> -----Original Message----- > From: [email protected] > [mailto:[email protected]] On Behalf Of Jason Gunthorpe > Sent: Tuesday, July 14, 2015 3:42 PM > To: Steve Wise > Cc: 'Christoph Hellwig'; 'Sagi Grimberg'; 'Steve Wise'; 'Tom Talpey'; 'Doug > Ledford'; [email protected]; [email protected]; > [email protected]; [email protected]; [email protected]; > [email protected]; [email protected]; > [email protected]; [email protected]; 'Oren Duer' > Subject: Re: [PATCH V3 1/5] RDMA/core: Transport-independent access flags > > On Tue, Jul 14, 2015 at 02:58:23PM -0500, Steve Wise wrote: > > The local_dma_lkey can be used in any rdma sge that requires an > > lkey. > > No, this is where iWarp doesn't follow the generic API - a local dma > lkey cannot be used with iWarp's RDMA_READ WR lkey. In effect RDMA > READ requires an *rkey* (confusingly stuck into the lkey slot) for > iWarp. (Right?) >
Right, a local_dma_lkey is not an rkey, and iwarp requires the rkey for the read destination MR. Further that rkey needs REMOTE_WRITE. > *THAT* is really the core difference between IB and iWarp in this > area, not that the access flags are different. > It both. Because an rkey without REMOTE_WRITE would not work. > (cap_rmda_read_lkey_is_rkey ?) > IMO its more like rdma_cap_read_dest_needs_remote_write(). And maybe make it camel step too. ;) > > domain. But I claim for lkeys, the PD doesn't really protect > > anything since the remote peers can't use it anyway. > > I agree. > > To use a PD properly I'd have thought it should be created on a client > by client basis. The risk is tiny, but client X should not be able to > guess Y's RKey and then corrupt a data transfer. *Especially* on a > server if client X hasn't auth'd yet .... That is what the PD is for. > > > There is confusion about lkeys and rkeys with regard to iWARP. In > > the iWARP verbs, there is no distinction between an lkey and rkey: > > they are the same key, called a Steering Tag or STAG. When you > > create a MR, the lkey == rkey == STAG for iwarp transports. > > Somewhat related, but really a different issue, is that SGEs that > > are the target of a read need REMOTE_WRITE access flags on their > > STAG for iWARP. > > That is the clearest explanation for the iWarp difference I've seen so > far, thanks! > > Christoph: The take away from all this is that on iWarp RDMA_READ > requires a restricted temporary MR to provide the lkey value in the > WC. It cannot use local_dma_lkey. > > Everything else is the same between IB and iWarp: local_dma_lkey can > be used as the lkey for SEND, RECV, WRITE. > The source of a WRITE can use local_dma_lkey, not the destination. But this is true for IB and IW... -- To unsubscribe from this list: send the line "unsubscribe linux-rdma" in the body of a message to [email protected] More majordomo info at http://vger.kernel.org/majordomo-info.html
