dm: bounce_pfn limit added

[Vasily Averin <vvs@sw.ru>]

Device mapper uses its own bounce_pfn that may differ from one on underlying
device. In that way dm can build incorrect requests that contain sg elements
greater than underlying device is able to handle.

This is the cause of slab corruption in i2o layer, occurred on i386 arch when
very long direct IO requests are addressed to dm-over-i2o device.

Signed-off-by:	Vasily Averin <vvs@sw.ru>

--- a/drivers/md/dm-table.c
+++ b/drivers/md/dm-table.c
@@ -102,6 +102,8 @@ static void combine_restrictions_low(struct io_restrictions
 	lhs->seg_boundary_mask =
 		min_not_zero(lhs->seg_boundary_mask, rhs->seg_boundary_mask);

+	lhs->bounce_pfn = min_not_zero(lhs->bounce_pfn, rhs->bounce_pfn);
+
 	lhs->no_cluster |= rhs->no_cluster;
 }

@@ -566,6 +568,8 @@ void dm_set_device_limits(struct dm_target *ti, struct
 		min_not_zero(rs->seg_boundary_mask,
 			     q->seg_boundary_mask);

+	rs->bounce_pfn = min_not_zero(rs->bounce_pfn, q->bounce_pfn);
+
 	rs->no_cluster |= !test_bit(QUEUE_FLAG_CLUSTER, &q->queue_flags);
 }
 EXPORT_SYMBOL_GPL(dm_set_device_limits);
@@ -707,6 +711,8 @@ static void check_for_valid_limits(struct io_restrictions
 		rs->max_segment_size = MAX_SEGMENT_SIZE;
 	if (!rs->seg_boundary_mask)
 		rs->seg_boundary_mask = -1;
+	if (!rs->bounce_pfn)
+		rs->bounce_pfn = -1;
 }

 int dm_table_add_target(struct dm_table *t, const char *type,
@@ -891,6 +897,7 @@ void dm_table_set_restrictions(struct dm_table *t, struct
 	q->hardsect_size = t->limits.hardsect_size;
 	q->max_segment_size = t->limits.max_segment_size;
 	q->seg_boundary_mask = t->limits.seg_boundary_mask;
+	q->bounce_pfn = t->limits.bounce_pfn;
 	if (t->limits.no_cluster)
 		q->queue_flags &= ~(1 << QUEUE_FLAG_CLUSTER);
 	else
--- a/include/linux/device-mapper.h
+++ b/include/linux/device-mapper.h
@@ -111,6 +111,7 @@ struct target_type {

 struct io_restrictions {
 	unsigned long		seg_boundary_mask;
+	unsigned long		bounce_pfn;
 	unsigned int		max_sectors;
 	unsigned int		max_segment_size;
 	unsigned short		max_phys_segments;