Re: [PATCH v3 04/13] mm/migrate_device: Add migrate PFN flag to track device private pages

Kuehling, Felix
2026-01-28T05:09:49Z

On 2026-01-23 01:23, Jordan Niethe wrote:
> A future change will remove device private pages from the physical
> address space. This will mean that device private pages no longer have
> normal PFN and must be handled separately.
>
> Prepare for this by adding a MIGRATE_PFN_DEVICE_PRIVATE flag to indicate
> that a migrate pfn contains a PFN for a device private page.
>
> Signed-off-by: Jordan Niethe <jniethe@nvidia.com>
> Signed-off-by: Alistair Popple <apopple@nvidia.com>

Acked-by: Felix Kuehling <felix.kuehling@amd.com>

>
> ---
> v1:
> - Update for HMM huge page support
> - Update existing drivers to use MIGRATE_PFN_DEVICE
> v2:
> - Include changes to migrate_pfn_from_page()
> - Rename to MIGRATE_PFN_DEVICE_PRIVATE
> - drm/amd: Check adev->gmc.xgmi.connected_to_cpu
> - lib/test_hmm.c: Check chunk->pagemap.type == MEMORY_DEVICE_PRIVATE
>
> v3:
> - Use adev->kfd.pgmap.type == MEMORY_DEVICE_PRIVATE
> ---
> drivers/gpu/drm/amd/amdkfd/kfd_migrate.c | 7 ++++++-
> drivers/gpu/drm/nouveau/nouveau_dmem.c | 3 ++-
> drivers/gpu/drm/xe/xe_svm.c | 2 +-
> include/linux/migrate.h | 14 +++++++++-----
> lib/test_hmm.c | 6 +++++-
> 5 files changed, 23 insertions(+), 9 deletions(-)
>
> diff --git a/drivers/gpu/drm/amd/amdkfd/kfd_migrate.c b/drivers/gpu/drm/amd/amdkfd/kfd_migrate.c
> index 3dd7a35d19f7..5478e41877e5 100644
> --- a/drivers/gpu/drm/amd/amdkfd/kfd_migrate.c
> +++ b/drivers/gpu/drm/amd/amdkfd/kfd_migrate.c
> @@ -212,7 +212,12 @@ svm_migrate_copy_done(struct amdgpu_device *adev, struct dma_fence *mfence)
> unsigned long
> svm_migrate_addr_to_mpfn(struct amdgpu_device *adev, unsigned long addr)
> {
> - return migrate_pfn((addr + adev->kfd.pgmap.range.start) >> PAGE_SHIFT);
> + unsigned long flags = 0;
> +
> + if (adev->kfd.pgmap.type == MEMORY_DEVICE_PRIVATE)
> + flags |= MIGRATE_PFN_DEVICE_PRIVATE;
> + return migrate_pfn((addr + adev->kfd.pgmap.range.start) >> PAGE_SHIFT) |
> + flags;
> }
>
> static void
> diff --git a/drivers/gpu/drm/nouveau/nouveau_dmem.c b/drivers/gpu/drm/nouveau/nouveau_dmem.c
> index bd3f7102c3f9..adfa3df5cbc5 100644
> --- a/drivers/gpu/drm/nouveau/nouveau_dmem.c
> +++ b/drivers/gpu/drm/nouveau/nouveau_dmem.c
> @@ -484,7 +484,8 @@ nouveau_dmem_evict_chunk(struct nouveau_dmem_chunk *chunk)
> dma_info = kvcalloc(npages, sizeof(*dma_info), GFP_KERNEL | __GFP_NOFAIL);
>
> migrate_device_range(src_pfns,
> - migrate_pfn(chunk->pagemap.range.start >> PAGE_SHIFT),
> + migrate_pfn(chunk->pagemap.range.start >> PAGE_SHIFT) |
> + MIGRATE_PFN_DEVICE_PRIVATE,
> npages);
>
> for (i = 0; i < npages; i++) {
> diff --git a/drivers/gpu/drm/xe/xe_svm.c b/drivers/gpu/drm/xe/xe_svm.c
> index fbf5fd284616..a8aad9e0b1fb 100644
> --- a/drivers/gpu/drm/xe/xe_svm.c
> +++ b/drivers/gpu/drm/xe/xe_svm.c
> @@ -770,7 +770,7 @@ static int xe_svm_populate_devmem_mpfn(struct drm_pagemap_devmem *devmem_allocat
> int i;
>
> for (i = 0; i < drm_buddy_block_size(buddy, block) >> PAGE_SHIFT; ++i)
> - pfn[j++] = migrate_pfn(block_pfn + i);
> + pfn[j++] = migrate_pfn(block_pfn + i) | MIGRATE_PFN_DEVICE_PRIVATE;
> }
>
> return 0;
> diff --git a/include/linux/migrate.h b/include/linux/migrate.h
> index d269ec1400be..5fd2ee080bc0 100644
> --- a/include/linux/migrate.h
> +++ b/include/linux/migrate.h
> @@ -122,11 +122,12 @@ static inline int migrate_misplaced_folio(struct folio *folio, int node)
> * have enough bits to store all physical address and flags. So far we have
> * enough room for all our flags.
> */
> -#define MIGRATE_PFN_VALID (1UL << 0)
> -#define MIGRATE_PFN_MIGRATE (1UL << 1)
> -#define MIGRATE_PFN_WRITE (1UL << 3)
> -#define MIGRATE_PFN_COMPOUND (1UL << 4)
> -#define MIGRATE_PFN_SHIFT 6
> +#define MIGRATE_PFN_VALID (1UL << 0)
> +#define MIGRATE_PFN_MIGRATE (1UL << 1)
> +#define MIGRATE_PFN_WRITE (1UL << 3)
> +#define MIGRATE_PFN_COMPOUND (1UL << 4)
> +#define MIGRATE_PFN_DEVICE_PRIVATE (1UL << 5)
> +#define MIGRATE_PFN_SHIFT 6
>
> static inline struct page *migrate_pfn_to_page(unsigned long mpfn)
> {
> @@ -142,6 +143,9 @@ static inline unsigned long migrate_pfn(unsigned long pfn)
>
> static inline unsigned long migrate_pfn_from_page(struct page *page)
> {
> + if (is_device_private_page(page))
> + return migrate_pfn(page_to_pfn(page)) |
> + MIGRATE_PFN_DEVICE_PRIVATE;
> return migrate_pfn(page_to_pfn(page));
> }
>
> diff --git a/lib/test_hmm.c b/lib/test_hmm.c
> index a6ff292596f3..872d3846af7b 100644
> --- a/lib/test_hmm.c
> +++ b/lib/test_hmm.c
> @@ -1385,11 +1385,15 @@ static void dmirror_device_evict_chunk(struct dmirror_chunk *chunk)
> unsigned long *src_pfns;
> unsigned long *dst_pfns;
> unsigned int order = 0;
> + unsigned long flags = 0;
>
> src_pfns = kvcalloc(npages, sizeof(*src_pfns), GFP_KERNEL | __GFP_NOFAIL);
> dst_pfns = kvcalloc(npages, sizeof(*dst_pfns), GFP_KERNEL | __GFP_NOFAIL);
>
> - migrate_device_range(src_pfns, migrate_pfn(start_pfn), npages);
> + if (chunk->pagemap.type == MEMORY_DEVICE_PRIVATE)
> + flags |= MIGRATE_PFN_DEVICE_PRIVATE;
> +
> + migrate_device_range(src_pfns, migrate_pfn(start_pfn) | flags, npages);
> for (i = 0; i < npages; i++) {
> struct page *dpage, *spage;
>