netdev - Re: [PATCH v2 net 2/2] tg3: Fix data corruption on 5725 with TSO

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Date:	Mon, 13 May 2013 14:40:24 -0700
From:	Eric Dumazet <eric.dumazet@...il.com>
To:	Nithin Nayak Sujir <nsujir@...adcom.com>
Cc:	davem@...emloft.net, netdev@...r.kernel.org,
	Michael Chan <mchan@...adcom.com>, stable@...r.kernel.org
Subject: Re: [PATCH v2 net 2/2] tg3: Fix data corruption on 5725 with TSO

On Mon, 2013-05-13 at 14:34 -0700, Nithin Nayak Sujir wrote:
> 
> On 05/13/2013 02:14 PM, Eric Dumazet wrote:

> >> +/* Test for TSO DMA buffers that cross into regions which are within MSS bytes
> >> + * of any 4GB boundaries: 4G, 8G, etc
> >> + */
> >> +static inline int tg3_4g_tso_overflow_test(struct tg3 *tp, dma_addr_t mapping,
> >> +					   u32 len, u32 mss)
> >> +{
> >> +	if (tg3_asic_rev(tp) == ASIC_REV_5762 && mss) {
> >> +		u32 base = (u32) mapping & 0xffffffff;
> >> +
> >> +		return ((base + len + (mss & 0x3fff)) < base);
> >> +	}
> >> +	return 0;
> >> +}
> >> +
> >
> > I am curious : Does this condition even triggers ?
> >
> 
> Yes, it's a rare problem to occur and was reported in our lab. After we 
> implemented this fix, the problem didn't happen again.
> 

I just cant figure out which part of the kernel could allocate a
fragment spanning a 4G region.



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