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[119.244.79.106]) by smtp.gmail.com with ESMTPSA id d9443c01a7336-231d4eba4bcsm125491825ad.182.2025.05.23.08.56.08 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Fri, 23 May 2025 08:56:10 -0700 (PDT) Message-ID: <56b45ad5-b3ae-40f2-bf3f-d0718e3d26c7@gmail.com> Date: Sat, 24 May 2025 00:56:07 +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> <63702a66-4cc6-4562-89f4-857fe3f044e8@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-Rspamd-Queue-Id: 5E67FC0009 X-Stat-Signature: e5h5oi4qajttqaxhqewgokdstpcj8j4w X-Rspam-User: X-Rspamd-Server: rspam04 X-HE-Tag: 1748015772-754077 X-HE-Meta: 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 deJWxjCT 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 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 2025/05/24 0:42, Christoph Hellwig wrote: > Thank you very much, but I know rxe very well. And given your apparent > knowledge of the rdma subsystem you should also know pretty well that > it does not otherwise call into the dma mapping core for virtual devices > because calling into the dma mapping code is not valid for the virtual > devices. > > Please fix the rdma core to not call into the hmm dma mapping helpers > for the ib_uses_virt_dma() case. > Thank you for the clarification and guidance. I'll look into updating the RDMA core to avoid calling hmm_dma_map_alloc() when ib_uses_virt_dma() is true. That should help keep the layering and responsibilities properly separated. Thanks again, Daisuke