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[142.167.56.70]) by smtp.gmail.com with ESMTPSA id 6a1803df08f44-7051b8c04fdsm8211446d6.15.2025.07.18.07.44.43 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Fri, 18 Jul 2025 07:44:43 -0700 (PDT) Received: from jgg by wakko with local (Exim 4.97) (envelope-from ) id 1ucmKI-00000009zcK-2UVK; Fri, 18 Jul 2025 11:44:42 -0300 Date: Fri, 18 Jul 2025 11:44:42 -0300 From: Jason Gunthorpe To: Matthew Wilcox Cc: Yonatan Maman , =?utf-8?B?SsOpcsO0bWU=?= Glisse , Andrew Morton , Leon Romanovsky , Lyude Paul , Danilo Krummrich , David Airlie , Simona Vetter , Alistair Popple , Ben Skeggs , Michael Guralnik , Or Har-Toov , Daisuke Matsuda , Shay Drory , linux-mm@kvack.org, linux-rdma@vger.kernel.org, dri-devel@lists.freedesktop.org, nouveau@lists.freedesktop.org, linux-kernel@vger.kernel.org, Gal Shalom Subject: Re: [PATCH v2 1/5] mm/hmm: HMM API to enable P2P DMA for device private pages Message-ID: <20250718144442.GG2206214@ziepe.ca> References: <20250718115112.3881129-1-ymaman@nvidia.com> <20250718115112.3881129-2-ymaman@nvidia.com> Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: On Fri, Jul 18, 2025 at 03:17:00PM +0100, Matthew Wilcox wrote: > On Fri, Jul 18, 2025 at 02:51:08PM +0300, Yonatan Maman wrote: > > +++ b/include/linux/memremap.h > > @@ -89,6 +89,14 @@ struct dev_pagemap_ops { > > */ > > vm_fault_t (*migrate_to_ram)(struct vm_fault *vmf); > > > > + /* > > + * Used for private (un-addressable) device memory only. Return a > > + * corresponding PFN for a page that can be mapped to device > > + * (e.g using dma_map_page) > > + */ > > + int (*get_dma_pfn_for_device)(struct page *private_page, > > + unsigned long *dma_pfn); > > This makes no sense. If a page is addressable then it has a PFN. > If a page is not addressable then it doesn't have a PFN. The DEVICE_PRIVATE pages have a PFN, but it is not usable for anything. This is effectively converting from a DEVICE_PRIVATE page to an actual DMA'able address of some kind. The DEVICE_PRIVATE is just a non-usable proxy, like a swap entry, for where the real data is sitting. Jason