block: make segment size limit workable for > 4K PAGE_SIZE

JIRA: https://issues.redhat.com/browse/RHEL-79409

commit 889c570
Author: Ming Lei <ming.lei@redhat.com>
Date:   Tue Feb 25 10:21:41 2025 +0800

    block: make segment size limit workable for > 4K PAGE_SIZE

    Using PAGE_SIZE as a minimum expected DMA segment size in consideration
    of devices which have a max DMA segment size of < 64k when used on 64k
    PAGE_SIZE systems leads to devices not being able to probe such as
    eMMC and Exynos UFS controller [0] [1] you can end up with a probe failure
    as follows:

    WARNING: CPU: 2 PID: 397 at block/blk-settings.c:339 blk_validate_limits+0x364/0x3c0

    Ensure we use min(max_seg_size, seg_boundary_mask + 1) as the new min segment
    size when max segment size is < PAGE_SIZE for 16k and 64k base page size systems.

    If anyone need to backport this patch, the following commits are depended:

            commit 6aeb4f8 ("block: remove bio_add_pc_page")
            commit 02ee5d6 ("block: remove blk_rq_bio_prep")
            commit b7175e2 ("block: add a dma mapping iterator")

    Link: https://lore.kernel.org/linux-block/20230612203314.17820-1-bvanassche@acm.org/ # [0]
    Link: https://lore.kernel.org/linux-block/1d55e942-5150-de4c-3a02-c3d066f87028@acm.org/ # [1]
    Cc: Yi Zhang <yi.zhang@redhat.com>
    Cc: John Garry <john.g.garry@oracle.com>
    Cc: Keith Busch <kbusch@kernel.org>
    Tested-by: Paul Bunyan <pbunyan@redhat.com>
    Reviewed-by: Daniel Gomez <da.gomez@kernel.org>
    Reviewed-by: Luis Chamberlain <mcgrof@kernel.org>
    Reviewed-by: Bart Van Assche <bvanassche@acm.org>
    Signed-off-by: Ming Lei <ming.lei@redhat.com>
    Link: https://lore.kernel.org/r/20250225022141.2154581-1-ming.lei@redhat.com
    Signed-off-by: Jens Axboe <axboe@kernel.dk>

Signed-off-by: Ming Lei <ming.lei@redhat.com>

Author: Ming Lei

block/blk-merge.c

@@ -329,7 +329,7 @@ int bio_split_rw_at(struct bio *bio, const struct queue_limits *lim,
 
 		if (nsegs < lim->max_segments &&
 		    bytes + bv.bv_len <= max_bytes &&
-		    bv.bv_offset + bv.bv_len <= PAGE_SIZE) {
+		    bv.bv_offset + bv.bv_len <= lim->min_segment_size) {
 			nsegs++;
 			bytes += bv.bv_len;
 		} else {

block/blk-settings.c

@@ -246,6 +246,7 @@ int blk_validate_limits(struct queue_limits *lim)
 {
 	unsigned int max_hw_sectors;
 	unsigned int logical_block_sectors;
+	unsigned long seg_size;
 	int err;
 
 	/*
@@ -303,7 +304,7 @@ int blk_validate_limits(struct queue_limits *lim)
 	max_hw_sectors = min_not_zero(lim->max_hw_sectors,
 				lim->max_dev_sectors);
 	if (lim->max_user_sectors) {
-		if (lim->max_user_sectors < PAGE_SIZE / SECTOR_SIZE)
+		if (lim->max_user_sectors < BLK_MIN_SEGMENT_SIZE / SECTOR_SIZE)
 			return -EINVAL;
 		lim->max_sectors = min(max_hw_sectors, lim->max_user_sectors);
 	} else if (lim->io_opt > (BLK_DEF_MAX_SECTORS_CAP << SECTOR_SHIFT)) {
@@ -341,7 +342,7 @@ int blk_validate_limits(struct queue_limits *lim)
 	 */
 	if (!lim->seg_boundary_mask)
 		lim->seg_boundary_mask = BLK_SEG_BOUNDARY_MASK;
-	if (WARN_ON_ONCE(lim->seg_boundary_mask < PAGE_SIZE - 1))
+	if (WARN_ON_ONCE(lim->seg_boundary_mask < BLK_MIN_SEGMENT_SIZE - 1))
 		return -EINVAL;
 
 	/*
@@ -362,10 +363,17 @@ int blk_validate_limits(struct queue_limits *lim)
 		 */
 		if (!lim->max_segment_size)
 			lim->max_segment_size = BLK_MAX_SEGMENT_SIZE;
-		if (WARN_ON_ONCE(lim->max_segment_size < PAGE_SIZE))
+		if (WARN_ON_ONCE(lim->max_segment_size < BLK_MIN_SEGMENT_SIZE))
 			return -EINVAL;
 	}
 
+	/* setup min segment size for building new segment in fast path */
+	if (lim->seg_boundary_mask > lim->max_segment_size - 1)
+		seg_size = lim->max_segment_size;
+	else
+		seg_size = lim->seg_boundary_mask + 1;
+	lim->min_segment_size = min_t(unsigned int, seg_size, PAGE_SIZE);
+
 	/*
 	 * We require drivers to at least do logical block aligned I/O, but
 	 * historically could not check for that due to the separate calls

block/blk.h

@@ -14,6 +14,7 @@
 struct elevator_type;
 
 #define	BLK_DEV_MAX_SECTORS	(LLONG_MAX >> 9)
+#define	BLK_MIN_SEGMENT_SIZE	4096
 
 /* Max future timer expiry for timeouts */
 #define BLK_MAX_TIMEOUT		(5 * HZ)
@@ -358,8 +359,12 @@ struct bio *bio_split_zone_append(struct bio *bio,
 static inline bool bio_may_need_split(struct bio *bio,
 		const struct queue_limits *lim)
 {
-	return lim->chunk_sectors || bio->bi_vcnt != 1 ||
-		bio->bi_io_vec->bv_len + bio->bi_io_vec->bv_offset > PAGE_SIZE;
+	if (lim->chunk_sectors)
+		return true;
+	if (bio->bi_vcnt != 1)
+		return true;
+	return bio->bi_io_vec->bv_len + bio->bi_io_vec->bv_offset >
+		lim->min_segment_size;
 }
 
 /**

include/linux/blkdev.h

@@ -375,6 +375,7 @@ struct queue_limits {
 	unsigned int		max_sectors;
 	unsigned int		max_user_sectors;
 	unsigned int		max_segment_size;
+	unsigned int		min_segment_size;
 	unsigned int		physical_block_size;
 	unsigned int		logical_block_size;
 	unsigned int		alignment_offset;