block/bdev: lift block size restrictions to 64k

We now can support blocksizes larger than PAGE_SIZE, so in theory
we should be able to lift the restriction up to the max supported page
cache order. However bound ourselves to what we can currently validate
and test. Through blktests and fstest we can validate up to 64k today.

Reviewed-by: Hannes Reinecke <hare@suse.de>
Reviewed-by: "Matthew Wilcox (Oracle)" <willy@infradead.org>
Signed-off-by: Luis Chamberlain <mcgrof@kernel.org>
Link: https://lore.kernel.org/r/20250221223823.1680616-8-mcgrof@kernel.org
Signed-off-by: Christian Brauner <brauner@kernel.org>

Author: mcgrof

block/bdev.c

@@ -183,8 +183,7 @@ int sb_set_blocksize(struct super_block *sb, int size)
 {
 	if (set_blocksize(sb->s_bdev_file, size))
 		return 0;
-	/* If we get here, we know size is power of two
-	 * and it's value is between 512 and PAGE_SIZE */
+	/* If we get here, we know size is validated */
 	sb->s_blocksize = size;
 	sb->s_blocksize_bits = blksize_bits(size);
 	return sb->s_blocksize;

include/linux/blkdev.h

@@ -267,10 +267,16 @@ static inline dev_t disk_devt(struct gendisk *disk)
 	return MKDEV(disk->major, disk->first_minor);
 }
 
+/*
+ * We should strive for 1 << (PAGE_SHIFT + MAX_PAGECACHE_ORDER)
+ * however we constrain this to what we can validate and test.
+ */
+#define BLK_MAX_BLOCK_SIZE      SZ_64K
+
 /* blk_validate_limits() validates bsize, so drivers don't usually need to */
 static inline int blk_validate_block_size(unsigned long bsize)
 {
-	if (bsize < 512 || bsize > PAGE_SIZE || !is_power_of_2(bsize))
+	if (bsize < 512 || bsize > BLK_MAX_BLOCK_SIZE || !is_power_of_2(bsize))
 		return -EINVAL;
 
 	return 0;