patches/old/lib-test_hmm-add-large-page-allocation-failure-testing.patch

From: Balbir Singh <balbirs@nvidia.com>
Subject: lib/test_hmm: add large page allocation failure testing
Date: Mon, 8 Sep 2025 10:04:44 +1000

Add HMM_DMIRROR_FLAG_FAIL_ALLOC flag to simulate large page allocation
failures, enabling testing of split migration code paths.

This test flag allows validation of the fallback behavior when destination
device cannot allocate compound pages.  This is useful for testing the
split migration functionality.

Link: https://lkml.kernel.org/r/20250908000448.180088-12-balbirs@nvidia.com
Signed-off-by: Balbir Singh <balbirs@nvidia.com>
Cc: David Hildenbrand <david@redhat.com>
Cc: Zi Yan <ziy@nvidia.com>
Cc: Joshua Hahn <joshua.hahnjy@gmail.com>
Cc: Rakie Kim <rakie.kim@sk.com>
Cc: Byungchul Park <byungchul@sk.com>
Cc: Gregory Price <gourry@gourry.net>
Cc: Ying Huang <ying.huang@linux.alibaba.com>
Cc: Alistair Popple <apopple@nvidia.com>
Cc: Oscar Salvador <osalvador@suse.de>
Cc: Lorenzo Stoakes <lorenzo.stoakes@oracle.com>
Cc: Baolin Wang <baolin.wang@linux.alibaba.com>
Cc: "Liam R. Howlett" <Liam.Howlett@oracle.com>
Cc: Nico Pache <npache@redhat.com>
Cc: Ryan Roberts <ryan.roberts@arm.com>
Cc: Dev Jain <dev.jain@arm.com>
Cc: Barry Song <baohua@kernel.org>
Cc: Lyude Paul <lyude@redhat.com>
Cc: Danilo Krummrich <dakr@kernel.org>
Cc: David Airlie <airlied@gmail.com>
Cc: Simona Vetter <simona@ffwll.ch>
Cc: Ralph Campbell <rcampbell@nvidia.com>
Cc: Mika Penttilä <mpenttil@redhat.com>
Cc: Matthew Brost <matthew.brost@intel.com>
Cc: Francois Dugast <francois.dugast@intel.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
---

 lib/test_hmm.c      |   61 ++++++++++++++++++++++++++++--------------
 lib/test_hmm_uapi.h |    3 ++
 2 files changed, 44 insertions(+), 20 deletions(-)

--- a/lib/test_hmm.c~lib-test_hmm-add-large-page-allocation-failure-testing
+++ a/lib/test_hmm.c
@@ -92,6 +92,7 @@ struct dmirror {
 	struct xarray			pt;
 	struct mmu_interval_notifier	notifier;
 	struct mutex			mutex;
+	__u64			flags;
 };
 
 /*
@@ -699,7 +700,12 @@ static void dmirror_migrate_alloc_and_co
 		     page_to_pfn(spage)))
 			goto next;
 
-		dpage = dmirror_devmem_alloc_page(dmirror, is_large);
+		if (dmirror->flags & HMM_DMIRROR_FLAG_FAIL_ALLOC) {
+			dmirror->flags &= ~HMM_DMIRROR_FLAG_FAIL_ALLOC;
+			dpage = NULL;
+		} else
+			dpage = dmirror_devmem_alloc_page(dmirror, is_large);
+
 		if (!dpage) {
 			struct folio *folio;
 			unsigned long i;
@@ -959,44 +965,55 @@ static vm_fault_t dmirror_devmem_fault_a
 
 		spage = BACKING_PAGE(spage);
 		order = folio_order(page_folio(spage));
-
 		if (order)
+			*dst = MIGRATE_PFN_COMPOUND;
+		if (*src & MIGRATE_PFN_WRITE)
+			*dst |= MIGRATE_PFN_WRITE;
+
+		if (dmirror->flags & HMM_DMIRROR_FLAG_FAIL_ALLOC) {
+			dmirror->flags &= ~HMM_DMIRROR_FLAG_FAIL_ALLOC;
+			*dst &= ~MIGRATE_PFN_COMPOUND;
+			dpage = NULL;
+		} else if (order) {
 			dpage = folio_page(vma_alloc_folio(GFP_HIGHUSER_MOVABLE,
 						order, args->vma, addr), 0);
-		else
-			dpage = alloc_page_vma(GFP_HIGHUSER_MOVABLE, args->vma, addr);
-
-		/* Try with smaller pages if large allocation fails */
-		if (!dpage && order) {
+		} else {
 			dpage = alloc_page_vma(GFP_HIGHUSER_MOVABLE, args->vma, addr);
-			if (!dpage)
-				return VM_FAULT_OOM;
-			order = 0;
 		}
 
+		if (!dpage && !order)
+			return VM_FAULT_OOM;
+
 		pr_debug("migrating from sys to dev pfn src: 0x%lx pfn dst: 0x%lx\n",
 				page_to_pfn(spage), page_to_pfn(dpage));
-		lock_page(dpage);
-		xa_erase(&dmirror->pt, addr >> PAGE_SHIFT);
-		copy_highpage(dpage, spage);
-		*dst = migrate_pfn(page_to_pfn(dpage));
-		if (*src & MIGRATE_PFN_WRITE)
-			*dst |= MIGRATE_PFN_WRITE;
-		if (order)
-			*dst |= MIGRATE_PFN_COMPOUND;
+
+		if (dpage) {
+			lock_page(dpage);
+			*dst |= migrate_pfn(page_to_pfn(dpage));
+		}
 
 		for (i = 0; i < (1 << order); i++) {
 			struct page *src_page;
 			struct page *dst_page;
 
+			/* Try with smaller pages if large allocation fails */
+			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_page = pfn_to_page(page_to_pfn(dpage));
+				dpage = NULL; /* For the next iteration */
+			} else {
+				dst_page = pfn_to_page(page_to_pfn(dpage) + i);
+			}
+
 			src_page = pfn_to_page(page_to_pfn(spage) + i);
-			dst_page = pfn_to_page(page_to_pfn(dpage) + i);
 
 			xa_erase(&dmirror->pt, addr >> PAGE_SHIFT);
+			addr += PAGE_SIZE;
 			copy_highpage(dst_page, src_page);
 		}
 next:
-		addr += PAGE_SIZE << order;
 		src += 1 << order;
 		dst += 1 << order;
 	}
@@ -1514,6 +1531,10 @@ static long dmirror_fops_unlocked_ioctl(
 		dmirror_device_remove_chunks(dmirror->mdevice);
 		ret = 0;
 		break;
+	case HMM_DMIRROR_FLAGS:
+		dmirror->flags = cmd.npages;
+		ret = 0;
+		break;
 
 	default:
 		return -EINVAL;
--- a/lib/test_hmm_uapi.h~lib-test_hmm-add-large-page-allocation-failure-testing
+++ a/lib/test_hmm_uapi.h
@@ -37,6 +37,9 @@ struct hmm_dmirror_cmd {
 #define HMM_DMIRROR_EXCLUSIVE		_IOWR('H', 0x05, struct hmm_dmirror_cmd)
 #define HMM_DMIRROR_CHECK_EXCLUSIVE	_IOWR('H', 0x06, struct hmm_dmirror_cmd)
 #define HMM_DMIRROR_RELEASE		_IOWR('H', 0x07, struct hmm_dmirror_cmd)
+#define HMM_DMIRROR_FLAGS		_IOWR('H', 0x08, struct hmm_dmirror_cmd)
+
+#define HMM_DMIRROR_FLAG_FAIL_ALLOC	(1ULL << 0)
 
 /*
  * Values returned in hmm_dmirror_cmd.ptr for HMM_DMIRROR_SNAPSHOT.
_