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Sun, 01 Feb 2026 22:04:53 -0800 (PST) Received: from twshared26871.17.frc2.facebook.com (2620:10d:c0a8:1b::30) by mail.thefacebook.com (2620:10d:c0a9:6f::8fd4) with Microsoft SMTP Server (version=TLS1_2, cipher=TLS_ECDHE_RSA_WITH_AES_128_GCM_SHA256) id 15.2.2562.35; Mon, 2 Feb 2026 06:04:49 +0000 Received: by devbig259.ftw1.facebook.com (Postfix, from userid 664516) id 9A6BBF963038; Sun, 1 Feb 2026 22:04:33 -0800 (PST) From: Zhiping Zhang To: Jason Gunthorpe CC: Leon Romanovsky , Bjorn Helgaas , , , , Keith Busch , Yochai Cohen , Yishai Hadas , Zhiping Zhang Subject: Re: [RFC 2/2] Set steering-tag directly for PCIe P2P memory access Date: Sun, 1 Feb 2026 22:04:30 -0800 Message-ID: <20260202060433.2341252-1-zhipingz@meta.com> X-Mailer: git-send-email 2.47.3 In-Reply-To: <20260128165739.GQ1641016@ziepe.ca> References: <20260128165739.GQ1641016@ziepe.ca> Precedence: bulk X-Mailing-List: netdev@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: quoted-printable X-FB-Internal: Safe X-Proofpoint-Spam-Details-Enc: AW1haW4tMjYwMjAyMDA1MSBTYWx0ZWRfXysBATjOfuAgx a7utI5zF4KaFoCRFBdW3Z7P+bFPZXHKCBU7vYTm6KA4bzf9Jh1iUE87jEWvtX3pWY/tDXrOIkwW mDMxdyLLdBfyggSyLrx0J6b6ZzJBXDmJ9csy53cS4Z50AmhGEaW0gZMnTGY6ZMBN+uz759DL/3t xL51r6FUGdgWCaoQqiCFm6Ca/8hGuqo6TypMbWz7caFpjiDjgJ3N2dZa/UoQfW/g7UUPsMg78U/ vRoyUGPgcWjrGMMWmR6ooOAeIr0NedHbpQrnZ7kJIEACYAxX+6MgqLmChUaLcBE/2OxQ98jgigm 9UWHxbgfnW0lNqRNCv+CvQo3tXZLYr+smtX4V1Ks1VmlO/46rXw1ftfxORIuaZDvbGIX5pcCzft efqdvnSLyL+BO3OVXagPJQLhDSzywEXzlPvpRR+VwWMpYfMGLr5s4/dQ2pyTsCURZrVBPplrmU5 3uTsNHWLdmTLjhmBmdg== X-Proofpoint-GUID: RzlDkgl1fjD1l-5meIo3qrz99p7oAsKQ X-Authority-Analysis: v=2.4 cv=F7Jat6hN c=1 sm=1 tr=0 ts=69803e85 cx=c_pps a=MfjaFnPeirRr97d5FC5oHw==:117 a=MfjaFnPeirRr97d5FC5oHw==:17 a=IkcTkHD0fZMA:10 a=HzLeVaNsDn8A:10 a=VkNPw1HP01LnGYTKEx00:22 a=NEAV23lmAAAA:8 a=VwQbUJbxAAAA:8 a=2NG-zBdR4ynPUO4DN4oA:9 a=QEXdDO2ut3YA:10 a=zZCYzV9kfG8A:10 X-Proofpoint-ORIG-GUID: RzlDkgl1fjD1l-5meIo3qrz99p7oAsKQ X-Proofpoint-Virus-Version: vendor=baseguard engine=ICAP:2.0.293,Aquarius:18.0.1121,Hydra:6.1.51,FMLib:17.12.100.49 definitions=2026-02-02_02,2026-01-30_04,2025-10-01_01 On Wed, 28 Jan 2026 12:57:39 -0400, Jason Gunthorpe wrote: > > Thanks Jason. > > > > We already have an end-to-end workflow around dmah (perftest =E2=86=92= rdma-core =E2=86=92 kernel) > > to carry the TPH hint, across multiple patch sets. References: > > https://github.com/linux-rdma/perftest/commit/98bfb3679a1e71ec96df6a= 6d6c8124ac66ebce25 > > https://github.com/linux-rdma/rdma-core/pull/1623/commits > > https://lore.kernel.org/all/cover.1752752567.git.leon@kernel.org/ > > > > Given that, I=E2=80=99d like to minimize churn and use the existing d= mah-based flow, while > > addressing the CPU-memory protection concern you raised. Would you be= open to > > reconsidering this approach? > > You would need to initialize the dmah from the dmabuf and then lock it > to only be usable with that dmabuf. It doesn't avoid any dmabuf work, > it just makes the whole flow more convoluted. > > Jason Thanks, I see your point. I=E2=80=99ll send a new revision that doesn=E2=80= =99t use dmah. Zhiping