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

[Balbir Singh <balbirs@nvidia.com>]

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>