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

[Christoph Hellwig <hch@lst.de>]

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@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