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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 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 X-Rspam-User: X-Rspamd-Queue-Id: 0E35E10000C X-Rspamd-Server: rspam09 X-Stat-Signature: r8fneqo6yccqihe7iai8tmj4egwudk9f X-HE-Tag: 1748014728-239023 X-HE-Meta: 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 WJ6IjiDO BSDMFExJPYpVYZhcuGu9V7mHBj0nI7QlDycqfHiemQG/T6KavTPBt7XnJnkvg4K3Spsu5eTi6hMXp+J+EOfkenyxxeNo8t2fBcrdhZtMHLRCqDN41I9Y9pGsnH4JnRAZaZ64YGNEdRNMxOwmlvRg7SJFIRrfGR/FmbhTg4fA4wLUalZ6uoLBPgfuOumHiIr8Ai8gbvWyOxZPm3ld+i2wXf8XyNN/FpdLXbQFXBc6RDMq+XQTKLpwTKH+T3DIjKxqAgXJFmd62T2X6qrUh+/wbytF6a3I+n7FRvVCT9yr5CDh8gU3EWwlybn4zlSB0JbtWeH2OCxTbFq+yh0ZdkFAqFip4kjrcbpzLAu3FOJf4qXFOYP43CY4dswedbREytfGE7wHV93zyR9oNvnbPm5N2eCqEZL+xdqRvJThrmfTqLKJwDoTmJo0UsVpBCT2P7m2k0A59o7KJU3RT7GnReOTONzY3qaMGsKvxZT23 X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: 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