netdev - [PATCH RFC v2 6/9] xdp: Add a flag for disabling napi_direct of xdp_return_frame in xdp_mem

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Message-Id: <20180610160217.3146-7-toshiaki.makita1@gmail.com>
Date:   Mon, 11 Jun 2018 01:02:14 +0900
From:   Toshiaki Makita <toshiaki.makita1@...il.com>
To:     netdev@...r.kernel.org
Cc:     Toshiaki Makita <makita.toshiaki@....ntt.co.jp>,
        Jesper Dangaard Brouer <brouer@...hat.com>,
        Alexei Starovoitov <ast@...nel.org>,
        Daniel Borkmann <daniel@...earbox.net>
Subject: [PATCH RFC v2 6/9] xdp: Add a flag for disabling napi_direct of xdp_return_frame in xdp_mem_info

From: Toshiaki Makita <makita.toshiaki@....ntt.co.jp>

We need some mechanism to disable napi_direct on calling
xdp_return_frame_rx_napi() from some context.
When veth gets support of XDP_REDIRECT, it will redirects packets which
are redirected from other devices. On redirection veth will reuse
xdp_mem_info of the redirection source device to make return_frame work.
But in this case .ndo_xdp_xmit() called from veth redirection uses
xdp_mem_info which is not guarded by NAPI, because the .ndo_xdp_xmit is
not called directly from the rxq which owns the xdp_mem_info.

This approach introduces a flag in xdp_mem_info to indicate that
napi_direct should be disabled even when _rx_napi variant is used.

Signed-off-by: Toshiaki Makita <makita.toshiaki@....ntt.co.jp>
---
 include/net/xdp.h | 4 ++++
 net/core/xdp.c    | 6 ++++--
 2 files changed, 8 insertions(+), 2 deletions(-)

diff --git a/include/net/xdp.h b/include/net/xdp.h
index 2deea7166a34..ea0c80f6c8ee 100644
--- a/include/net/xdp.h
+++ b/include/net/xdp.h
@@ -41,6 +41,9 @@ enum xdp_mem_type {
 	MEM_TYPE_MAX,
 };
 
+/* XDP flags for xdp_mem_info */
+#define XDP_MEM_RF_NO_DIRECT	BIT(0)	/* don't use napi_direct */
+
 /* XDP flags for ndo_xdp_xmit */
 #define XDP_XMIT_FLUSH		(1U << 0)	/* doorbell signal consumer */
 #define XDP_XMIT_FLAGS_MASK	XDP_XMIT_FLUSH
@@ -48,6 +51,7 @@ enum xdp_mem_type {
 struct xdp_mem_info {
 	u32 type; /* enum xdp_mem_type, but known size type */
 	u32 id;
+	u32 flags;
 };
 
 struct page_pool;
diff --git a/net/core/xdp.c b/net/core/xdp.c
index 9d1f22072d5d..e94f146360b2 100644
--- a/net/core/xdp.c
+++ b/net/core/xdp.c
@@ -327,10 +327,12 @@ static void __xdp_return(void *data, struct xdp_mem_info *mem, bool napi_direct,
 		/* mem->id is valid, checked in xdp_rxq_info_reg_mem_model() */
 		xa = rhashtable_lookup(mem_id_ht, &mem->id, mem_id_rht_params);
 		page = virt_to_head_page(data);
-		if (xa)
+		if (xa) {
+			napi_direct &= !(mem->flags & XDP_MEM_RF_NO_DIRECT);
 			page_pool_put_page(xa->page_pool, page, napi_direct);
-		else
+		} else {
 			put_page(page);
+		}
 		rcu_read_unlock();
 		break;
 	case MEM_TYPE_PAGE_SHARED:
-- 
2.14.3