1 files changed, 88 insertions, 0 deletions

diff --git a/block/blk-settings.c b/block/blk-settings.c
index b19306804056..37fe4c8f6b6b 100644
--- a/block/blk-settings.c
+++ b/block/blk-settings.c
@@ -136,6 +136,92 @@ static int blk_validate_integrity_limits(struct queue_limits *lim)
 }
 
 /*
+ * Returns max guaranteed bytes which we can fit in a bio.
+ *
+ * We request that an atomic_write is ITER_UBUF iov_iter (so a single vector),
+ * so we assume that we can fit in at least PAGE_SIZE in a segment, apart from
+ * the first and last segments.
+ */
+static
+unsigned int blk_queue_max_guaranteed_bio(struct queue_limits *lim)
+{
+	unsigned int max_segments = min(BIO_MAX_VECS, lim->max_segments);
+	unsigned int length;
+
+	length = min(max_segments, 2) * lim->logical_block_size;
+	if (max_segments > 2)
+		length += (max_segments - 2) * PAGE_SIZE;
+
+	return length;
+}
+
+static void blk_atomic_writes_update_limits(struct queue_limits *lim)
+{
+	unsigned int unit_limit = min(lim->max_hw_sectors << SECTOR_SHIFT,
+					blk_queue_max_guaranteed_bio(lim));
+
+	unit_limit = rounddown_pow_of_two(unit_limit);
+
+	lim->atomic_write_max_sectors =
+		min(lim->atomic_write_hw_max >> SECTOR_SHIFT,
+			lim->max_hw_sectors);
+	lim->atomic_write_unit_min =
+		min(lim->atomic_write_hw_unit_min, unit_limit);
+	lim->atomic_write_unit_max =
+		min(lim->atomic_write_hw_unit_max, unit_limit);
+	lim->atomic_write_boundary_sectors =
+		lim->atomic_write_hw_boundary >> SECTOR_SHIFT;
+}
+
+static void blk_validate_atomic_write_limits(struct queue_limits *lim)
+{
+	unsigned int chunk_sectors = lim->chunk_sectors;
+	unsigned int boundary_sectors;
+
+	if (!lim->atomic_write_hw_max)
+		goto unsupported;
+
+	boundary_sectors = lim->atomic_write_hw_boundary >> SECTOR_SHIFT;
+
+	if (boundary_sectors) {
+		/*
+		 * A feature of boundary support is that it disallows bios to
+		 * be merged which would result in a merged request which
+		 * crosses either a chunk sector or atomic write HW boundary,
+		 * even though chunk sectors may be just set for performance.
+		 * For simplicity, disallow atomic writes for a chunk sector
+		 * which is non-zero and smaller than atomic write HW boundary.
+		 * Furthermore, chunk sectors must be a multiple of atomic
+		 * write HW boundary. Otherwise boundary support becomes
+		 * complicated.
+		 * Devices which do not conform to these rules can be dealt
+		 * with if and when they show up.
+		 */
+		if (WARN_ON_ONCE(do_div(chunk_sectors, boundary_sectors)))
+			goto unsupported;
+
+		/*
+		 * The boundary size just needs to be a multiple of unit_max
+		 * (and not necessarily a power-of-2), so this following check
+		 * could be relaxed in future.
+		 * Furthermore, if needed, unit_max could even be reduced so
+		 * that it is compliant with a !power-of-2 boundary.
+		 */
+		if (!is_power_of_2(boundary_sectors))
+			goto unsupported;
+	}
+
+	blk_atomic_writes_update_limits(lim);
+	return;
+
+unsupported:
+	lim->atomic_write_max_sectors = 0;
+	lim->atomic_write_boundary_sectors = 0;
+	lim->atomic_write_unit_min = 0;
+	lim->atomic_write_unit_max = 0;
+}
+
+/*
  * Check that the limits in lim are valid, initialize defaults for unset
  * values, and cap values based on others where needed.
  */
@@ -272,6 +358,8 @@ static int blk_validate_limits(struct queue_limits *lim)
 	if (!(lim->features & BLK_FEAT_WRITE_CACHE))
 		lim->features &= ~BLK_FEAT_FUA;
 
+	blk_validate_atomic_write_limits(lim);
+
 	err = blk_validate_integrity_limits(lim);
 	if (err)
 		return err;