[PATCH net v3 2/2] igc: fix AF_XDP receive buffer size for 2K UMEM chunks

[Paul Moses <p@1g4.org>]

From: Maciej Fijalkowski <maciej.fijalkowski@intel.com>

SRRCTL.BSIZEPKT has a granularity of 1 KiB. With a 2 KiB UMEM
chunk and the default XDP headroom, xsk_pool_get_rx_frame_size()
returns 1792. Programming this value truncates the hardware receive
buffer size to 1 KiB, even though an MTU-sized frame fits in the
usable UMEM area.

XDP on igc is limited to MTU 1500, so configure a 2 KiB receive
buffer for XSK rings. Limit RLPML to the maximum supported Ethernet
frame size while XDP is attached, regardless of PAGE_SIZE, to avoid
oversized frames spanning descriptors or exceeding the usable UMEM
space.

RLPML is currently programmed from igc_set_rx_mode(), which can run
without RTNL, for example on an IPv6 multicast join, and could then
use a stale XDP state. RLPML does not depend on the address lists.
Program it from igc_setup_rctl() instead, next to RCTL.LPE, and from
igc_xdp_set_prog() while the rings are disabled. This avoids
netif_addr_lock_bh() usage.

Validate that the XSK frame size accommodates a maximum-size frame
with two VLAN tags, FCS and the optional inline RX timestamp. Check
against the maximum supported XDP MTU, rather than the current MTU,
which can change after the socket is bound.

Fixes: fc9df2a0b520 ("igc: Enable RX via AF_XDP zero-copy")
Signed-off-by: Maciej Fijalkowski <maciej.fijalkowski@intel.com>
Signed-off-by: Paul Moses <p@1g4.org>
---
 drivers/net/ethernet/intel/igc/igc.h      |  1 +
 drivers/net/ethernet/intel/igc/igc_main.c | 33 +++++++++++++++++------
 drivers/net/ethernet/intel/igc/igc_xdp.c  | 11 +++++---
 3 files changed, 33 insertions(+), 12 deletions(-)

diff --git a/drivers/net/ethernet/intel/igc/igc.h b/drivers/net/ethernet/intel/igc/igc.h
index 17f213cc9..ad1062f85 100644
--- a/drivers/net/ethernet/intel/igc/igc.h
+++ b/drivers/net/ethernet/intel/igc/igc.h
@@ -765,6 +765,7 @@ static inline s32 igc_read_phy_reg(struct igc_hw *hw, u32 offset, u16 *data)
 	return -EOPNOTSUPP;
 }
 
+void igc_set_rlpml(struct igc_adapter *adapter);
 void igc_reinit_locked(struct igc_adapter *);
 struct igc_nfc_rule *igc_get_nfc_rule(struct igc_adapter *adapter,
 				      u32 location);
diff --git a/drivers/net/ethernet/intel/igc/igc_main.c b/drivers/net/ethernet/intel/igc/igc_main.c
index 41b293dc1..6b418dc71 100644
--- a/drivers/net/ethernet/intel/igc/igc_main.c
+++ b/drivers/net/ethernet/intel/igc/igc_main.c
@@ -674,8 +674,11 @@ static void igc_configure_rx_ring(struct igc_adapter *adapter,
 	ring->next_to_clean = 0;
 	ring->next_to_use = 0;
 
+	/* igc's XDP limits MTU to 1500; all XSK RX buffers can use 2kb;
+	 * RLPML limits the receive length to fit after UMEM headroom.
+	 */
 	if (ring->xsk_pool)
-		buf_size = xsk_pool_get_rx_frame_size(ring->xsk_pool);
+		buf_size = IGC_RXBUFFER_2048;
 	else if (ring_uses_large_buffer(ring))
 		buf_size = IGC_RXBUFFER_3072;
 	else
@@ -830,6 +833,25 @@ static void igc_setup_mrqc(struct igc_adapter *adapter)
 	wr32(IGC_MRQC, mrqc);
 }
 
+void igc_set_rlpml(struct igc_adapter *adapter)
+{
+	struct igc_hw *hw = &adapter->hw;
+	u32 rlpml = MAX_JUMBO_FRAME_SIZE;
+
+#if (PAGE_SIZE < 8192)
+	if (adapter->max_frame_size <= IGC_MAX_FRAME_BUILD_SKB)
+		rlpml = IGC_MAX_FRAME_BUILD_SKB;
+#endif
+	/* igc's XDP currently does not support jumbo frames. Limit the
+	 * accepted packet size regardless of PAGE_SIZE so it fits in a 2kb
+	 * XSK chunk.
+	 */
+	if (igc_xdp_is_enabled(adapter))
+		rlpml = ETH_FRAME_LEN + VLAN_HLEN * 2 + ETH_FCS_LEN;
+
+	wr32(IGC_RLPML, rlpml);
+}
+
 /**
  * igc_setup_rctl - configure the receive control registers
  * @adapter: Board private structure
@@ -874,6 +896,7 @@ static void igc_setup_rctl(struct igc_adapter *adapter)
 			  IGC_RCTL_CFIEN); /* Disable VLAN CFIEN Filter */
 	}
 
+	igc_set_rlpml(adapter);
 	wr32(IGC_RCTL, rctl);
 }
 
@@ -4117,7 +4140,7 @@ static void igc_set_rx_mode(struct net_device *netdev)
 {
 	struct igc_adapter *adapter = netdev_priv(netdev);
 	struct igc_hw *hw = &adapter->hw;
-	u32 rctl = 0, rlpml = MAX_JUMBO_FRAME_SIZE;
+	u32 rctl = 0;
 	int count;
 
 	/* Check for Promiscuous and All Multicast modes */
@@ -4147,12 +4170,6 @@ static void igc_set_rx_mode(struct net_device *netdev)
 	/* update state of unicast and multicast */
 	rctl |= rd32(IGC_RCTL) & ~(IGC_RCTL_UPE | IGC_RCTL_MPE);
 	wr32(IGC_RCTL, rctl);
-
-#if (PAGE_SIZE < 8192)
-	if (adapter->max_frame_size <= IGC_MAX_FRAME_BUILD_SKB)
-		rlpml = IGC_MAX_FRAME_BUILD_SKB;
-#endif
-	wr32(IGC_RLPML, rlpml);
 }
 
 /**
diff --git a/drivers/net/ethernet/intel/igc/igc_xdp.c b/drivers/net/ethernet/intel/igc/igc_xdp.c
index 9eb47b4be..a0f1ecb2e 100644
--- a/drivers/net/ethernet/intel/igc/igc_xdp.c
+++ b/drivers/net/ethernet/intel/igc/igc_xdp.c
@@ -34,6 +34,8 @@ int igc_xdp_set_prog(struct igc_adapter *adapter, struct bpf_prog *prog,
 	}
 
 	old_prog = xchg(&adapter->xdp_prog, prog);
+	if (if_running && need_update)
+		igc_set_rlpml(adapter);
 	if (old_prog)
 		bpf_prog_put(old_prog);
 
@@ -69,11 +71,12 @@ static int igc_xdp_enable_pool(struct igc_adapter *adapter,
 		return -EINVAL;
 
 	frame_size = xsk_pool_get_rx_frame_size(pool);
-	if (frame_size < ETH_FRAME_LEN + VLAN_HLEN * 2) {
+	if (frame_size < ETH_FRAME_LEN + VLAN_HLEN * 2 +
+			 ETH_FCS_LEN + IGC_TS_HDR_LEN) {
 		/* When XDP is enabled, the driver doesn't support frames that
-		 * span over multiple buffers. To avoid that, we check if xsk
-		 * frame size is big enough to fit the max ethernet frame size
-		 * + vlan double tagging.
+		 * span multiple buffers. Check the maximum supported MTU, not
+		 * current MTU, as it may change while the pool is bound. Account
+		 * for double VLAN tags, FCS and inline RX timestamping.
 		 */
 		return -EOPNOTSUPP;
 	}
-- 
2.56.GIT