virtio_blk: fix handling single range discard request

mainline inclusion
from mainline-5.14-rc7
commit af822aa6
category: bugfix
bugzilla: https://gitee.com/openeuler/kernel/issues/I47ITN
CVE: NA

-------------------------------------------------

1f23816b ("virtio_blk: add discard and write zeroes support") starts
to support multi-range discard for virtio-blk. However, the virtio-blk
disk may report max discard segment as 1, at least that is exactly what
qemu is doing.

So far, block layer switches to normal request merge if max discard
segment
limit is 1, and multiple bios can be merged to single segment. This way
may
cause memory corruption in virtblk_setup_discard_write_zeroes().

Fix the issue by handling single max discard segment in straightforward
way.

Fixes: 1f23816b ("virtio_blk: add discard and write zeroes support")
Signed-off-by: NMing Lei <ming.lei@redhat.com>
Reviewed-by: NChristoph Hellwig <hch@lst.de>
Cc: Changpeng Liu <changpeng.liu@intel.com>
Cc: Daniel Verkamp <dverkamp@chromium.org>
Cc: Michael S. Tsirkin <mst@redhat.com>
Cc: Stefan Hajnoczi <stefanha@redhat.com>
Cc: Stefano Garzarella <sgarzare@redhat.com>
Signed-off-by: NJens Axboe <axboe@kernel.dk>
Signed-off-by: xuliqun <xuliqun@huayun.com>		# openEuler_contributor
Reviewed-by: NJason Yan <yanaijie@huawei.com>
Signed-off-by: NCheng Jian <cj.chengjian@huawei.com>

drivers/block/virtio_blk.c

@@ -204,6 +204,18 @@ static int virtblk_setup_discard_write_zeroes(struct request *req, bool unmap)
 	if (!range)
 		return -ENOMEM;
 
+	/*
+	 * Single max discard segment means multi-range discard isn't
+	 * supported, and block layer only runs contiguity merge like
+	 * normal RW request. So we can't reply on bio for retrieving
+	 * each range info.
+	 */
+	if (queue_max_discard_segments(req->q) == 1) {
+		range[0].flags = cpu_to_le32(flags);
+		range[0].num_sectors = cpu_to_le32(blk_rq_sectors(req));
+		range[0].sector = cpu_to_le64(blk_rq_pos(req));
+		n = 1;
+	} else {
 		__rq_for_each_bio(bio, req) {
 			u64 sector = bio->bi_iter.bi_sector;
 			u32 num_sectors = bio->bi_iter.bi_size >> SECTOR_SHIFT;
@@ -213,6 +225,9 @@ static int virtblk_setup_discard_write_zeroes(struct request *req, bool unmap)
 			range[n].sector = cpu_to_le64(sector);
 			n++;
 		}
+	}
+
+	WARN_ON_ONCE(n != segments);
 
 	req->special_vec.bv_page = virt_to_page(range);
 	req->special_vec.bv_offset = offset_in_page(range);