mm: handle multiple owners of device private pages in migrate_vma

Add a new src_owner field to struct migrate_vma. If the field is set,
only device private pages with page->pgmap->owner equal to that field are
migrated. If the field is not set only "normal" pages are migrated.

Fixes: df6ad69838fc ("mm/device-public-memory: device memory cache coherent with CPU")
Link: https://lore.kernel.org/r/[e-mail]
Signed-off-by: Christoph Hellwig <[e-mail]>
Reviewed-by: Ralph Campbell <[e-mail]>
Tested-by: Bharata B Rao <[e-mail]>
Signed-off-by: Jason Gunthorpe <[e-mail]>

arch/powerpc/kvm/book3s_hv_uvmem.c

···
 	mig.end = end;
 	mig.src = &src_pfn;
 	mig.dst = &dst_pfn;
+	mig.src_owner = &kvmppc_uvmem_pgmap;
 
 	mutex_lock(&kvm->arch.uvmem_lock);
 	/* The requested page is already paged-out, nothing to do */

drivers/gpu/drm/nouveau/nouveau_dmem.c

···
 		.end		= vmf->address + PAGE_SIZE,
 		.src		= &src,
 		.dst		= &dst,
+		.src_owner	= drm->dev,
 	};
 
 	/*

include/linux/migrate.h

···
 	unsigned long		npages;
 	unsigned long		start;
 	unsigned long		end;
+
+	/*
+	 * 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.
+	 */
+	void			*src_owner;
 };
 
 int migrate_vma_setup(struct migrate_vma *args);

mm/migrate.c

···
 	arch_enter_lazy_mmu_mode();
 
 	for (; addr < end; addr += PAGE_SIZE, ptep++) {
-		unsigned long mpfn, pfn;
+		unsigned long mpfn = 0, pfn;
 		struct page *page;
 		swp_entry_t entry;
 		pte_t pte;
···
 		}
 
 		if (!pte_present(pte)) {
-			mpfn = 0;
-
 			/*
 			 * Only care about unaddressable device page special
 			 * page table entry. Other special swap entries are not
···
 				goto next;
 
 			page = device_private_entry_to_page(entry);
+			if (page->pgmap->owner != migrate->src_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)
+				goto next;
 			pfn = pte_pfn(pte);
 			if (is_zero_pfn(pfn)) {
 				mpfn = MIGRATE_PFN_MIGRATE;