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.
regards,
dan carpenter
On Tue, Sep 18, 2012 at 10:34 AM, Dan Carpenter
[off-list ref] 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.
On Thu, Sep 20, 2012 at 04:46:51PM +0300, Or Gerlitz wrote:
On Tue, Sep 18, 2012 at 10:34 AM, Dan Carpenter
[off-list ref] wrote:
quoted
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.
Actually 24 bit big endian would mean they almost always over-write
the fence_size field. It's the highest byte of vlan_tag which would
not be modified.
I'm not sure how this ever worked. Something is confusing here.
regards,
dan carpenter