[ewg] Mellanox target workaround in SRP

[Vu Pham]

Roland Dreier wrote:
>  > I think that the patch is specific for srp initiator using Mellanox
>  > FMR. It tried to avoid indirect desc with Mellanox FMR having
>  > first-byte-offset != 0.  Since the low level implementation of
>  > mlx4/mthca_map_phys_fmr() did not create + setup MPT for FMR with
>  > first_byte_offset != 0. The corruption can happen with any target.
> 
> I don't think this could be right -- right now the workaround only
> triggers if the target has a Mellanox OUI, so if what you say is true,
> presumably everyone who is using the SRP initiator with mlx4 would be
> seeing this problem.

Yes, I'm afraid targets without Mellanox OUI would be seeing this problem.

> 
> Also, the SRP initiator code that uses ib_fmr_pool_map_phys does not
> pass in any non-aligned addresses -- it doesn't try to use any first
> byte offset, it just uses the virtual address it passes to the target to
> handle the offset.
> 


Yes and I suspect that the corruption happen with Mellanox FMR/MPT setup without fbo and target doing RDMA with offset vaddr.

Let me ask around and confirm.