netdev - [PATCH net] igb: fix bit_shift to be in [1..8] range

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Message-Id: <20230516174146.2707152-1-anthony.l.nguyen@intel.com>
Date: Tue, 16 May 2023 10:41:46 -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: Aleksandr Loktionov <aleksandr.loktionov@...el.com>,
	anthony.l.nguyen@...el.com,
	jgarzik@...hat.com,
	Pucha Himasekhar Reddy <himasekharx.reddy.pucha@...el.com>
Subject: [PATCH net] igb: fix bit_shift to be in [1..8] range

From: Aleksandr Loktionov <aleksandr.loktionov@...el.com>

In igb_hash_mc_addr() the expression:
        "mc_addr[4] >> 8 - bit_shift", right shifting "mc_addr[4]"
shift by more than 7 bits always yields zero, so hash becomes not so different.
Add initialization with bit_shift = 1 and add a loop condition to ensure
bit_shift will be always in [1..8] range.

Fixes: 9d5c824399de ("igb: PCI-Express 82575 Gigabit Ethernet driver")
Signed-off-by: Aleksandr Loktionov <aleksandr.loktionov@...el.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>
---
 drivers/net/ethernet/intel/igb/e1000_mac.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/drivers/net/ethernet/intel/igb/e1000_mac.c b/drivers/net/ethernet/intel/igb/e1000_mac.c
index 205d577bdbba..caf91c6f52b4 100644
--- a/drivers/net/ethernet/intel/igb/e1000_mac.c
+++ b/drivers/net/ethernet/intel/igb/e1000_mac.c
@@ -426,7 +426,7 @@ void igb_mta_set(struct e1000_hw *hw, u32 hash_value)
 static u32 igb_hash_mc_addr(struct e1000_hw *hw, u8 *mc_addr)
 {
 	u32 hash_value, hash_mask;
-	u8 bit_shift = 0;
+	u8 bit_shift = 1;
 
 	/* Register count multiplied by bits per register */
 	hash_mask = (hw->mac.mta_reg_count * 32) - 1;
@@ -434,7 +434,7 @@ static u32 igb_hash_mc_addr(struct e1000_hw *hw, u8 *mc_addr)
 	/* For a mc_filter_type of 0, bit_shift is the number of left-shifts
 	 * where 0xFF would still fall within the hash mask.
 	 */
-	while (hash_mask >> bit_shift != 0xFF)
+	while (hash_mask >> bit_shift != 0xFF && bit_shift < 4)
 		bit_shift++;
 
 	/* The portion of the address that is used for the hash table
-- 
2.38.1