mm/migrate: add a flags parameter to migrate_vma

The src_owner field in struct migrate_vma is being used for two purposes,
it acts as a selection filter for which types of pages are to be migrated
and it identifies device private pages owned by the caller.

Split this into separate parameters so the src_owner field can be used
just to identify device private pages owned by the caller of
migrate_vma_setup().

Rename the src_owner field to pgmap_owner to reflect it is now used only
to identify which device private pages to migrate.

Link: https://lore.kernel.org/r/20200723223004.9586-3-rcampbell@nvidia.com
Signed-off-by: Ralph Campbell <rcampbell@nvidia.com>
Reviewed-by: Bharata B Rao <bharata@linux.ibm.com>
Signed-off-by: Jason Gunthorpe <jgg@nvidia.com>

arch/powerpc/kvm/book3s_hv_uvmem.c

@@ -400,6 +400,7 @@ kvmppc_svm_page_in(struct vm_area_struct *vma, unsigned long start,
 	mig.end = end;
 	mig.src = &src_pfn;
 	mig.dst = &dst_pfn;
+	mig.flags = MIGRATE_VMA_SELECT_SYSTEM;
 
 	/*
 	 * We come here with mmap_lock write lock held just for
@@ -577,7 +578,8 @@ kvmppc_svm_page_out(struct vm_area_struct *vma, unsigned long start,
 	mig.end = end;
 	mig.src = &src_pfn;
 	mig.dst = &dst_pfn;
-	mig.src_owner = &kvmppc_uvmem_pgmap;
+	mig.pgmap_owner = &kvmppc_uvmem_pgmap;
+	mig.flags = MIGRATE_VMA_SELECT_DEVICE_PRIVATE;
 
 	mutex_lock(&kvm->arch.uvmem_lock);
 	/* The requested page is already paged-out, nothing to do */

drivers/gpu/drm/nouveau/nouveau_dmem.c

@@ -182,7 +182,8 @@ static vm_fault_t nouveau_dmem_migrate_to_ram(struct vm_fault *vmf)
 		.end		= vmf->address + PAGE_SIZE,
 		.src		= &src,
 		.dst		= &dst,
-		.src_owner	= drm->dev,
+		.pgmap_owner	= drm->dev,
+		.flags		= MIGRATE_VMA_SELECT_DEVICE_PRIVATE,
 	};
 
 	/*
@@ -615,6 +616,7 @@ nouveau_dmem_migrate_vma(struct nouveau_drm *drm,
 	struct migrate_vma args = {
 		.vma		= vma,
 		.start		= start,
+		.flags		= MIGRATE_VMA_SELECT_SYSTEM,
 	};
 	unsigned long i;
 	u64 *pfns;

include/linux/migrate.h

@@ -180,6 +180,11 @@ static inline unsigned long migrate_pfn(unsigned long pfn)
 	return (pfn << MIGRATE_PFN_SHIFT) | MIGRATE_PFN_VALID;
 }
 
+enum migrate_vma_direction {
+	MIGRATE_VMA_SELECT_SYSTEM = 1 << 0,
+	MIGRATE_VMA_SELECT_DEVICE_PRIVATE = 1 << 1,
+};
+
 struct migrate_vma {
 	struct vm_area_struct	*vma;
 	/*
@@ -199,11 +204,11 @@ struct migrate_vma {
 
 	/*
 	 * Set to the owner value also stored in page->pgmap->owner for
-	 * migrating out of device private memory.  If set only device
-	 * private pages with this owner are migrated.  If not set
-	 * device private pages are not migrated at all.
+	 * migrating out of device private memory. The flags also need to
+	 * be set to MIGRATE_VMA_SELECT_DEVICE_PRIVATE.
 	 */
-	void			*src_owner;
+	void			*pgmap_owner;
+	unsigned long		flags;
 };
 
 int migrate_vma_setup(struct migrate_vma *args);

lib/test_hmm.c

@@ -585,15 +585,6 @@ static void dmirror_migrate_alloc_and_copy(struct migrate_vma *args,
 		 */
 		spage = migrate_pfn_to_page(*src);
 
-		/*
-		 * Don't migrate device private pages from our own driver or
-		 * others. For our own we would do a device private memory copy
-		 * not a migration and for others, we would need to fault the
-		 * other device's page into system memory first.
-		 */
-		if (spage && is_zone_device_page(spage))
-			continue;
-
 		dpage = dmirror_devmem_alloc_page(mdevice);
 		if (!dpage)
 			continue;
@@ -702,7 +693,8 @@ static int dmirror_migrate(struct dmirror *dmirror,
 		args.dst = dst_pfns;
 		args.start = addr;
 		args.end = next;
-		args.src_owner = NULL;
+		args.pgmap_owner = NULL;
+		args.flags = MIGRATE_VMA_SELECT_SYSTEM;
 		ret = migrate_vma_setup(&args);
 		if (ret)
 			goto out;
@@ -1053,7 +1045,8 @@ static vm_fault_t dmirror_devmem_fault(struct vm_fault *vmf)
 	args.end = args.start + PAGE_SIZE;
 	args.src = &src_pfns;
 	args.dst = &dst_pfns;
-	args.src_owner = dmirror->mdevice;
+	args.pgmap_owner = dmirror->mdevice;
+	args.flags = MIGRATE_VMA_SELECT_DEVICE_PRIVATE;
 
 	if (migrate_vma_setup(&args))
 		return VM_FAULT_SIGBUS;

mm/migrate.c

@@ -2287,15 +2287,17 @@ static int migrate_vma_collect_pmd(pmd_t *pmdp,
 				goto next;
 
 			page = device_private_entry_to_page(entry);
-			if (page->pgmap->owner != migrate->src_owner)
+			if (!(migrate->flags &
+				MIGRATE_VMA_SELECT_DEVICE_PRIVATE) ||
+			    page->pgmap->owner != migrate->pgmap_owner)
 				goto next;
 
 			mpfn = migrate_pfn(page_to_pfn(page)) |
 					MIGRATE_PFN_MIGRATE;
 			if (is_write_device_private_entry(entry))
 				mpfn |= MIGRATE_PFN_WRITE;
 		} else {
-			if (migrate->src_owner)
+			if (!(migrate->flags & MIGRATE_VMA_SELECT_SYSTEM))
 				goto next;
 			pfn = pte_pfn(pte);
 			if (is_zero_pfn(pfn)) {