From mboxrd@z Thu Jan 1 00:00:00 1970 From: Jason Gunthorpe Subject: Re: [PATCH V3 1/5] RDMA/core: Transport-independent access flags Date: Tue, 14 Jul 2015 14:41:45 -0600 Message-ID: <20150714204145.GC26927@obsidianresearch.com> References: <20150709000337.GE16812@obsidianresearch.com> <559EF332.7060103@redhat.com> <20150709225306.GA30741@obsidianresearch.com> <559FC710.1050307@talpey.com> <20150710161108.GA19042@obsidianresearch.com> <55A24571.60902@dev.mellanox.co.il> <00e201d0be6a$e49bc910$add35b30$@opengridcomputing.com> <20150714194512.GA25887@infradead.org> <00f901d0be6f$70c96b00$525c4100$@opengridcomputing.com> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Return-path: Content-Disposition: inline In-Reply-To: <00f901d0be6f$70c96b00$525c4100$@opengridcomputing.com> Sender: linux-nfs-owner-u79uwXL29TY76Z2rM5mHXA@public.gmane.org To: Steve Wise Cc: 'Christoph Hellwig' , 'Sagi Grimberg' , 'Steve Wise' , 'Tom Talpey' , 'Doug Ledford' , sagig-VPRAkNaXOzVWk0Htik3J/w@public.gmane.org, ogerlitz-VPRAkNaXOzVWk0Htik3J/w@public.gmane.org, roid-VPRAkNaXOzVWk0Htik3J/w@public.gmane.org, linux-rdma-u79uwXL29TY76Z2rM5mHXA@public.gmane.org, eli-VPRAkNaXOzVWk0Htik3J/w@public.gmane.org, target-devel-u79uwXL29TY76Z2rM5mHXA@public.gmane.org, linux-nfs-u79uwXL29TY76Z2rM5mHXA@public.gmane.org, trond.myklebust-7I+n7zu2hftEKMMhf/gKZA@public.gmane.org, bfields-uC3wQj2KruNg9hUCZPvPmw@public.gmane.org, 'Oren Duer' List-Id: linux-rdma@vger.kernel.org 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?) *THAT* is really the core difference between IB and iWarp in this area, not that the access flags are different. (cap_rmda_read_lkey_is_rkey ?) > 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. Jason -- To unsubscribe from this list: send the line "unsubscribe linux-nfs" in the body of a message to majordomo-u79uwXL29TY76Z2rM5mHXA@public.gmane.org More majordomo info at http://vger.kernel.org/majordomo-info.html