veth: update mem type in xdp_buff

Veth calls skb_pp_cow_data() which makes the underlying memory to
originate from system page_pool. For CONFIG_DEBUG_VM=y and XDP program
that uses bpf_xdp_adjust_tail(), following splat was observed:

[   32.204881] BUG: Bad page state in process test_progs  pfn:11c98b
[   32.207167] page: refcount:0 mapcount:0 mapping:0000000000000000 index:0x0 pfn:0x11c98b
[   32.210084] flags: 0x1fffe0000000000(node=0|zone=1|lastcpupid=0x7fff)
[   32.212493] raw: 01fffe0000000000 dead000000000040 ff11000123c9b000 0000000000000000
[   32.218056] raw: 0000000000000000 0000000000000001 00000000ffffffff 0000000000000000
[   32.220900] page dumped because: page_pool leak
[   32.222636] Modules linked in: bpf_testmod(O) bpf_preload
[   32.224632] CPU: 6 UID: 0 PID: 3612 Comm: test_progs Tainted: G O        6.17.0-rc5-gfec474d29325 #6969 PREEMPT
[   32.224638] Tainted: [O]=OOT_MODULE
[   32.224639] Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS rel-1.14.0-0-g155821a1990b-prebuilt.qemu.org 04/01/2014
[   32.224641] Call Trace:
[   32.224644]  <IRQ>
[   32.224646]  dump_stack_lvl+0x4b/0x70
[   32.224653]  bad_page.cold+0xbd/0xe0
[   32.224657]  __free_frozen_pages+0x838/0x10b0
[   32.224660]  ? skb_pp_cow_data+0x782/0xc30
[   32.224665]  bpf_xdp_shrink_data+0x221/0x530
[   32.224668]  ? skb_pp_cow_data+0x6d1/0xc30
[   32.224671]  bpf_xdp_adjust_tail+0x598/0x810
[   32.224673]  ? xsk_destruct_skb+0x321/0x800
[   32.224678]  bpf_prog_004ac6bb21de57a7_xsk_xdp_adjust_tail+0x52/0xd6
[   32.224681]  veth_xdp_rcv_skb+0x45d/0x15a0
[   32.224684]  ? get_stack_info_noinstr+0x16/0xe0
[   32.224688]  ? veth_set_channels+0x920/0x920
[   32.224691]  ? get_stack_info+0x2f/0x80
[   32.224693]  ? unwind_next_frame+0x3af/0x1df0
[   32.224697]  veth_xdp_rcv.constprop.0+0x38a/0xbe0
[   32.224700]  ? common_startup_64+0x13e/0x148
[   32.224703]  ? veth_xdp_rcv_one+0xcd0/0xcd0
[   32.224706]  ? stack_trace_save+0x84/0xa0
[   32.224709]  ? stack_depot_save_flags+0x28/0x820
[   32.224713]  ? __resched_curr.constprop.0+0x332/0x3b0
[   32.224716]  ? timerqueue_add+0x217/0x320
[   32.224719]  veth_poll+0x115/0x5e0
[   32.224722]  ? veth_xdp_rcv.constprop.0+0xbe0/0xbe0
[   32.224726]  ? update_load_avg+0x1cb/0x12d0
[   32.224730]  ? update_cfs_group+0x121/0x2c0
[   32.224733]  __napi_poll+0xa0/0x420
[   32.224736]  net_rx_action+0x901/0xe90
[   32.224740]  ? run_backlog_napi+0x50/0x50
[   32.224743]  ? clockevents_program_event+0x1cc/0x280
[   32.224746]  ? hrtimer_interrupt+0x31e/0x7c0
[   32.224749]  handle_softirqs+0x151/0x430
[   32.224752]  do_softirq+0x3f/0x60
[   32.224755]  </IRQ>

It's because xdp_rxq with mem model set to MEM_TYPE_PAGE_SHARED was used
when initializing xdp_buff.

Fix this by using new helper xdp_convert_skb_to_buff() that, besides
init/prepare xdp_buff, will check if page used for linear part of
xdp_buff comes from page_pool. We assume that linear data and frags will
have same memory provider as currently XDP API does not provide us a way
to distinguish it (the mem model is registered for *whole* Rx queue and
here we speak about single buffer granularity).

In order to meet expected skb layout by new helper, pull the mac header
before conversion from skb to xdp_buff.

However, that is not enough as before releasing xdp_buff out of veth via
XDP_{TX,REDIRECT}, mem type on xdp_rxq associated with xdp_buff is
restored to its original model. We need to respect previous setting at
least until buff is converted to frame, as frame carries the mem_type.
Add a page_pool variant of veth_xdp_get() so that we avoid refcount
underflow when draining page frag.

Fixes: 0ebab78 ("net: veth: add page_pool for page recycling")
Reported-by: Alexei Starovoitov <[email protected]>
Closes: https://lore.kernel.org/bpf/CAADnVQ+bBofJDfieyOYzSmSujSfJwDTQhiz3aJw7hE+4E2_iPA@mail.gmail.com/
Signed-off-by: Maciej Fijalkowski <[email protected]>

Author: mfijalko

drivers/net/veth.c

@@ -733,7 +733,7 @@ static void veth_xdp_rcv_bulk_skb(struct veth_rq *rq, void **frames,
 	}
 }
 
-static void veth_xdp_get(struct xdp_buff *xdp)
+static void veth_xdp_get_shared(struct xdp_buff *xdp)
 {
 	struct skb_shared_info *sinfo = xdp_get_shared_info_from_buff(xdp);
 	int i;
@@ -746,12 +746,33 @@ static void veth_xdp_get(struct xdp_buff *xdp)
 		__skb_frag_ref(&sinfo->frags[i]);
 }
 
+static void veth_xdp_get_pp(struct xdp_buff *xdp)
+{
+	struct skb_shared_info *sinfo = xdp_get_shared_info_from_buff(xdp);
+	int i;
+
+	page_pool_ref_page(virt_to_page(xdp->data));
+	if (likely(!xdp_buff_has_frags(xdp)))
+		return;
+
+	for (i = 0; i < sinfo->nr_frags; i++) {
+		skb_frag_t *frag = &sinfo->frags[i];
+
+		page_pool_ref_page(netmem_to_page(frag->netmem));
+	}
+}
+
+static void veth_xdp_get(struct xdp_buff *xdp)
+{
+	xdp->rxq->mem.type == MEM_TYPE_PAGE_POOL ?
+		veth_xdp_get_pp(xdp) : veth_xdp_get_shared(xdp);
+}
+
 static int veth_convert_skb_to_xdp_buff(struct veth_rq *rq,
 					struct xdp_buff *xdp,
 					struct sk_buff **pskb)
 {
 	struct sk_buff *skb = *pskb;
-	u32 frame_sz;
 
 	if (skb_shared(skb) || skb_head_is_locked(skb) ||
 	    skb_shinfo(skb)->nr_frags ||
@@ -762,19 +783,9 @@ static int veth_convert_skb_to_xdp_buff(struct veth_rq *rq,
 		skb = *pskb;
 	}
 
-	/* SKB "head" area always have tailroom for skb_shared_info */
-	frame_sz = skb_end_pointer(skb) - skb->head;
-	frame_sz += SKB_DATA_ALIGN(sizeof(struct skb_shared_info));
-	xdp_init_buff(xdp, frame_sz, &rq->xdp_rxq);
-	xdp_prepare_buff(xdp, skb->head, skb_headroom(skb),
-			 skb_headlen(skb), true);
+	__skb_pull(*pskb, skb->data - skb_mac_header(skb));
 
-	if (skb_is_nonlinear(skb)) {
-		skb_shinfo(skb)->xdp_frags_size = skb->data_len;
-		xdp_buff_set_frags_flag(xdp);
-	} else {
-		xdp_buff_clear_frags_flag(xdp);
-	}
+	xdp_convert_skb_to_buff(skb, xdp, &rq->xdp_rxq);
 	*pskb = skb;
 
 	return 0;
@@ -822,24 +833,24 @@ static struct sk_buff *veth_xdp_rcv_skb(struct veth_rq *rq,
 	case XDP_TX:
 		veth_xdp_get(xdp);
 		consume_skb(skb);
-		xdp->rxq->mem = rq->xdp_mem;
 		if (unlikely(veth_xdp_tx(rq, xdp, bq) < 0)) {
 			trace_xdp_exception(rq->dev, xdp_prog, act);
 			stats->rx_drops++;
 			goto err_xdp;
 		}
 		stats->xdp_tx++;
+		rq->xdp_rxq.mem = rq->xdp_mem;
 		rcu_read_unlock();
 		goto xdp_xmit;
 	case XDP_REDIRECT:
 		veth_xdp_get(xdp);
 		consume_skb(skb);
-		xdp->rxq->mem = rq->xdp_mem;
 		if (xdp_do_redirect(rq->dev, xdp, xdp_prog)) {
 			stats->rx_drops++;
 			goto err_xdp;
 		}
 		stats->xdp_redirect++;
+		rq->xdp_rxq.mem = rq->xdp_mem;
 		rcu_read_unlock();
 		goto xdp_xmit;
 	default: