On Mon, Jul 30, 2012 at 02:25:06PM +0800, Wang Sen wrote:
> 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.
>
> Cc: <[email protected]> # 3.4: 4fe74b1: [SCSI] virtio-scsi: SCSI driver
> Signed-off-by: Wang Sen <[email protected]>
> ---
> 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 1b38431..6661610 100644
> --- a/drivers/scsi/virtio_scsi.c
> +++ b/drivers/scsi/virtio_scsi.c
> @@ -198,7 +198,7 @@ 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;
> }
> --
> 1.7.9.5
Paolo has acked and no further issues have been raised.
James: Can this be merged?
Stefan