Re: mlx4_en: fix endianness with blue frame support

Or Gerlitz
2012-09-20T13:46:52Z

On Tue, Sep 18, 2012 at 10:34 AM, Dan Carpenter
<dan.carpenter@oracle.com> wrote:
> Hello Thadeu Lima de Souza Cascardo,
>
> The patch c5d6136e10d6: "mlx4_en: fix endianness with blue frame
> support" from Oct 10, 2011, leads to the following warning:
> drivers/net/ethernet/mellanox/mlx4/en_tx.c:720 mlx4_en_xmit()
> warn: potential memory corrupting cast. 4 vs 2 bytes
>
> That patch introduced a call to cpu_to_be32() and added some endian notation.
> *(__be32 *) (&tx_desc->ctrl.vlan_tag) |= cpu_to_be32(ring->doorbell_qpn);
> But it doesn't make sense because the data type is declared as u16 in
> the header and we would be corrupting the next elements in the struct
> which are ins_vlan and fence_size.
>
> struct mlx4_wqe_ctrl_seg {
> __be32 owner_opcode;
> __be16 vlan_tag;
> u8 ins_vlan;
> u8 fence_size;
>
> I guess the reason we get away with it is that the ->doorbell_qpn is
> normally less that 65k. But doorbell_qpn is a u32 type so I think there is a risk here.

Dan,

QP numbers are 24 bit in size, under blue-flame setting the QP number
is written
over the "vlan_tag" field and potentially also the "ins_vlan" field of
the control segment,
we can do a little cleanup here with introducing a modified version of
the mlx4_wqe_ctrl_seg
structure over which the cast is made under the blue-flame flow.

Or.