mm/rmap: convert make_device_exclusive_range() to make_device_exclusive()

The single "real" user in the tree of make_device_exclusive_range() always
requests making only a single address exclusive.  The current
implementation is hard to fix for properly supporting anonymous THP /
large folios and for avoiding messing with rmap walks in weird ways.

So let's always process a single address/page and return folio + page to
minimize page -> folio lookups.  This is a preparation for further
changes.

Reject any non-anonymous or hugetlb folios early, directly after GUP.

While at it, extend the documentation of make_device_exclusive() to
clarify some things.

Link: https://lkml.kernel.org/r/20250210193801.781278-4-david@redhat.com
Signed-off-by: David Hildenbrand <david@redhat.com>
Acked-by: Simona Vetter <simona.vetter@ffwll.ch>
Reviewed-by: Alistair Popple <apopple@nvidia.com>
Tested-by: Alistair Popple <apopple@nvidia.com>
Cc: Alex Shi <alexs@kernel.org>
Cc: Danilo Krummrich <dakr@kernel.org>
Cc: Dave Airlie <airlied@gmail.com>
Cc: Jann Horn <jannh@google.com>
Cc: Jason Gunthorpe <jgg@nvidia.com>
Cc: Jerome Glisse <jglisse@redhat.com>
Cc: John Hubbard <jhubbard@nvidia.com>
Cc: Jonathan Corbet <corbet@lwn.net>
Cc: Karol Herbst <kherbst@redhat.com>
Cc: Liam Howlett <liam.howlett@oracle.com>
Cc: Lorenzo Stoakes <lorenzo.stoakes@oracle.com>
Cc: Lyude <lyude@redhat.com>
Cc: "Masami Hiramatsu (Google)" <mhiramat@kernel.org>
Cc: Oleg Nesterov <oleg@redhat.com>
Cc: Pasha Tatashin <pasha.tatashin@soleen.com>
Cc: Peter Xu <peterx@redhat.com>
Cc: Peter Zijlstra (Intel) <peterz@infradead.org>
Cc: SeongJae Park <sj@kernel.org>
Cc: Vlastimil Babka <vbabka@suse.cz>
Cc: Yanteng Si <si.yanteng@linux.dev>
Cc: Barry Song <v-songbaohua@oppo.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

1 files changed, 15 insertions, 26 deletions

diff --git a/lib/test_hmm.c b/lib/test_hmm.c
index 056f2e411d7b..e4afca8d1880 100644
--- a/lib/test_hmm.c
+++ b/lib/test_hmm.c
@@ -780,10 +780,8 @@ static int dmirror_exclusive(struct dmirror *dmirror,
 	unsigned long start, end, addr;
 	unsigned long size = cmd->npages << PAGE_SHIFT;
 	struct mm_struct *mm = dmirror->notifier.mm;
-	struct page *pages[64];
 	struct dmirror_bounce bounce;
-	unsigned long next;
-	int ret;
+	int ret = 0;
 
 	start = cmd->addr;
 	end = start + size;
@@ -795,36 +793,27 @@ static int dmirror_exclusive(struct dmirror *dmirror,
 		return -EINVAL;
 
 	mmap_read_lock(mm);
-	for (addr = start; addr < end; addr = next) {
-		unsigned long mapped = 0;
-		int i;
-
-		next = min(end, addr + (ARRAY_SIZE(pages) << PAGE_SHIFT));
+	for (addr = start; !ret && addr < end; addr += PAGE_SIZE) {
+		struct folio *folio;
+		struct page *page;
 
-		ret = make_device_exclusive_range(mm, addr, next, pages, NULL);
-		/*
-		 * Do dmirror_atomic_map() iff all pages are marked for
-		 * exclusive access to avoid accessing uninitialized
-		 * fields of pages.
-		 */
-		if (ret == (next - addr) >> PAGE_SHIFT)
-			mapped = dmirror_atomic_map(addr, next, pages, dmirror);
-		for (i = 0; i < ret; i++) {
-			if (pages[i]) {
-				unlock_page(pages[i]);
-				put_page(pages[i]);
-			}
+		page = make_device_exclusive(mm, addr, NULL, &folio);
+		if (IS_ERR(page)) {
+			ret = PTR_ERR(page);
+			break;
 		}
 
-		if (addr + (mapped << PAGE_SHIFT) < next) {
-			mmap_read_unlock(mm);
-			mmput(mm);
-			return -EBUSY;
-		}
+		ret = dmirror_atomic_map(addr, addr + PAGE_SIZE, &page, dmirror);
+		ret = ret == 1 ? 0 : -EBUSY;
+		folio_unlock(folio);
+		folio_put(folio);
 	}
 	mmap_read_unlock(mm);
 	mmput(mm);
 
+	if (ret)
+		return ret;
+
 	/* Return the migrated data for verification. */
 	ret = dmirror_bounce_init(&bounce, start, size);
 	if (ret)