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Mon, 15 Sep 2025 09:30:03 -0700 (PDT) Received: from ziepe.ca ([130.41.10.202]) by smtp.gmail.com with ESMTPSA id 6a1803df08f44-781f4401f3bsm24381986d6.65.2025.09.15.09.30.02 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Mon, 15 Sep 2025 09:30:02 -0700 (PDT) Received: from jgg by wakko with local (Exim 4.97) (envelope-from ) id 1uyC5a-00000004TDO-10U1; Mon, 15 Sep 2025 13:30:02 -0300 Date: Mon, 15 Sep 2025 13:30:02 -0300 From: Jason Gunthorpe To: Parav Pandit Cc: Leon Romanovsky , Edward Srouji , "linux-rdma@vger.kernel.org" , "linux-kernel@vger.kernel.org" , Cosmin Ratiu , Vlad Dumitrescu , "kuba@kernel.org" , Tariq Toukan , Mark Bloch , Gal Pressman Subject: Re: [PATCH 2/4] RDMA/core: Resolve MAC of next-hop device without ARP support Message-ID: <20250915163002.GJ882933@ziepe.ca> References: <20250907160833.56589-1-edwards@nvidia.com> <20250907160833.56589-3-edwards@nvidia.com> <20250910083229.GK341237@unreal> Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: On Wed, Sep 10, 2025 at 10:55:36AM +0000, Parav Pandit wrote: > > > This leads to incorrect behavior and may result in packet transmission > > failures. > > > > > > Fix this by deferring MAC resolution to the IP stack via neighbour > > > lookup, allowing proper resolution or error reporting as appropriate. > > > > What is the difference here? For IPv4, neighbour lookup is ARP, no? > It is but it is not the only way. A device may not do ARP by itself but it relies on the rest of the stack like vrf or ip vlan mode to resolve. > A user may also set manual entry without explicit ARP. I think it was just a mistake to use NOARP this way in RDMA, I looked in the git history and there was no justification. That or it was right in the 2.x days and netdev moved on to the current schem. I expect to just call the neighbor functions and if they can't work for some reason they should fail? Jason