From: "Kulasek, TomaszX" <tomaszx.kulasek@intel.com>
To: "Richardson, Bruce" <bruce.richardson@intel.com>
Cc: "dev@dpdk.org" <dev@dpdk.org>,
"Zhang, Helin" <helin.zhang@intel.com>,
"Ananyev, Konstantin" <konstantin.ananyev@intel.com>
Subject: Re: [dpdk-dev] [PATCH] ixgbe: fix bad shift operation in ixgbe_set_pool_rx
Date: Fri, 22 Apr 2016 13:27:49 +0000 [thread overview]
Message-ID: <3042915272161B4EB253DA4D77EB373A14E9958F@IRSMSX102.ger.corp.intel.com> (raw)
In-Reply-To: <20160421152805.GA15560@bricha3-MOBL3>
> -----Original Message-----
> From: Richardson, Bruce
> Sent: Thursday, April 21, 2016 17:28
> To: Kulasek, TomaszX <tomaszx.kulasek@intel.com>
> Cc: dev@dpdk.org; Zhang, Helin <helin.zhang@intel.com>; Ananyev,
> Konstantin <konstantin.ananyev@intel.com>
> Subject: Re: [dpdk-dev] [PATCH] ixgbe: fix bad shift operation in
> ixgbe_set_pool_rx
>
> 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 <tomaszx.kulasek@intel.com>
> > > Cc: dev@dpdk.org; Zhang, Helin <helin.zhang@intel.com>; Ananyev,
> > > Konstantin <konstantin.ananyev@intel.com>
> > > 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 <tomaszx.kulasek@intel.com>
> > > > ---
> > > > 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 = IXGBE_VFRE(pool >= 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 value
> if pool > 63, but catching it doesn't solve a problem of possible overflow
> for pool > 31.
> >
> > > > reg = IXGBE_READ_REG(hw, addr);
> > > > - val = 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) == (bit1 << 1).
> > Pool value can be bigger than 31, and this is not an error while pool is
> 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.
>
> 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:
>
> /* for pool >= 32, set bit in PFVFRE[1], otherwise PFVFRE[0] */
> if (pool >= ETH_64_POOLS)
> return -EINVAL;
> else if (pool >= ETH_64_POOLS/2) {
> addr = IXGBE_VFRE(1);
> val = bit1 << (pool - 32);
> } else {
> addr = IXGBE_VFRE(0);
> val = bit1 << pool;
> }
>
> reg = IXGBE_READ_REG(hw, addr);
>
> This should fix the issue and make the resulting code clearer, I think.
>
> /Bruce
Yes, I got it. I will send v2.
Tomasz
next prev parent reply other threads:[~2016-04-22 13:29 UTC|newest]
Thread overview: 9+ messages / expand[flat|nested] mbox.gz Atom feed top
2016-04-15 13:39 Tomasz Kulasek
2016-04-18 1:57 ` Lu, Wenzhuo
2016-04-21 13:51 ` Bruce Richardson
2016-04-21 14:44 ` Kulasek, TomaszX
2016-04-21 15:28 ` Bruce Richardson
2016-04-22 13:27 ` Kulasek, TomaszX [this message]
2016-04-22 15:35 ` [dpdk-dev] [PATCH v2] ixgbe: fix bad shift operation in ixgbe_set_pool_rx/tx Tomasz Kulasek
2016-04-25 10:35 ` Bruce Richardson
2016-04-25 10:38 ` Bruce Richardson
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