Re: [PATCH v2 01/11] mm/migrate_device: Introduce migrate_pfn_from_page() helper

Balbir Singh
2026-01-09T22:48:45Z

On 1/7/26 19:18, Jordan Niethe wrote:
> To create a migrate from a given struct page, that page is first
> converted to its pfn, before passing the pfn to migrate_pfn().
>
> A future change will remove device private pages from the physical
> address space. This will mean that device private pages no longer have a
> pfn and must be handled separately.
>
> Prepare for this with a new helper:
>
> - migrate_pfn_from_page()
>
> This helper takes a struct page as parameter instead of a pfn. This will
> allow more flexibility for handling the mpfn differently for device
> private pages.
>
> Signed-off-by: Jordan Niethe <jniethe@nvidia.com>
> ---
> v2: New to series
> ---
> arch/powerpc/kvm/book3s_hv_uvmem.c | 2 +-
> drivers/gpu/drm/amd/amdkfd/kfd_migrate.c | 2 +-
> drivers/gpu/drm/drm_pagemap.c | 2 +-
> drivers/gpu/drm/nouveau/nouveau_dmem.c | 4 ++--
> include/linux/migrate.h | 5 +++++
> lib/test_hmm.c | 11 ++++++-----
> mm/migrate_device.c | 7 +++----
> 7 files changed, 19 insertions(+), 14 deletions(-)
>
> diff --git a/arch/powerpc/kvm/book3s_hv_uvmem.c b/arch/powerpc/kvm/book3s_hv_uvmem.c
> index e5000bef90f2..67910900af7b 100644
> --- a/arch/powerpc/kvm/book3s_hv_uvmem.c
> +++ b/arch/powerpc/kvm/book3s_hv_uvmem.c
> @@ -784,7 +784,7 @@ static int kvmppc_svm_page_in(struct vm_area_struct *vma,
> }
> }
>
> - *mig.dst = migrate_pfn(page_to_pfn(dpage));
> + *mig.dst = migrate_pfn_from_page(dpage);
> migrate_vma_pages(&mig);
> out_finalize:
> migrate_vma_finalize(&mig);
> diff --git a/drivers/gpu/drm/amd/amdkfd/kfd_migrate.c b/drivers/gpu/drm/amd/amdkfd/kfd_migrate.c
> index af53e796ea1b..ca552c34ece2 100644
> --- a/drivers/gpu/drm/amd/amdkfd/kfd_migrate.c
> +++ b/drivers/gpu/drm/amd/amdkfd/kfd_migrate.c
> @@ -646,7 +646,7 @@ svm_migrate_copy_to_ram(struct amdgpu_device *adev, struct svm_range *prange,
> pr_debug_ratelimited("dma mapping dst to 0x%llx, pfn 0x%lx\n",
> dst[i] >> PAGE_SHIFT, page_to_pfn(dpage));
>
> - migrate->dst[i] = migrate_pfn(page_to_pfn(dpage));
> + migrate->dst[i] = migrate_pfn_from_page(dpage);
> j++;
> }
>
> diff --git a/drivers/gpu/drm/drm_pagemap.c b/drivers/gpu/drm/drm_pagemap.c
> index 37d7cfbbb3e8..5ddf395847ef 100644
> --- a/drivers/gpu/drm/drm_pagemap.c
> +++ b/drivers/gpu/drm/drm_pagemap.c
> @@ -490,7 +490,7 @@ static int drm_pagemap_migrate_populate_ram_pfn(struct vm_area_struct *vas,
> goto free_pages;
>
> page = folio_page(folio, 0);
> - mpfn[i] = migrate_pfn(page_to_pfn(page));
> + mpfn[i] = migrate_pfn_from_page(page);
>
> next:
> if (page)
> diff --git a/drivers/gpu/drm/nouveau/nouveau_dmem.c b/drivers/gpu/drm/nouveau/nouveau_dmem.c
> index 58071652679d..a7edcdca9701 100644
> --- a/drivers/gpu/drm/nouveau/nouveau_dmem.c
> +++ b/drivers/gpu/drm/nouveau/nouveau_dmem.c
> @@ -249,7 +249,7 @@ static vm_fault_t nouveau_dmem_migrate_to_ram(struct vm_fault *vmf)
> goto done;
> }
>
> - args.dst[0] = migrate_pfn(page_to_pfn(dpage));
> + args.dst[0] = migrate_pfn_from_page(dpage);
> if (order)
> args.dst[0] |= MIGRATE_PFN_COMPOUND;
> dfolio = page_folio(dpage);
> @@ -766,7 +766,7 @@ static unsigned long nouveau_dmem_migrate_copy_one(struct nouveau_drm *drm,
> ((paddr >> PAGE_SHIFT) << NVIF_VMM_PFNMAP_V0_ADDR_SHIFT);
> if (src & MIGRATE_PFN_WRITE)
> *pfn |= NVIF_VMM_PFNMAP_V0_W;
> - mpfn = migrate_pfn(page_to_pfn(dpage));
> + mpfn = migrate_pfn_from_page(dpage);
> if (folio_order(page_folio(dpage)))
> mpfn |= MIGRATE_PFN_COMPOUND;
> return mpfn;
> diff --git a/include/linux/migrate.h b/include/linux/migrate.h
> index 26ca00c325d9..d269ec1400be 100644
> --- a/include/linux/migrate.h
> +++ b/include/linux/migrate.h
> @@ -140,6 +140,11 @@ static inline unsigned long migrate_pfn(unsigned long pfn)
> return (pfn << MIGRATE_PFN_SHIFT) | MIGRATE_PFN_VALID;
> }
>
> +static inline unsigned long migrate_pfn_from_page(struct page *page)
> +{
> + return migrate_pfn(page_to_pfn(page));
> +}
> +
> enum migrate_vma_direction {
> MIGRATE_VMA_SELECT_SYSTEM = 1 << 0,
> MIGRATE_VMA_SELECT_DEVICE_PRIVATE = 1 << 1,
> diff --git a/lib/test_hmm.c b/lib/test_hmm.c
> index 8af169d3873a..7e5248404d00 100644
> --- a/lib/test_hmm.c
> +++ b/lib/test_hmm.c
> @@ -727,7 +727,8 @@ static void dmirror_migrate_alloc_and_copy(struct migrate_vma *args,
> rpage = BACKING_PAGE(dpage);
> rpage->zone_device_data = dmirror;
>
> - *dst = migrate_pfn(page_to_pfn(dpage)) | write;
> + *dst = migrate_pfn_from_page(dpage) |
> + write;
> src_page = pfn_to_page(spfn + i);
>
> if (spage)
> @@ -754,7 +755,7 @@ static void dmirror_migrate_alloc_and_copy(struct migrate_vma *args,
> pr_debug("migrating from sys to dev pfn src: 0x%lx pfn dst: 0x%lx\n",
> page_to_pfn(spage), page_to_pfn(dpage));
>
> - *dst = migrate_pfn(page_to_pfn(dpage)) | write;
> + *dst = migrate_pfn_from_page(dpage) | write;
>
> if (is_large) {
> int i;
> @@ -989,7 +990,7 @@ static vm_fault_t dmirror_devmem_fault_alloc_and_copy(struct migrate_vma *args,
>
> if (dpage) {
> lock_page(dpage);
> - *dst |= migrate_pfn(page_to_pfn(dpage));
> + *dst |= migrate_pfn_from_page(dpage);
> }
>
> for (i = 0; i < (1 << order); i++) {
> @@ -1000,7 +1001,7 @@ static vm_fault_t dmirror_devmem_fault_alloc_and_copy(struct migrate_vma *args,
> if (!dpage && order) {
> dpage = alloc_page_vma(GFP_HIGHUSER_MOVABLE, args->vma, addr);
> lock_page(dpage);
> - dst[i] = migrate_pfn(page_to_pfn(dpage));
> + dst[i] = migrate_pfn_from_page(dpage);
> dst_page = pfn_to_page(page_to_pfn(dpage));
> dpage = NULL; /* For the next iteration */
> } else {
> @@ -1412,7 +1413,7 @@ static void dmirror_device_evict_chunk(struct dmirror_chunk *chunk)
>
> /* TODO Support splitting here */
> lock_page(dpage);
> - dst_pfns[i] = migrate_pfn(page_to_pfn(dpage));
> + dst_pfns[i] = migrate_pfn_from_page(dpage);
> if (src_pfns[i] & MIGRATE_PFN_WRITE)
> dst_pfns[i] |= MIGRATE_PFN_WRITE;
> if (order)
> diff --git a/mm/migrate_device.c b/mm/migrate_device.c
> index 23379663b1e1..1a2067f830da 100644
> --- a/mm/migrate_device.c
> +++ b/mm/migrate_device.c
> @@ -207,9 +207,8 @@ static int migrate_vma_collect_huge_pmd(pmd_t *pmdp, unsigned long start,
> .vma = walk->vma,
> };
>
> - unsigned long pfn = page_to_pfn(folio_page(folio, 0));
> -
> - migrate->src[migrate->npages] = migrate_pfn(pfn) | write
> + migrate->src[migrate->npages] = migrate_pfn_from_page(folio_page(folio, 0))
> + | write
> | MIGRATE_PFN_MIGRATE
> | MIGRATE_PFN_COMPOUND;
> migrate->dst[migrate->npages++] = 0;
> @@ -328,7 +327,7 @@ static int migrate_vma_collect_pmd(pmd_t *pmdp,
> goto again;
> }
>
> - mpfn = migrate_pfn(page_to_pfn(page)) |
> + mpfn = migrate_pfn_from_page(page) |
> MIGRATE_PFN_MIGRATE;
> if (softleaf_is_device_private_write(entry))
> mpfn |= MIGRATE_PFN_WRITE;

Makes sense

Reviewed-by: Balbir Singh <balbirs@nvidia.com>