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[142.68.128.5]) by smtp.gmail.com with ESMTPSA id af79cd13be357-7b136164d89sm291152685a.3.2024.10.17.04.53.04 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Thu, 17 Oct 2024 04:53:04 -0700 (PDT) Received: from jgg by wakko with local (Exim 4.95) (envelope-from ) id 1t1P3w-003fyz-5b; Thu, 17 Oct 2024 08:53:04 -0300 Date: Thu, 17 Oct 2024 08:53:04 -0300 From: Jason Gunthorpe To: Alistair Popple Cc: Yonatan Maman , nouveau@lists.freedesktop.org, linux-kernel@vger.kernel.org, linux-rdma@vger.kernel.org, linux-mm@kvack.org, herbst@redhat.com, lyude@redhat.com, dakr@redhat.com, airlied@gmail.com, simona@ffwll.ch, leon@kernel.org, jglisse@redhat.com, akpm@linux-foundation.org, dri-devel@lists.freedesktop.org, bskeggs@nvidia.com, Gal Shalom Subject: Re: [PATCH v1 1/4] mm/hmm: HMM API for P2P DMA to device zone pages Message-ID: <20241017115304.GH4020792@ziepe.ca> References: <20241015152348.3055360-1-ymaman@nvidia.com> <20241015152348.3055360-2-ymaman@nvidia.com> <87frow8wdk.fsf@nvdebian.thelocal> <20241016154555.GE4020792@ziepe.ca> <878quno4os.fsf@nvdebian.thelocal> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <878quno4os.fsf@nvdebian.thelocal> X-Rspamd-Queue-Id: BDB19180011 X-Stat-Signature: o3n9imuc3kcggrsahehrfcsfaa8uea8n X-Rspamd-Server: rspam09 X-Rspam-User: X-HE-Tag: 1729165979-874316 X-HE-Meta: U2FsdGVkX1+nWdOS1b4hyxs3nsNw6Qr5tGnNC62UcZkJ7PDAVxHc0PzBTWt0gTvgG3k0bA1p3jquokhZ5XApFzB4EHaPSJ8mDyun/JcLJPATRu/Xa6M0HDsUjq2rEHJsmsnA8pBLfKNXjkaeeHZQikC5Ybc67nD+wS6p4CsNhVhSE+FtZaZF9EpNWFjpLpwCp0xpj2CZIYMDYP912j5iUDf+i9zmCdOpHobukmvNtTFIvL6uyo5OjGHTgQ4rmUpQ0MrEr95v78TN13iyBa+Hnm8P40kjNLDlsPE7d3KpbhRFlFMxUK6/FKpuVExCMYd88g4ZjcfTjL3n7SSC/BQl8TvKJA4RdVfmWH+GJ+wa4TZJYNXA5LxBIEbZWHaOfM8oiBVpinp65dyd7GKU1Ls9lnal2FEqKEBh5HEZSc4rU1J0od4lfLJynw5upsHF1bpo9jax4dNVZOv4eQbmghhNNSR18wKduM37RTpDt1TQEsimdwjrVdiuq49JIA67tyW+xkLK7C/RYUG4BB+40EzpCqbI9ly8Wc/LIEfK4U1UMfi4XT293wx6UcjSfzeqfRGuFe0EQgP7MM+eGVpwE+92rNhkXEpsJn8EfMUzwM1d90rdu8e4jr836lpAdYg/MOSGNsXLQE1NvnXwWStawO8j0j7ykMDoI4wmwE8Jknm6J5U26LOfpQtsV0++PhFiY8xU/Tkdq0aviuQdCAwRHqG5jOjM/aVEpIYPi+XqfJgVXfDm9l8xKbVYPbl7QCSBh45zzMD73wzIOgkZ1L0k6JBUUx8dMHYEWyr1xtpt6Z8dEXuG8+mPaKd8zPcmsmHy9Dcb1BuDwIC0vXCFRkQ8UsIwRTXzabSxG96Z/9wNQfscdTG3IXXN7/LpHXy8bE2aSeXogrM2op80k82ejsLhFqXneHOl81QUC4OOm2HX0c2Fx6U7R+Cvz0idFQUdoRalQq/MSBr15qdiEDuVli5e8ab kbwwxswt Nz7mWQZSvPzaw3yBqJL3BBFegk1OdJ8EzJ20b0CPjitHaE7o4Xb3ogADfPLKGdYnaQ+eV3f9ZBTpBlpMIHCi0uC1Pk29PztiC3B9JB7n6dwof5OHaye715rsYf3nrjAOuCqtLkUYboEsKNit5tRoiaSsCvpQO0Q3UH3WFLcZV0kwFGf+UZQR/W55aJSDrQMA4tLNZD4ho4bSEDoVq4WEv2FSb3vXzVAK7dEtCdq3HXNBW4kGrF6o+kaY88haWjjgAYTzZijbyJUKmdNJN7kNizwXM34JmLCO+eD1h X-Bogosity: Ham, tests=bogofilter, spamicity=0.000017, 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 Thu, Oct 17, 2024 at 12:58:48PM +1100, Alistair Popple wrote: > Actually I think the rule should be don't look at the page at > all. hmm_range_fault() is about mirroring PTEs, no assumption should > even be made about the existence or otherwise of a struct page. We are not there yet.. > > We don't need to enforce, it we don't know what else the driver will > > want to use that P2P page for after all. It might stick it in a VMA > > for some unrelated reason. > > And wouldn't that touch the refcount and therefore be wrong? I mean the originating driver would do that Jason