thr3ads.net - Nouveau - [Nouveau] ensure device private pages have an owner [Mar 2020]

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Christoph Hellwig

2020-Mar-16 17:52 UTC

[Nouveau] ensure device private pages have an owner

When acting on device private mappings a driver needs to know if the
device (or other entity in case of kvmppc) actually owns this private
mapping.  This series adds an owner field and converts the migrate_vma
code over to check it.  I looked into doing the same for
hmm_range_fault, but as far as I can tell that code has never been
wired up to actually work for device private memory, so instead of
trying to fix some unused code the second patch just remove the code.
We can add it back once we have a working and fully tested code, and
then should pass the expected owner in the hmm_range structure.

Christoph Hellwig

2020-Mar-16 17:52 UTC

head link

[Nouveau] [PATCH 1/2] mm: handle multiple owners of device private pages in migrate_vma

Add a new opaque owner field to struct dev_pagemap, which will allow
the hmm and migrate_vma code to identify who owns ZONE_DEVICE memory,
and refuse to work on mappings not owned by the calling entity.

Signed-off-by: Christoph Hellwig <hch at lst.de>
---
 arch/powerpc/kvm/book3s_hv_uvmem.c     | 4 ++++
 drivers/gpu/drm/nouveau/nouveau_dmem.c | 3 +++
 include/linux/memremap.h               | 4 ++++
 include/linux/migrate.h                | 2 ++
 mm/migrate.c                           | 3 +++
 5 files changed, 16 insertions(+)

diff --git a/arch/powerpc/kvm/book3s_hv_uvmem.c
b/arch/powerpc/kvm/book3s_hv_uvmem.c
index 79b1202b1c62..29ed52892d31 100644
--- a/arch/powerpc/kvm/book3s_hv_uvmem.c
+++ b/arch/powerpc/kvm/book3s_hv_uvmem.c
@@ -386,6 +386,7 @@ kvmppc_svm_page_in(struct vm_area_struct *vma, unsigned long
start,
 	mig.end = end;
 	mig.src = &src_pfn;
 	mig.dst = &dst_pfn;
+	mig.dev_private_owner = &kvmppc_uvmem_pgmap;
 
 	/*
 	 * We come here with mmap_sem write lock held just for
@@ -563,6 +564,7 @@ kvmppc_svm_page_out(struct vm_area_struct *vma, unsigned
long start,
 	mig.end = end;
 	mig.src = &src_pfn;
 	mig.dst = &dst_pfn;
+	mig.dev_private_owner = &kvmppc_uvmem_pgmap;
 
 	mutex_lock(&kvm->arch.uvmem_lock);
 	/* The requested page is already paged-out, nothing to do */
@@ -779,6 +781,8 @@ int kvmppc_uvmem_init(void)
 	kvmppc_uvmem_pgmap.type = MEMORY_DEVICE_PRIVATE;
 	kvmppc_uvmem_pgmap.res = *res;
 	kvmppc_uvmem_pgmap.ops = &kvmppc_uvmem_ops;
+	/* just one global instance: */
+	kvmppc_uvmem_pgmap.owner = &kvmppc_uvmem_pgmap;
 	addr = memremap_pages(&kvmppc_uvmem_pgmap, NUMA_NO_NODE);
 	if (IS_ERR(addr)) {
 		ret = PTR_ERR(addr);
diff --git a/drivers/gpu/drm/nouveau/nouveau_dmem.c
b/drivers/gpu/drm/nouveau/nouveau_dmem.c
index 0ad5d87b5a8e..7605c4c48985 100644
--- a/drivers/gpu/drm/nouveau/nouveau_dmem.c
+++ b/drivers/gpu/drm/nouveau/nouveau_dmem.c
@@ -176,6 +176,7 @@ static vm_fault_t nouveau_dmem_migrate_to_ram(struct
vm_fault *vmf)
 		.end		= vmf->address + PAGE_SIZE,
 		.src		= &src,
 		.dst		= &dst,
+		.dev_private_owner = drm->dev,
 	};
 
 	/*
@@ -526,6 +527,7 @@ nouveau_dmem_init(struct nouveau_drm *drm)
 	drm->dmem->pagemap.type = MEMORY_DEVICE_PRIVATE;
 	drm->dmem->pagemap.res = *res;
 	drm->dmem->pagemap.ops = &nouveau_dmem_pagemap_ops;
+	drm->dmem->pagemap.owner = drm->dev;
 	if (IS_ERR(devm_memremap_pages(device, &drm->dmem->pagemap)))
 		goto out_free;
 
@@ -631,6 +633,7 @@ nouveau_dmem_migrate_vma(struct nouveau_drm *drm,
 	struct migrate_vma args = {
 		.vma		= vma,
 		.start		= start,
+		.dev_private_owner = drm->dev,
 	};
 	unsigned long c, i;
 	int ret = -ENOMEM;
diff --git a/include/linux/memremap.h b/include/linux/memremap.h
index 6fefb09af7c3..60d97e8fd3c0 100644
--- a/include/linux/memremap.h
+++ b/include/linux/memremap.h
@@ -103,6 +103,9 @@ struct dev_pagemap_ops {
  * @type: memory type: see MEMORY_* in memory_hotplug.h
  * @flags: PGMAP_* flags to specify defailed behavior
  * @ops: method table
+ * @owner: an opaque pointer identifying the entity that manages this
+ *	instance.  Used by various helpers to make sure that no
+ *	foreign ZONE_DEVICE memory is accessed.
  */
 struct dev_pagemap {
 	struct vmem_altmap altmap;
@@ -113,6 +116,7 @@ struct dev_pagemap {
 	enum memory_type type;
 	unsigned int flags;
 	const struct dev_pagemap_ops *ops;
+	void *owner;
 };
 
 static inline struct vmem_altmap *pgmap_altmap(struct dev_pagemap *pgmap)
diff --git a/include/linux/migrate.h b/include/linux/migrate.h
index 72120061b7d4..4bbd8d732e53 100644
--- a/include/linux/migrate.h
+++ b/include/linux/migrate.h
@@ -196,6 +196,8 @@ struct migrate_vma {
 	unsigned long		npages;
 	unsigned long		start;
 	unsigned long		end;
+
+	void			*dev_private_owner;
 };
 
 int migrate_vma_setup(struct migrate_vma *args);
diff --git a/mm/migrate.c b/mm/migrate.c
index b1092876e537..201e8fa627e0 100644
--- a/mm/migrate.c
+++ b/mm/migrate.c
@@ -2267,6 +2267,9 @@ static int migrate_vma_collect_pmd(pmd_t *pmdp,
 				goto next;
 
 			page = device_private_entry_to_page(entry);
+			if (page->pgmap->owner != migrate->dev_private_owner)
+				goto next;
+
 			mpfn = migrate_pfn(page_to_pfn(page)) |
 					MIGRATE_PFN_MIGRATE;
 			if (is_write_device_private_entry(entry))
-- 
2.24.1

Christoph Hellwig

2020-Mar-16 17:52 UTC

head link

[Nouveau] [PATCH 2/2] mm: remove device private page support from hmm_range_fault

No driver has actually used properly wire up and support this feature.
There is various code related to it in nouveau, but as far as I can tell
it never actually got turned on, and the only changes since the initial
commit are global cleanups.

Signed-off-by: Christoph Hellwig <hch at lst.de>
---
 drivers/gpu/drm/amd/amdgpu/amdgpu_ttm.c |  1 -
 drivers/gpu/drm/nouveau/nouveau_dmem.c  | 37 -------------------------
 drivers/gpu/drm/nouveau/nouveau_dmem.h  |  2 --
 drivers/gpu/drm/nouveau/nouveau_svm.c   |  3 --
 include/linux/hmm.h                     |  2 --
 mm/hmm.c                                | 28 -------------------
 6 files changed, 73 deletions(-)

diff --git a/drivers/gpu/drm/amd/amdgpu/amdgpu_ttm.c
b/drivers/gpu/drm/amd/amdgpu/amdgpu_ttm.c
index dee446278417..90821ce5e6ca 100644
--- a/drivers/gpu/drm/amd/amdgpu/amdgpu_ttm.c
+++ b/drivers/gpu/drm/amd/amdgpu/amdgpu_ttm.c
@@ -776,7 +776,6 @@ struct amdgpu_ttm_tt {
 static const uint64_t hmm_range_flags[HMM_PFN_FLAG_MAX] = {
 	(1 << 0), /* HMM_PFN_VALID */
 	(1 << 1), /* HMM_PFN_WRITE */
-	0 /* HMM_PFN_DEVICE_PRIVATE */
 };
 
 static const uint64_t hmm_range_values[HMM_PFN_VALUE_MAX] = {
diff --git a/drivers/gpu/drm/nouveau/nouveau_dmem.c
b/drivers/gpu/drm/nouveau/nouveau_dmem.c
index 7605c4c48985..42808efceaf2 100644
--- a/drivers/gpu/drm/nouveau/nouveau_dmem.c
+++ b/drivers/gpu/drm/nouveau/nouveau_dmem.c
@@ -671,40 +671,3 @@ nouveau_dmem_migrate_vma(struct nouveau_drm *drm,
 out:
 	return ret;
 }
-
-static inline bool
-nouveau_dmem_page(struct nouveau_drm *drm, struct page *page)
-{
-	return is_device_private_page(page) && drm->dmem ==
page_to_dmem(page);
-}
-
-void
-nouveau_dmem_convert_pfn(struct nouveau_drm *drm,
-			 struct hmm_range *range)
-{
-	unsigned long i, npages;
-
-	npages = (range->end - range->start) >> PAGE_SHIFT;
-	for (i = 0; i < npages; ++i) {
-		struct page *page;
-		uint64_t addr;
-
-		page = hmm_device_entry_to_page(range, range->pfns[i]);
-		if (page == NULL)
-			continue;
-
-		if (!(range->pfns[i] & range->flags[HMM_PFN_DEVICE_PRIVATE])) {
-			continue;
-		}
-
-		if (!nouveau_dmem_page(drm, page)) {
-			WARN(1, "Some unknown device memory !\n");
-			range->pfns[i] = 0;
-			continue;
-		}
-
-		addr = nouveau_dmem_page_addr(page);
-		range->pfns[i] &= ((1UL << range->pfn_shift) - 1);
-		range->pfns[i] |= (addr >> PAGE_SHIFT) << range->pfn_shift;
-	}
-}
diff --git a/drivers/gpu/drm/nouveau/nouveau_dmem.h
b/drivers/gpu/drm/nouveau/nouveau_dmem.h
index 92394be5d649..1ac620b3d4fb 100644
--- a/drivers/gpu/drm/nouveau/nouveau_dmem.h
+++ b/drivers/gpu/drm/nouveau/nouveau_dmem.h
@@ -38,8 +38,6 @@ int nouveau_dmem_migrate_vma(struct nouveau_drm *drm,
 			     unsigned long start,
 			     unsigned long end);
 
-void nouveau_dmem_convert_pfn(struct nouveau_drm *drm,
-			      struct hmm_range *range);
 #else /* IS_ENABLED(CONFIG_DRM_NOUVEAU_SVM) */
 static inline void nouveau_dmem_init(struct nouveau_drm *drm) {}
 static inline void nouveau_dmem_fini(struct nouveau_drm *drm) {}
diff --git a/drivers/gpu/drm/nouveau/nouveau_svm.c
b/drivers/gpu/drm/nouveau/nouveau_svm.c
index df9bf1fd1bc0..7e0376dca137 100644
--- a/drivers/gpu/drm/nouveau/nouveau_svm.c
+++ b/drivers/gpu/drm/nouveau/nouveau_svm.c
@@ -367,7 +367,6 @@ static const u64
 nouveau_svm_pfn_flags[HMM_PFN_FLAG_MAX] = {
 	[HMM_PFN_VALID         ] = NVIF_VMM_PFNMAP_V0_V,
 	[HMM_PFN_WRITE         ] = NVIF_VMM_PFNMAP_V0_W,
-	[HMM_PFN_DEVICE_PRIVATE] = NVIF_VMM_PFNMAP_V0_VRAM,
 };
 
 static const u64
@@ -558,8 +557,6 @@ static int nouveau_range_fault(struct nouveau_svmm *svmm,
 		break;
 	}
 
-	nouveau_dmem_convert_pfn(drm, &range);
-
 	svmm->vmm->vmm.object.client->super = true;
 	ret = nvif_object_ioctl(&svmm->vmm->vmm.object, data, size, NULL);
 	svmm->vmm->vmm.object.client->super = false;
diff --git a/include/linux/hmm.h b/include/linux/hmm.h
index 4bf8d6997b12..5e6034f105c3 100644
--- a/include/linux/hmm.h
+++ b/include/linux/hmm.h
@@ -74,7 +74,6 @@
  * Flags:
  * HMM_PFN_VALID: pfn is valid. It has, at least, read permission.
  * HMM_PFN_WRITE: CPU page table has write permission set
- * HMM_PFN_DEVICE_PRIVATE: private device memory (ZONE_DEVICE)
  *
  * The driver provides a flags array for mapping page protections to device
  * PTE bits. If the driver valid bit for an entry is bit 3,
@@ -86,7 +85,6 @@
 enum hmm_pfn_flag_e {
 	HMM_PFN_VALID = 0,
 	HMM_PFN_WRITE,
-	HMM_PFN_DEVICE_PRIVATE,
 	HMM_PFN_FLAG_MAX
 };
 
diff --git a/mm/hmm.c b/mm/hmm.c
index 180e398170b0..3d10485bf323 100644
--- a/mm/hmm.c
+++ b/mm/hmm.c
@@ -118,15 +118,6 @@ static inline void hmm_pte_need_fault(const struct
hmm_vma_walk *hmm_vma_walk,
 	/* We aren't ask to do anything ... */
 	if (!(pfns & range->flags[HMM_PFN_VALID]))
 		return;
-	/* If this is device memory then only fault if explicitly requested */
-	if ((cpu_flags & range->flags[HMM_PFN_DEVICE_PRIVATE])) {
-		/* Do we fault on device memory ? */
-		if (pfns & range->flags[HMM_PFN_DEVICE_PRIVATE]) {
-			*write_fault = pfns & range->flags[HMM_PFN_WRITE];
-			*fault = true;
-		}
-		return;
-	}
 
 	/* If CPU page table is not valid then we need to fault */
 	*fault = !(cpu_flags & range->flags[HMM_PFN_VALID]);
@@ -259,25 +250,6 @@ static int hmm_vma_handle_pte(struct mm_walk *walk,
unsigned long addr,
 	if (!pte_present(pte)) {
 		swp_entry_t entry = pte_to_swp_entry(pte);
 
-		/*
-		 * This is a special swap entry, ignore migration, use
-		 * device and report anything else as error.
-		 */
-		if (is_device_private_entry(entry)) {
-			cpu_flags = range->flags[HMM_PFN_VALID] |
-				range->flags[HMM_PFN_DEVICE_PRIVATE];
-			cpu_flags |= is_write_device_private_entry(entry) ?
-				range->flags[HMM_PFN_WRITE] : 0;
-			hmm_pte_need_fault(hmm_vma_walk, orig_pfn, cpu_flags,
-					   &fault, &write_fault);
-			if (fault || write_fault)
-				goto fault;
-			*pfn = hmm_device_entry_from_pfn(range,
-					    swp_offset(entry));
-			*pfn |= cpu_flags;
-			return 0;
-		}
-
 		hmm_pte_need_fault(hmm_vma_walk, orig_pfn, 0, &fault,
 				   &write_fault);
 		if (!fault && !write_fault)
-- 
2.24.1

Jason Gunthorpe

2020-Mar-16 18:17 UTC

head link

[Nouveau] [PATCH 1/2] mm: handle multiple owners of device private pages in migrate_vma

On Mon, Mar 16, 2020 at 06:52:58PM +0100, Christoph Hellwig
wrote:> Add a new opaque owner field to struct dev_pagemap, which will allow
> the hmm and migrate_vma code to identify who owns ZONE_DEVICE memory,
> and refuse to work on mappings not owned by the calling entity.
Using a pointer seems like a good solution to me.

Is this a bug fix? What is the downside for migrate on pages it
doesn't work? I'm not up to speed on migrate..

Jason

Ralph Campbell

2020-Mar-16 18:42 UTC

head link

[Nouveau] [PATCH 2/2] mm: remove device private page support from hmm_range_fault

On 3/16/20 10:52 AM, Christoph Hellwig wrote:> No driver has actually used properly wire up and support this feature.
> There is various code related to it in nouveau, but as far as I can tell
> it never actually got turned on, and the only changes since the initial
> commit are global cleanups.
This is not actually true. OpenCL 2.x does support SVM with nouveau and
device private memory via clEnqueueSVMMigrateMem().
Also, Ben Skeggs has accepted a set of patches to map GPU memory after being
migrated and this change would conflict with that.

> Signed-off-by: Christoph Hellwig <hch at lst.de>
> ---
>   drivers/gpu/drm/amd/amdgpu/amdgpu_ttm.c |  1 -
>   drivers/gpu/drm/nouveau/nouveau_dmem.c  | 37 -------------------------
>   drivers/gpu/drm/nouveau/nouveau_dmem.h  |  2 --
>   drivers/gpu/drm/nouveau/nouveau_svm.c   |  3 --
>   include/linux/hmm.h                     |  2 --
>   mm/hmm.c                                | 28 -------------------
>   6 files changed, 73 deletions(-)
> 
> diff --git a/drivers/gpu/drm/amd/amdgpu/amdgpu_ttm.c
b/drivers/gpu/drm/amd/amdgpu/amdgpu_ttm.c
> index dee446278417..90821ce5e6ca 100644
> --- a/drivers/gpu/drm/amd/amdgpu/amdgpu_ttm.c
> +++ b/drivers/gpu/drm/amd/amdgpu/amdgpu_ttm.c
> @@ -776,7 +776,6 @@ struct amdgpu_ttm_tt {
>   static const uint64_t hmm_range_flags[HMM_PFN_FLAG_MAX] = {
>   	(1 << 0), /* HMM_PFN_VALID */
>   	(1 << 1), /* HMM_PFN_WRITE */
> -	0 /* HMM_PFN_DEVICE_PRIVATE */
>   };
>   
>   static const uint64_t hmm_range_values[HMM_PFN_VALUE_MAX] = {
> diff --git a/drivers/gpu/drm/nouveau/nouveau_dmem.c
b/drivers/gpu/drm/nouveau/nouveau_dmem.c
> index 7605c4c48985..42808efceaf2 100644
> --- a/drivers/gpu/drm/nouveau/nouveau_dmem.c
> +++ b/drivers/gpu/drm/nouveau/nouveau_dmem.c
> @@ -671,40 +671,3 @@ nouveau_dmem_migrate_vma(struct nouveau_drm *drm,
>   out:
>   	return ret;
>   }
> -
> -static inline bool
> -nouveau_dmem_page(struct nouveau_drm *drm, struct page *page)
> -{
> -	return is_device_private_page(page) && drm->dmem ==
page_to_dmem(page);
> -}
> -
> -void
> -nouveau_dmem_convert_pfn(struct nouveau_drm *drm,
> -			 struct hmm_range *range)
> -{
> -	unsigned long i, npages;
> -
> -	npages = (range->end - range->start) >> PAGE_SHIFT;
> -	for (i = 0; i < npages; ++i) {
> -		struct page *page;
> -		uint64_t addr;
> -
> -		page = hmm_device_entry_to_page(range, range->pfns[i]);
> -		if (page == NULL)
> -			continue;
> -
> -		if (!(range->pfns[i] & range->flags[HMM_PFN_DEVICE_PRIVATE]))
{
> -			continue;
> -		}
> -
> -		if (!nouveau_dmem_page(drm, page)) {
> -			WARN(1, "Some unknown device memory !\n");
> -			range->pfns[i] = 0;
> -			continue;
> -		}
> -
> -		addr = nouveau_dmem_page_addr(page);
> -		range->pfns[i] &= ((1UL << range->pfn_shift) - 1);
> -		range->pfns[i] |= (addr >> PAGE_SHIFT) <<
range->pfn_shift;
> -	}
> -}
> diff --git a/drivers/gpu/drm/nouveau/nouveau_dmem.h
b/drivers/gpu/drm/nouveau/nouveau_dmem.h
> index 92394be5d649..1ac620b3d4fb 100644
> --- a/drivers/gpu/drm/nouveau/nouveau_dmem.h
> +++ b/drivers/gpu/drm/nouveau/nouveau_dmem.h
> @@ -38,8 +38,6 @@ int nouveau_dmem_migrate_vma(struct nouveau_drm *drm,
>   			     unsigned long start,
>   			     unsigned long end);
>   
> -void nouveau_dmem_convert_pfn(struct nouveau_drm *drm,
> -			      struct hmm_range *range);
>   #else /* IS_ENABLED(CONFIG_DRM_NOUVEAU_SVM) */
>   static inline void nouveau_dmem_init(struct nouveau_drm *drm) {}
>   static inline void nouveau_dmem_fini(struct nouveau_drm *drm) {}
> diff --git a/drivers/gpu/drm/nouveau/nouveau_svm.c
b/drivers/gpu/drm/nouveau/nouveau_svm.c
> index df9bf1fd1bc0..7e0376dca137 100644
> --- a/drivers/gpu/drm/nouveau/nouveau_svm.c
> +++ b/drivers/gpu/drm/nouveau/nouveau_svm.c
> @@ -367,7 +367,6 @@ static const u64
>   nouveau_svm_pfn_flags[HMM_PFN_FLAG_MAX] = {
>   	[HMM_PFN_VALID         ] = NVIF_VMM_PFNMAP_V0_V,
>   	[HMM_PFN_WRITE         ] = NVIF_VMM_PFNMAP_V0_W,
> -	[HMM_PFN_DEVICE_PRIVATE] = NVIF_VMM_PFNMAP_V0_VRAM,
>   };
>   
>   static const u64
> @@ -558,8 +557,6 @@ static int nouveau_range_fault(struct nouveau_svmm
*svmm,
>   		break;
>   	}
>   
> -	nouveau_dmem_convert_pfn(drm, &range);
> -
>   	svmm->vmm->vmm.object.client->super = true;
>   	ret = nvif_object_ioctl(&svmm->vmm->vmm.object, data, size,
NULL);
>   	svmm->vmm->vmm.object.client->super = false;
> diff --git a/include/linux/hmm.h b/include/linux/hmm.h
> index 4bf8d6997b12..5e6034f105c3 100644
> --- a/include/linux/hmm.h
> +++ b/include/linux/hmm.h
> @@ -74,7 +74,6 @@
>    * Flags:
>    * HMM_PFN_VALID: pfn is valid. It has, at least, read permission.
>    * HMM_PFN_WRITE: CPU page table has write permission set
> - * HMM_PFN_DEVICE_PRIVATE: private device memory (ZONE_DEVICE)
>    *
>    * The driver provides a flags array for mapping page protections to
device
>    * PTE bits. If the driver valid bit for an entry is bit 3,
> @@ -86,7 +85,6 @@
>   enum hmm_pfn_flag_e {
>   	HMM_PFN_VALID = 0,
>   	HMM_PFN_WRITE,
> -	HMM_PFN_DEVICE_PRIVATE,
>   	HMM_PFN_FLAG_MAX
>   };
>   
> diff --git a/mm/hmm.c b/mm/hmm.c
> index 180e398170b0..3d10485bf323 100644
> --- a/mm/hmm.c
> +++ b/mm/hmm.c
> @@ -118,15 +118,6 @@ static inline void hmm_pte_need_fault(const struct
hmm_vma_walk *hmm_vma_walk,
>   	/* We aren't ask to do anything ... */
>   	if (!(pfns & range->flags[HMM_PFN_VALID]))
>   		return;
> -	/* If this is device memory then only fault if explicitly requested */
> -	if ((cpu_flags & range->flags[HMM_PFN_DEVICE_PRIVATE])) {
> -		/* Do we fault on device memory ? */
> -		if (pfns & range->flags[HMM_PFN_DEVICE_PRIVATE]) {
> -			*write_fault = pfns & range->flags[HMM_PFN_WRITE];
> -			*fault = true;
> -		}
> -		return;
> -	}
>   
>   	/* If CPU page table is not valid then we need to fault */
>   	*fault = !(cpu_flags & range->flags[HMM_PFN_VALID]);
> @@ -259,25 +250,6 @@ static int hmm_vma_handle_pte(struct mm_walk *walk,
unsigned long addr,
>   	if (!pte_present(pte)) {
>   		swp_entry_t entry = pte_to_swp_entry(pte);
>   
> -		/*
> -		 * This is a special swap entry, ignore migration, use
> -		 * device and report anything else as error.
> -		 */
> -		if (is_device_private_entry(entry)) {
> -			cpu_flags = range->flags[HMM_PFN_VALID] |
> -				range->flags[HMM_PFN_DEVICE_PRIVATE];
> -			cpu_flags |= is_write_device_private_entry(entry) ?
> -				range->flags[HMM_PFN_WRITE] : 0;
> -			hmm_pte_need_fault(hmm_vma_walk, orig_pfn, cpu_flags,
> -					   &fault, &write_fault);
> -			if (fault || write_fault)
> -				goto fault;
> -			*pfn = hmm_device_entry_from_pfn(range,
> -					    swp_offset(entry));
> -			*pfn |= cpu_flags;
> -			return 0;
> -		}
> -
>   		hmm_pte_need_fault(hmm_vma_walk, orig_pfn, 0, &fault,
>   				   &write_fault);
>   		if (!fault && !write_fault)
>

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