fs/aio: Stop allocating aio rings from HIGHMEM

There is no need to allocate aio rings from HIGHMEM because of very
little memory needed here.

Therefore, use GFP_USER flag in find_or_create_page() and get rid of
kmap*() mappings.

Cc: Al Viro <viro@zeniv.linux.org.uk>
Cc: Ira Weiny <ira.weiny@intel.com>
Suggested-by: Matthew Wilcox <willy@infradead.org>
Signed-off-by: Fabio M. De Francesco <fmdefrancesco@gmail.com>
Reviewed-by: Ira Weiny <ira.weiny@intel.com>
Message-Id: <20230609145937.17610-1-fmdefrancesco@gmail.com>
Signed-off-by: Christian Brauner <brauner@kernel.org>

fs/aio.c

@@ -530,7 +530,7 @@ static int aio_setup_ring(struct kioctx *ctx, unsigned int nr_events)
 	for (i = 0; i < nr_pages; i++) {
 		struct page *page;
 		page = find_or_create_page(file->f_mapping,
-					   i, GFP_HIGHUSER | __GFP_ZERO);
+					   i, GFP_USER | __GFP_ZERO);
 		if (!page)
 			break;
 		pr_debug("pid(%d) page[%d]->count=%d\n",
@@ -571,7 +571,7 @@ static int aio_setup_ring(struct kioctx *ctx, unsigned int nr_events)
 	ctx->user_id = ctx->mmap_base;
 	ctx->nr_events = nr_events; /* trusted copy */
 
-	ring = kmap_atomic(ctx->ring_pages[0]);
+	ring = page_address(ctx->ring_pages[0]);
 	ring->nr = nr_events;	/* user copy */
 	ring->id = ~0U;
 	ring->head = ring->tail = 0;
@@ -579,7 +579,6 @@ static int aio_setup_ring(struct kioctx *ctx, unsigned int nr_events)
 	ring->compat_features = AIO_RING_COMPAT_FEATURES;
 	ring->incompat_features = AIO_RING_INCOMPAT_FEATURES;
 	ring->header_length = sizeof(struct aio_ring);
-	kunmap_atomic(ring);
 	flush_dcache_page(ctx->ring_pages[0]);
 
 	return 0;
@@ -682,9 +681,8 @@ static int ioctx_add_table(struct kioctx *ctx, struct mm_struct *mm)
 					 * we are protected from page migration
 					 * changes ring_pages by ->ring_lock.
 					 */
-					ring = kmap_atomic(ctx->ring_pages[0]);
+					ring = page_address(ctx->ring_pages[0]);
 					ring->id = ctx->id;
-					kunmap_atomic(ring);
 					return 0;
 				}
 
@@ -1025,9 +1023,8 @@ static void user_refill_reqs_available(struct kioctx *ctx)
 		 * against ctx->completed_events below will make sure we do the
 		 * safe/right thing.
 		 */
-		ring = kmap_atomic(ctx->ring_pages[0]);
+		ring = page_address(ctx->ring_pages[0]);
 		head = ring->head;
-		kunmap_atomic(ring);
 
 		refill_reqs_available(ctx, head, ctx->tail);
 	}
@@ -1133,12 +1130,11 @@ static void aio_complete(struct aio_kiocb *iocb)
 	if (++tail >= ctx->nr_events)
 		tail = 0;
 
-	ev_page = kmap_atomic(ctx->ring_pages[pos / AIO_EVENTS_PER_PAGE]);
+	ev_page = page_address(ctx->ring_pages[pos / AIO_EVENTS_PER_PAGE]);
 	event = ev_page + pos % AIO_EVENTS_PER_PAGE;
 
 	*event = iocb->ki_res;
 
-	kunmap_atomic(ev_page);
 	flush_dcache_page(ctx->ring_pages[pos / AIO_EVENTS_PER_PAGE]);
 
 	pr_debug("%p[%u]: %p: %p %Lx %Lx %Lx\n", ctx, tail, iocb,
@@ -1152,10 +1148,9 @@ static void aio_complete(struct aio_kiocb *iocb)
 
 	ctx->tail = tail;
 
-	ring = kmap_atomic(ctx->ring_pages[0]);
+	ring = page_address(ctx->ring_pages[0]);
 	head = ring->head;
 	ring->tail = tail;
-	kunmap_atomic(ring);
 	flush_dcache_page(ctx->ring_pages[0]);
 
 	ctx->completed_events++;
@@ -1215,10 +1210,9 @@ static long aio_read_events_ring(struct kioctx *ctx,
 	mutex_lock(&ctx->ring_lock);
 
 	/* Access to ->ring_pages here is protected by ctx->ring_lock. */
-	ring = kmap_atomic(ctx->ring_pages[0]);
+	ring = page_address(ctx->ring_pages[0]);
 	head = ring->head;
 	tail = ring->tail;
-	kunmap_atomic(ring);
 
 	/*
 	 * Ensure that once we've read the current tail pointer, that
@@ -1250,10 +1244,9 @@ static long aio_read_events_ring(struct kioctx *ctx,
 		avail = min(avail, nr - ret);
 		avail = min_t(long, avail, AIO_EVENTS_PER_PAGE - pos);
 
-		ev = kmap(page);
+		ev = page_address(page);
 		copy_ret = copy_to_user(event + ret, ev + pos,
 					sizeof(*ev) * avail);
-		kunmap(page);
 
 		if (unlikely(copy_ret)) {
 			ret = -EFAULT;
@@ -1265,9 +1258,8 @@ static long aio_read_events_ring(struct kioctx *ctx,
 		head %= ctx->nr_events;
 	}
 
-	ring = kmap_atomic(ctx->ring_pages[0]);
+	ring = page_address(ctx->ring_pages[0]);
 	ring->head = head;
-	kunmap_atomic(ring);
 	flush_dcache_page(ctx->ring_pages[0]);
 
 	pr_debug("%li  h%u t%u\n", ret, head, tail);