[Intel-wired-lan] [PATCH net v3] igb: cope with large MAX_SKB_FRAGS.

[Corinna Vinschen]

From: Paolo Abeni <pabeni at redhat.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 at redhat.com>
Reported-by: Jirka Hladky <jhladky at redhat.com>
Reported-by: Sabrina Dubroca <sd at queasysnail.net>
Tested-by: Sabrina Dubroca <sd at queasysnail.net>
Tested-by: Corinna Vinschen <vinschen at redhat.com>
Signed-off-by: Paolo Abeni <pabeni at redhat.com>
---
v2: fix subject, add a simple reproducer
v3: fix Fixes, tested with all MTUs from 1200 to 1280 per Eric's suggestion

 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
-- 
2.45.2