include <linux/netdevice.h> /* netif_receive_skb_core */
#include <linux/etherdevice.h> /* eth_type_trans */
/* General idea: XDP packets getting XDP redirected to another CPU,
* will maximum be stored/queued for one driver ->poll() call. It is
* guaranteed that setting flush bit and flush operation happen on
@ -179,6 +182,92 @@ static void cpu_map_kthread_stop(struct work_struct *work)
kthread_stop(rcpu->kthread);
}
/* For now, xdp_pkt is a cpumap internal data structure, with info
* carried between enqueue to dequeue. It is mapped into the top
* headroom of the packet, to avoid allocating separate mem.
*/
struct xdp_pkt {
void *data;
u16 len;
u16 headroom;
u16 metasize;
struct net_device *dev_rx;
};
/* Convert xdp_buff to xdp_pkt */
static struct xdp_pkt *convert_to_xdp_pkt(struct xdp_buff *xdp)
{
struct xdp_pkt *xdp_pkt;
int metasize;
int headroom;
/* Assure headroom is available for storing info */
headroom = xdp->data - xdp->data_hard_start;
metasize = xdp->data - xdp->data_meta;
metasize = metasize > 0 ? metasize : 0;
if ((headroom - metasize) < sizeof(*xdp_pkt))
return NULL;
/* Store info in top of packet */
xdp_pkt = xdp->data_hard_start;
xdp_pkt->data = xdp->data;
xdp_pkt->len = xdp->data_end - xdp->data;
xdp_pkt->headroom = headroom - sizeof(*xdp_pkt);
xdp_pkt->metasize = metasize;
return xdp_pkt;
}
struct sk_buff *cpu_map_build_skb(struct bpf_cpu_map_entry *rcpu,
struct xdp_pkt *xdp_pkt)
{
unsigned int frame_size;
void *pkt_data_start;
struct sk_buff *skb;
/* build_skb need to place skb_shared_info after SKB end, and
* also want to know the memory "truesize". Thus, need to
* know the memory frame size backing xdp_buff.
*
* XDP was designed to have PAGE_SIZE frames, but this
* assumption is not longer true with ixgbe and i40e. It
* would be preferred to set frame_size to 2048 or 4096
* depending on the driver.
* frame_size = 2048;
* frame_len = frame_size - sizeof(*xdp_pkt);
*
* Instead, with info avail, skb_shared_info in placed after
* packet len. This, unfortunately fakes the truesize.
* Another disadvantage of this approach, the skb_shared_info
* is not at a fixed memory location, with mixed length
* packets, which is bad for cache-line hotness.
*/
frame_size = SKB_DATA_ALIGN(xdp_pkt->len) + xdp_pkt->headroom +
SKB_DATA_ALIGN(sizeof(struct skb_shared_info));
pkt_data_start = xdp_pkt->data - xdp_pkt->headroom;
skb = build_skb(pkt_data_start, frame_size);
if (!skb)
return NULL;
skb_reserve(skb, xdp_pkt->headroom);
__skb_put(skb, xdp_pkt->len);
if (xdp_pkt->metasize)
skb_metadata_set(skb, xdp_pkt->metasize);
/* Essential SKB info: protocol and skb->dev */
skb->protocol = eth_type_trans(skb, xdp_pkt->dev_rx);
/* Optional SKB info, currently missing:
* - HW checksum info (skb->ip_summed)
* - HW RX hash (skb_set_hash)
* - RX ring dev queue index (skb_record_rx_queue)
*/
return skb;
}
static int cpu_map_kthread_run(void *data)
{
struct bpf_cpu_map_entry *rcpu = data;
@ -191,15 +280,45 @@ static int cpu_map_kthread_run(void *data)
* kthread_stop signal until queue is empty.
*/
while (!kthread_should_stop() || !__ptr_ring_empty(rcpu->queue)) {
unsigned int processed = 0, drops = 0;
struct xdp_pkt *xdp_pkt;
schedule();
/* Do work */
while ((xdp_pkt = ptr_ring_consume(rcpu->queue))) {
/* For now just "refcnt-free" */
page_frag_free(xdp_pkt);
/* Release CPU reschedule checks */
if (__ptr_ring_empty(rcpu->queue)) {
__set_current_state(TASK_INTERRUPTIBLE);
schedule();
} else {
cond_resched();
}
__set_current_state(TASK_INTERRUPTIBLE);
__set_current_state(TASK_RUNNING);
/* Process packets in rcpu->queue */
local_bh_disable();
/*
* The bpf_cpu_map_entry is single consumer, with this
* kthread CPU pinned. Lockless access to ptr_ring
* consume side valid as no-resize allowed of queue.
*/
while ((xdp_pkt = __ptr_ring_consume(rcpu->queue))) {
struct sk_buff *skb;
int ret;
skb = cpu_map_build_skb(rcpu, xdp_pkt);
if (!skb) {
page_frag_free(xdp_pkt);
continue;
}
/* Inject into network stack */
ret = netif_receive_skb_core(skb);
if (ret == NET_RX_DROP)
drops++;
/* Limit BH-disable period */
if (++processed == 8)
break;
}
local_bh_enable(); /* resched point, may call do_softirq() */
}
__set_current_state(TASK_RUNNING);
@ -490,13 +609,6 @@ static int bq_flush_to_queue(struct bpf_cpu_map_entry *rcpu,
return 0;
}
/* Notice: Will change in later patch */
struct xdp_pkt {
void *data;
u16 len;
u16 headroom;
};
/* Runs under RCU-read-side, plus in softirq under NAPI protection.
* Thus, safe percpu variable access.
*/
@ -524,17 +636,13 @@ int cpu_map_enqueue(struct bpf_cpu_map_entry *rcpu, struct xdp_buff *xdp,
struct net_device *dev_rx)
{
struct xdp_pkt *xdp_pkt;
int headroom;
/* For now this is just used as a void pointer to data_hard_start.
* Followup patch will generalize this.
*/
xdp_pkt = xdp->data_hard_start;
xdp_pkt = convert_to_xdp_pkt(xdp);
if (!xdp_pkt)
return -EOVERFLOW;
/* Fake writing into xdp_pkt->data to measure overhead */
headroom = xdp->data - xdp->data_hard_start;
if (headroom < sizeof(*xdp_pkt))
xdp_pkt->data = xdp->data;
/* Info needed when constructing SKB on remote CPU */
xdp_pkt->dev_rx = dev_rx;
bq_enqueue(rcpu, xdp_pkt);
return 0;

27
net/core/dev.c
View File

@ -4492,6 +4492,33 @@ static int __netif_receive_skb_core(struct sk_buff *skb, bool pfmemalloc)
return ret;
}
/**
* netif_receive_skb_core - special purpose version of netif_receive_skb
* @skb: buffer to process
*
* More direct receive version of netif_receive_skb(). It should
* only be used by callers that have a need to skip RPS and Generic XDP.
* Caller must also take care of handling if (page_is_)pfmemalloc.
*
* This function may only be called from softirq context and interrupts
* should be enabled.
*
* Return values (usually ignored):
* NET_RX_SUCCESS: no congestion
* NET_RX_DROP: packet was dropped
*/
int netif_receive_skb_core(struct sk_buff *skb)
{
int ret;
rcu_read_lock();
ret = __netif_receive_skb_core(skb, false);
rcu_read_unlock();
return ret;
}
EXPORT_SYMBOL(netif_receive_skb_core);
static int __netif_receive_skb(struct sk_buff *skb)
{
int ret;