netdev - Re: [PATCH v2] bnx2x: disable GSO where gso

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Date:   Mon, 15 Jan 2018 14:06:35 -0500 (EST)
From:   David Miller <davem@...emloft.net>
To:     dja@...ens.net
Cc:     netdev@...r.kernel.org, tlfalcon@...ux.vnet.ibm.com,
        Yuval.Mintz@...ium.com
Subject: Re: [PATCH v2] bnx2x: disable GSO where gso_size is too big for
 hardware

From: Daniel Axtens <dja@...ens.net>
Date: Fri, 12 Jan 2018 10:59:05 +1100

> If a bnx2x card is passed a GSO packet with a gso_size larger than
> ~9700 bytes, it will cause a firmware error that will bring the card
> down:
> 
> bnx2x: [bnx2x_attn_int_deasserted3:4323(enP24p1s0f0)]MC assert!
> bnx2x: [bnx2x_mc_assert:720(enP24p1s0f0)]XSTORM_ASSERT_LIST_INDEX 0x2
> bnx2x: [bnx2x_mc_assert:736(enP24p1s0f0)]XSTORM_ASSERT_INDEX 0x0 = 0x00000000 0x25e43e47 0x00463e01 0x00010052
> bnx2x: [bnx2x_mc_assert:750(enP24p1s0f0)]Chip Revision: everest3, FW Version: 7_13_1
> ... (dump of values continues) ...
> 
> Detect when gso_size + header length is greater than the maximum
> packet size (9700 bytes) and disable GSO. For simplicity and speed
> this is approximated by comparing gso_size against 9200 and assuming
> no-one will have more than 500 bytes of headers.

What is the MTU size configured on the bnx2x device when these 9700
byte packets are seen?

If it's less than 9700, whatever is allowing your device (openvswitch,
ibmveth, whatever) needs to be fixed.

I don't like this at all, quite frankly.  We'll have one device now that
has this special check, probably many others can run into this situation
as well but they won't be used on these kinds of powerpc boxes and
therefore nobody is going to notice.

I'm not applying this without more information or better justification,
sorry.