netdev - [PATCH net] igb: cope with large MAX_SKB

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Message-ID: <20240806221533.3360049-1-anthony.l.nguyen@intel.com>
Date: Tue,  6 Aug 2024 15:15:31 -0700
From: Tony Nguyen <anthony.l.nguyen@...el.com>
To: davem@...emloft.net,
	kuba@...nel.org,
	pabeni@...hat.com,
	edumazet@...gle.com,
	netdev@...r.kernel.org
Cc: anthony.l.nguyen@...el.com,
	Jan Tluka <jtluka@...hat.com>,
	Jirka Hladky <jhladky@...hat.com>,
	Sabrina Dubroca <sd@...asysnail.net>,
	Corinna Vinschen <vinschen@...hat.com>,
	Pucha Himasekhar Reddy <himasekharx.reddy.pucha@...el.com>
Subject: [PATCH net] igb: cope with large MAX_SKB_FRAGS.

From: Paolo Abeni <pabeni@...hat.com>

Sabrina reports that the igb driver does not cope well with large
MAX_SKB_FRAG values: setting MAX_SKB_FRAG to 45 causes payload
corruption on TX.

An easy reproducer is to run ssh to connect to the machine.  With
MAX_SKB_FRAGS=17 it works, with MAX_SKB_FRAGS=45 it fails.

The root cause of the issue is that the driver does not take into
account properly the (possibly large) shared info size when selecting
the ring layout, and will try to fit two packets inside the same 4K
page even when the 1st fraglist will trump over the 2nd head.

Address the issue forcing the driver to fit a single packet per page,
leaving there enough room to store the (currently) largest possible
skb_shared_info.

Fixes: 3948b05950fd ("net: introduce a config option to tweak MAX_SKB_FRAGS")
Reported-by: Jan Tluka <jtluka@...hat.com>
Reported-by: Jirka Hladky <jhladky@...hat.com>
Reported-by: Sabrina Dubroca <sd@...asysnail.net>
Tested-by: Sabrina Dubroca <sd@...asysnail.net>
Tested-by: Corinna Vinschen <vinschen@...hat.com>
Signed-off-by: Paolo Abeni <pabeni@...hat.com>
Reviewed-by: Eric Dumazet <edumazet@...gle.com>
Tested-by: Pucha Himasekhar Reddy <himasekharx.reddy.pucha@...el.com> (A Contingent worker at Intel)
Signed-off-by: Tony Nguyen <anthony.l.nguyen@...el.com>
---
iwl-net: https://lore.kernel.org/intel-wired-lan/20240718085633.1285322-1-vinschen@redhat.com/

 drivers/net/ethernet/intel/igb/igb_main.c | 1 +
 1 file changed, 1 insertion(+)

diff --git a/drivers/net/ethernet/intel/igb/igb_main.c b/drivers/net/ethernet/intel/igb/igb_main.c
index 11be39f435f3..232d6cb836a9 100644
--- a/drivers/net/ethernet/intel/igb/igb_main.c
+++ b/drivers/net/ethernet/intel/igb/igb_main.c
@@ -4808,6 +4808,7 @@ static void igb_set_rx_buffer_len(struct igb_adapter *adapter,
 
 #if (PAGE_SIZE < 8192)
 	if (adapter->max_frame_size > IGB_MAX_FRAME_BUILD_SKB ||
+	    SKB_HEAD_ALIGN(adapter->max_frame_size) > (PAGE_SIZE / 2) ||
 	    rd32(E1000_RCTL) & E1000_RCTL_SBP)
 		set_ring_uses_large_buffer(rx_ring);
 #endif
-- 
2.42.0