get rid of separate multipage fault-in primitives

* the only remaining callers of "short" fault-ins are just as happy with generic
variants (both in lib/iov_iter.c); switch them to multipage variants, kill the
"short" ones
* rename the multipage variants to now available plain ones.
* get rid of compat macro defining iov_iter_fault_in_multipage_readable by
expanding it in its only user.
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>

drivers/gpu/drm/armada/armada_gem.c

@@ -387,7 +387,7 @@ int armada_gem_pwrite_ioctl(struct drm_device *dev, void *data,
 	if (!access_ok(VERIFY_READ, ptr, args->size))
 		return -EFAULT;
 
-	ret = fault_in_multipages_readable(ptr, args->size);
+	ret = fault_in_pages_readable(ptr, args->size);
 	if (ret)
 		return ret;
 

drivers/gpu/drm/i915/i915_gem.c

@@ -675,7 +675,7 @@ i915_gem_gtt_pread(struct drm_device *dev,
 
 	mutex_unlock(&dev->struct_mutex);
 	if (likely(!i915.prefault_disable)) {
-		ret = fault_in_multipages_writeable(user_data, remain);
+		ret = fault_in_pages_writeable(user_data, remain);
 		if (ret) {
 			mutex_lock(&dev->struct_mutex);
 			goto out_unpin;
@@ -803,7 +803,7 @@ i915_gem_shmem_pread(struct drm_device *dev,
 		mutex_unlock(&dev->struct_mutex);
 
 		if (likely(!i915.prefault_disable) && !prefaulted) {
-			ret = fault_in_multipages_writeable(user_data, remain);
+			ret = fault_in_pages_writeable(user_data, remain);
 			/* Userspace is tricking us, but we've already clobbered
 			 * its pages with the prefault and promised to write the
 			 * data up to the first fault. Hence ignore any errors
@@ -1267,7 +1267,7 @@ i915_gem_pwrite_ioctl(struct drm_device *dev, void *data,
 		return -EFAULT;
 
 	if (likely(!i915.prefault_disable)) {
-		ret = fault_in_multipages_readable(u64_to_user_ptr(args->data_ptr),
+		ret = fault_in_pages_readable(u64_to_user_ptr(args->data_ptr),
 						   args->size);
 		if (ret)
 			return -EFAULT;

drivers/gpu/drm/i915/i915_gem_execbuffer.c

@@ -1048,7 +1048,7 @@ validate_exec_list(struct drm_device *dev,
 			return -EFAULT;
 
 		if (likely(!i915.prefault_disable)) {
-			if (fault_in_multipages_readable(ptr, length))
+			if (fault_in_pages_readable(ptr, length))
 				return -EFAULT;
 		}
 	}

fs/ntfs/file.c

@@ -1850,7 +1850,7 @@ static ssize_t ntfs_perform_write(struct file *file, struct iov_iter *i,
 		 * pages being swapped out between us bringing them into memory
 		 * and doing the actual copying.
 		 */
-		if (unlikely(iov_iter_fault_in_multipages_readable(i, bytes))) {
+		if (unlikely(iov_iter_fault_in_readable(i, bytes))) {
 			status = -EFAULT;
 			break;
 		}

include/linux/pagemap.h

@@ -518,58 +518,9 @@ void page_endio(struct page *page, bool is_write, int err);
 extern void add_page_wait_queue(struct page *page, wait_queue_t *waiter);
 
 /*
- * Fault one or two userspace pages into pagetables.
- * Return -EINVAL if more than two pages would be needed.
- * Return non-zero on a fault.
+ * Fault everything in given userspace address range in.
  */
 static inline int fault_in_pages_writeable(char __user *uaddr, int size)
-{
-	int span, ret;
-
-	if (unlikely(size == 0))
-		return 0;
-
-	span = offset_in_page(uaddr) + size;
-	if (span > 2 * PAGE_SIZE)
-		return -EINVAL;
-	/*
-	 * Writing zeroes into userspace here is OK, because we know that if
-	 * the zero gets there, we'll be overwriting it.
-	 */
-	ret = __put_user(0, uaddr);
-	if (ret == 0 && span > PAGE_SIZE)
-		ret = __put_user(0, uaddr + size - 1);
-	return ret;
-}
-
-static inline int fault_in_pages_readable(const char __user *uaddr, int size)
-{
-	volatile char c;
-	int ret;
-
-	if (unlikely(size == 0))
-		return 0;
-
-	ret = __get_user(c, uaddr);
-	if (ret == 0) {
-		const char __user *end = uaddr + size - 1;
-
-		if (((unsigned long)uaddr & PAGE_MASK) !=
-				((unsigned long)end & PAGE_MASK)) {
-			ret = __get_user(c, end);
-			(void)c;
-		}
-	}
-	return ret;
-}
-
-/*
- * Multipage variants of the above prefault helpers, useful if more than
- * PAGE_SIZE of data needs to be prefaulted. These are separate from the above
- * functions (which only handle up to PAGE_SIZE) to avoid clobbering the
- * filemap.c hotpaths.
- */
-static inline int fault_in_multipages_writeable(char __user *uaddr, int size)
 {
 	char __user *end = uaddr + size - 1;
 
@@ -596,8 +547,7 @@ static inline int fault_in_multipages_writeable(char __user *uaddr, int size)
 	return 0;
 }
 
-static inline int fault_in_multipages_readable(const char __user *uaddr,
-					       int size)
+static inline int fault_in_pages_readable(const char __user *uaddr, int size)
 {
 	volatile char c;
 	const char __user *end = uaddr + size - 1;

include/linux/uio.h

@@ -76,7 +76,6 @@ size_t iov_iter_copy_from_user_atomic(struct page *page,
 		struct iov_iter *i, unsigned long offset, size_t bytes);
 void iov_iter_advance(struct iov_iter *i, size_t bytes);
 int iov_iter_fault_in_readable(struct iov_iter *i, size_t bytes);
-#define iov_iter_fault_in_multipages_readable iov_iter_fault_in_readable
 size_t iov_iter_single_seg_count(const struct iov_iter *i);
 size_t copy_page_to_iter(struct page *page, size_t offset, size_t bytes,
 			 struct iov_iter *i);

lib/iov_iter.c

@@ -306,8 +306,7 @@ int iov_iter_fault_in_readable(struct iov_iter *i, size_t bytes)
 
 	if (!(i->type & (ITER_BVEC|ITER_KVEC))) {
 		iterate_iovec(i, bytes, v, iov, skip, ({
-			err = fault_in_multipages_readable(v.iov_base,
-					v.iov_len);
+			err = fault_in_pages_readable(v.iov_base, v.iov_len);
 			if (unlikely(err))
 			return err;
 		0;}))