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

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 <redacted>
---
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;