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[119.244.79.106]) by smtp.gmail.com with ESMTPSA id 98e67ed59e1d1-30e11e33c2esm12871188a91.1.2025.05.23.08.38.45 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Fri, 23 May 2025 08:38:47 -0700 (PDT) Message-ID: <63702a66-4cc6-4562-89f4-857fe3f044e8@gmail.com> Date: Sat, 24 May 2025 00:38:43 +0900 Precedence: bulk X-Mailing-List: linux-rdma@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH] mm/hmm: Allow hmm_dma_map_alloc() to tolerate NULL device To: Christoph Hellwig Cc: linux-rdma@vger.kernel.org, linux-mm@kvack.org, leon@kernel.org, jgg@ziepe.ca, akpm@linux-foundation.org, jglisse@redhat.com, linux-kernel@vger.kernel.org, linux-pci@vger.kernel.org, zyjzyj2000@gmail.com References: <20250523143537.10362-1-dskmtsd@gmail.com> Content-Language: en-US From: Daisuke Matsuda In-Reply-To: Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit On 2025/05/23 23:48, Christoph Hellwig wrote: > On Fri, May 23, 2025 at 02:35:37PM +0000, Daisuke Matsuda wrote: >> Some drivers (such as rxe) may legitimately call hmm_dma_map_alloc() with a >> NULL device pointer, > > No, they may not. If something has no device with physical DMA > capabilities, it has not business calling into it. > Hi Christoph, RXE is a software emulator of IBTA RoCEv2, designed to allow systems equipped with standard Ethernet adapters to interoperate with other RoCEv2-capable nodes. Like other Infiniband subsystem drivers (under drivers/infiniband/{hw,sw}), RXE depends on the ib_core and ib_uverbs layers in drivers/infiniband/core. These common RDMA layers, in turn, rely on the HMM infrastructure for specific features such as On-Demand Paging. As a result, even though RXE lacks physical DMA capabilities, it still needs to interact with hmm_dma_map_alloc() through the shared RDMA core paths. This patch ensures that such software-only use cases do not trigger unintended null pointer dereferences. Thanks, Daisuke