vdpa_sim_blk: allocate the buffer zeroed

Deleting and recreating a device can lead to having the same
content as the old device, so let's always allocate buffers
completely zeroed out.

Fixes: abebb16 ("vdpa_sim_blk: support shared backend")
Suggested-by: Qing Wang <qinwang@redhat.com>
Signed-off-by: Stefano Garzarella <sgarzare@redhat.com>
Message-Id: <20231031144339.121453-1-sgarzare@redhat.com>
Signed-off-by: Michael S. Tsirkin <mst@redhat.com>
Acked-by: Eugenio Pérez <eperezma@redhat.com>
Acked-by: Jason Wang <jasowang@redhat.com>

Author: stefano-garzarella

drivers/vdpa/vdpa_sim/vdpa_sim_blk.c

@@ -437,7 +437,7 @@ static int vdpasim_blk_dev_add(struct vdpa_mgmt_dev *mdev, const char *name,
 	if (blk->shared_backend) {
 		blk->buffer = shared_buffer;
 	} else {
-		blk->buffer = kvmalloc(VDPASIM_BLK_CAPACITY << SECTOR_SHIFT,
+		blk->buffer = kvzalloc(VDPASIM_BLK_CAPACITY << SECTOR_SHIFT,
 				       GFP_KERNEL);
 		if (!blk->buffer) {
 			ret = -ENOMEM;
@@ -495,7 +495,7 @@ static int __init vdpasim_blk_init(void)
 		goto parent_err;
 
 	if (shared_backend) {
-		shared_buffer = kvmalloc(VDPASIM_BLK_CAPACITY << SECTOR_SHIFT,
+		shared_buffer = kvzalloc(VDPASIM_BLK_CAPACITY << SECTOR_SHIFT,
 					 GFP_KERNEL);
 		if (!shared_buffer) {
 			ret = -ENOMEM;