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v5 13/13] mm: Remove device private pages from the physical address space To: linux-mm@kvack.org, Matthew Brost Cc: balbirs@nvidia.com, matthew.brost@intel.com, akpm@linux-foundation.org, linux-kernel@vger.kernel.org, dri-devel@lists.freedesktop.org, david@redhat.com, ziy@nvidia.com, apopple@nvidia.com, lorenzo.stoakes@oracle.com, lyude@redhat.com, dakr@kernel.org, airlied@gmail.com, simona@ffwll.ch, rcampbell@nvidia.com, mpenttil@redhat.com, jgg@nvidia.com, willy@infradead.org, linuxppc-dev@lists.ozlabs.org, intel-xe@lists.freedesktop.org, jgg@ziepe.ca, Felix.Kuehling@amd.com, jhubbard@nvidia.com, maddy@linux.ibm.com, mpe@ellerman.id.au References: <20260130111050.53670-1-jniethe@nvidia.com> <20260130111050.53670-14-jniethe@nvidia.com> Content-Language: en-US From: Jordan Niethe In-Reply-To: <20260130111050.53670-14-jniethe@nvidia.com> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit X-ClientProxiedBy: SY8P300CA0019.AUSP300.PROD.OUTLOOK.COM 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 meNn+f9e 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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: Hi, On 30/1/26 22:10, Jordan Niethe wrote: > The existing design of device private memory imposes limitations which > render it non functional for certain systems and configurations where > the physical address space is limited. > > Device private memory is implemented by first reserving a region of the > physical address space. This is a problem. The physical address space is > not a resource that is directly under the kernel's control. Availability > of suitable physical address space is constrained by the underlying > hardware and firmware and may not always be available. > > Device private memory assumes that it will be able to reserve a device > memory sized chunk of physical address space. However, there is nothing > guaranteeing that this will succeed, and there a number of factors that > increase the likelihood of failure. We need to consider what else may > exist in the physical address space. It is observed that certain VM > configurations place very large PCI windows immediately after RAM. Large > enough that there is no physical address space available at all for > device private memory. This is more likely to occur on 43 bit physical > width systems which have less physical address space. > > Instead of using the physical address space, introduce a device private > address space and allocate devices regions from there to represent the > device private pages. > > Introduce a new interface memremap_device_private_pagemap() that > allocates a requested amount of device private address space and creates > the necessary device private pages. > > To support this new interface, struct dev_pagemap needs some changes: > > - Add a new dev_pagemap::nr_pages field as an input parameter. > - Add a new dev_pagemap::pages array to store the device > private pages. > > When using memremap_device_private_pagemap(), rather then passing in > dev_pagemap::ranges[dev_pagemap::nr_ranges] of physical address space to > be remapped, dev_pagemap::nr_ranges will always be 1, and the device > private range that is reserved is returned in dev_pagemap::range. > > Forbid calling memremap_pages() with dev_pagemap::ranges::type = > MEMORY_DEVICE_PRIVATE. > > Represent this device private address space using a new > device_private_pgmap_tree maple tree. This tree maps a given device > private address to a struct dev_pagemap, where a specific device private > page may then be looked up in that dev_pagemap::pages array. > > Device private address space can be reclaimed and the assoicated device > private pages freed using the corresponding new > memunmap_device_private_pagemap() interface. > > Because the device private pages now live outside the physical address > space, they no longer have a normal PFN. This means that page_to_pfn(), > et al. are no longer meaningful. > > Introduce helpers: > > - device_private_page_to_offset() > - device_private_folio_to_offset() > > to take a given device private page / folio and return its offset within > the device private address space. > > Update the places where we previously converted a device private page to > a PFN to use these new helpers. When we encounter a device private > offset, instead of looking up its page within the pagemap use > device_private_offset_to_page() instead. > > Update the existing users: > > - lib/test_hmm.c > - ppc ultravisor > - drm/amd/amdkfd > - gpu/drm/xe > - gpu/drm/nouveau > > to use the new memremap_device_private_pagemap() interface. > > Acked-by: Felix Kuehling > Reviewed-by: Zi Yan # for MM changes > Signed-off-by: Jordan Niethe > Signed-off-by: Alistair Popple > > --- Hi Matthew - the latest intel-xe CI run is passing: https://patchwork.freedesktop.org/series/159738/#rev8 Would you mind reviewing the gpu/drm/xe changes here and in: - [PATCH v5 01/13] mm/migrate_device: Introduce migrate_pfn_from_page() helper - [PATCH v5 03/13] mm/migrate_device: Make migrate_device_{pfns,range}() take mpfns - [PATCH v5 04/13] mm/migrate_device: Add migrate PFN flag to track device private pages Thanks very much, Jordan.