From mboxrd@z Thu Jan 1 00:00:00 1970 From: "Kulasek, TomaszX" Subject: Re: [PATCH] ixgbe: fix bad shift operation in ixgbe_set_pool_rx Date: Fri, 22 Apr 2016 13:27:49 +0000 Message-ID: <3042915272161B4EB253DA4D77EB373A14E9958F@IRSMSX102.ger.corp.intel.com> References: <1460727549-4380-1-git-send-email-tomaszx.kulasek@intel.com> <20160421135134.GA15304@bricha3-MOBL3> <3042915272161B4EB253DA4D77EB373A14E992E8@IRSMSX102.ger.corp.intel.com> <20160421152805.GA15560@bricha3-MOBL3> Mime-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: quoted-printable Cc: "dev@dpdk.org" , "Zhang, Helin" , "Ananyev, Konstantin" To: "Richardson, Bruce" Return-path: Received: from mga09.intel.com (mga09.intel.com [134.134.136.24]) by dpdk.org (Postfix) with ESMTP id 053E22E8D for ; Fri, 22 Apr 2016 15:29:04 +0200 (CEST) In-Reply-To: <20160421152805.GA15560@bricha3-MOBL3> Content-Language: en-US List-Id: patches and discussions about DPDK List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Errors-To: dev-bounces@dpdk.org Sender: "dev" > -----Original Message----- > From: Richardson, Bruce > Sent: Thursday, April 21, 2016 17:28 > To: Kulasek, TomaszX > Cc: dev@dpdk.org; Zhang, Helin ; Ananyev, > Konstantin > Subject: Re: [dpdk-dev] [PATCH] ixgbe: fix bad shift operation in > ixgbe_set_pool_rx >=20 > On Thu, Apr 21, 2016 at 03:44:03PM +0100, Kulasek, TomaszX wrote: > > > > > > > -----Original Message----- > > > From: Richardson, Bruce > > > Sent: Thursday, April 21, 2016 15:52 > > > To: Kulasek, TomaszX > > > Cc: dev@dpdk.org; Zhang, Helin ; Ananyev, > > > Konstantin > > > Subject: Re: [dpdk-dev] [PATCH] ixgbe: fix bad shift operation in > > > ixgbe_set_pool_rx > > > > > > On Fri, Apr 15, 2016 at 03:39:09PM +0200, Tomasz Kulasek wrote: > > > > CID 13193 (#1 of 1): Bad bit shift operation (BAD_SHIFT) > > > > large_shift: In expression 1 << pool, left shifting by more than > > > > 31 bits has undefined behavior. The shift amount, pool, is at least > 32. > > > > > > > > This patch limits mask shift to be in range of 32 bit PFVFRE[1] > > > > register, for pool > 31. > > > > > > > > Fixes: fe3a45fd4104 ("ixgbe: add VMDq support") > > > > > > > > Signed-off-by: Tomasz Kulasek > > > > --- > > > > drivers/net/ixgbe/ixgbe_ethdev.c | 2 +- > > > > 1 file changed, 1 insertion(+), 1 deletion(-) > > > > > > > > diff --git a/drivers/net/ixgbe/ixgbe_ethdev.c > > > > b/drivers/net/ixgbe/ixgbe_ethdev.c > > > > index 3f1ebc1..f676a64 100644 > > > > --- a/drivers/net/ixgbe/ixgbe_ethdev.c > > > > +++ b/drivers/net/ixgbe/ixgbe_ethdev.c > > > > @@ -4401,7 +4401,7 @@ ixgbe_set_pool_rx(struct rte_eth_dev *dev, > > > > uint16_t pool, uint8_t on) > > > > > > > > addr =3D IXGBE_VFRE(pool >=3D ETH_64_POOLS/2); > > > > For pool in 0..31 PFVFRE[0] is used, for pool in 32..63, PFVFRE[1], but > for second case, we set/unset (pool-32) bit in the register. Invalid valu= e > if pool > 63, but catching it doesn't solve a problem of possible overflo= w > for pool > 31. > > > > > > reg =3D IXGBE_READ_REG(hw, addr); > > > > - val =3D bit1 << pool; > > > > Previous implementation expects that for shift operation will be used > rol on 32 bit value, and the bits that slide off the end of the register > are fed back into the spaces, eg. (bit1 << 33) =3D=3D (bit1 << 1). > > Pool value can be bigger than 31, and this is not an error while pool i= s > smaller than 64. > > > > Truncating pool value is clearer for me, than relay on obscure shift > operation. > > > Thanks for the explanation, that indeed does make it clearer. >=20 > However, all that detail is completely unclear to the reader of the > function, so perhaps we can clean up the code to make it more explicit > what is happening. > For example: >=20 > /* for pool >=3D 32, set bit in PFVFRE[1], otherwise PFVFRE[0] */ > if (pool >=3D ETH_64_POOLS) > return -EINVAL; > else if (pool >=3D ETH_64_POOLS/2) { > addr =3D IXGBE_VFRE(1); > val =3D bit1 << (pool - 32); > } else { > addr =3D IXGBE_VFRE(0); > val =3D bit1 << pool; > } >=20 > reg =3D IXGBE_READ_REG(hw, addr); >=20 > This should fix the issue and make the resulting code clearer, I think. >=20 > /Bruce Yes, I got it. I will send v2. Tomasz