From: Wang Sen Date: Mon, 30 Jul 2012 14:25:06 +0800 Subject: [09/12] [SCSI] scsi: virtio-scsi: Fix address translation failure of HighMem pages used by sg list commit 27e99ade81368e6fdda3212bff9345177cf9e57a upstream. When using the commands below to write some data to a virtio-scsi LUN of the QEMU guest(32-bit) with 1G physical memory(qemu -m 1024), the qemu will crash. # sudo mkfs.ext4 /dev/sdb (/dev/sdb is the virtio-scsi LUN.) # sudo mount /dev/sdb /mnt # dd if=/dev/zero of=/mnt/file bs=1M count=1024 In current implementation, sg_set_buf is called to add buffers to sg list which is put into the virtqueue eventually. But if there are some HighMem pages in table->sgl you can not get virtual address by sg_virt. So, sg_virt(sg_elem) may return NULL value. This will cause QEMU exit when virtqueue_map_sg is called in QEMU because an invalid GPA is passed by virtqueue. Two solutions are discussed here: http://lkml.indiana.edu/hypermail/linux/kernel/1207.3/00675.html Finally, value assignment approach was adopted because: Value assignment creates a well-formed scatterlist, because the termination marker in source sg_list has been set in blk_rq_map_sg(). The last entry of the source sg_list is just copied to the the last entry in destination list. Note that, for now, virtio_ring does not care about the form of the scatterlist and simply processes the first out_num + in_num consecutive elements of the sg[] array. I have tested the patch on my workstation. QEMU would not crash any more. Signed-off-by: Wang Sen Acked-by: Paolo Bonzini Signed-off-by: James Bottomley --- drivers/scsi/virtio_scsi.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) diff --git a/drivers/scsi/virtio_scsi.c b/drivers/scsi/virtio_scsi.c index c7030fb..3e79a2f 100644 --- a/drivers/scsi/virtio_scsi.c +++ b/drivers/scsi/virtio_scsi.c @@ -331,7 +331,7 @@ static void virtscsi_map_sgl(struct scatterlist *sg, unsigned int *p_idx, int i; for_each_sg(table->sgl, sg_elem, table->nents, i) - sg_set_buf(&sg[idx++], sg_virt(sg_elem), sg_elem->length); + sg[idx++] = *sg_elem; *p_idx = idx; }