git.ipfire.org Git - thirdparty/kernel/stable-queue.git/blob

   1 From 27e99ade81368e6fdda3212bff9345177cf9e57a Mon Sep 17 00:00:00 2001
   2 From: Wang Sen <senwang@linux.vnet.ibm.com>
   3 Date: Mon, 30 Jul 2012 14:25:06 +0800
   4 Subject: SCSI: scsi: virtio-scsi: Fix address translation failure of HighMem pages used by sg list
   5
   6 From: Wang Sen <senwang@linux.vnet.ibm.com>
   7
   8 commit 27e99ade81368e6fdda3212bff9345177cf9e57a upstream.
   9
  10 When using the commands below to write some data to a virtio-scsi LUN of the
  11 QEMU guest(32-bit) with 1G physical memory(qemu -m 1024), the qemu will crash.
  12
  13         # sudo mkfs.ext4 /dev/sdb  (/dev/sdb is the virtio-scsi LUN.)
  14         # sudo mount /dev/sdb /mnt
  15         # dd if=/dev/zero of=/mnt/file bs=1M count=1024
  16
  17 In current implementation, sg_set_buf is called to add buffers to sg list which
  18 is put into the virtqueue eventually. But if there are some HighMem pages in
  19 table->sgl you can not get virtual address by sg_virt. So, sg_virt(sg_elem) may
  20 return NULL value. This will cause QEMU exit when virtqueue_map_sg is called
  21 in QEMU because an invalid GPA is passed by virtqueue.
  22
  23 Two solutions are discussed here:
  24 http://lkml.indiana.edu/hypermail/linux/kernel/1207.3/00675.html
  25
  26 Finally, value assignment approach was adopted because:
  27
  28 Value assignment creates a well-formed scatterlist, because the termination
  29 marker in source sg_list has been set in blk_rq_map_sg(). The last entry of the
  30 source sg_list is just copied to the the last entry in destination list.  Note
  31 that, for now, virtio_ring does not care about the form of the scatterlist and
  32 simply processes the first out_num + in_num consecutive elements of the sg[]
  33 array.
  34
  35 I have tested the patch on my workstation. QEMU would not crash any more.
  36
  37 Signed-off-by: Wang Sen <senwang@linux.vnet.ibm.com>
  38 Acked-by: Paolo Bonzini <pbonzini@redhat.com>
  39 Signed-off-by: James Bottomley <JBottomley@Parallels.com>
  40 Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
  41
  42 ---
  43  drivers/scsi/virtio_scsi.c |    2 +-
  44  1 file changed, 1 insertion(+), 1 deletion(-)
  45
  46 --- a/drivers/scsi/virtio_scsi.c
  47 +++ b/drivers/scsi/virtio_scsi.c
  48 @@ -198,7 +198,7 @@ static void virtscsi_map_sgl(struct scat
  49         int i;
  50
  51         for_each_sg(table->sgl, sg_elem, table->nents, i)
  52 -               sg_set_buf(&sg[idx++], sg_virt(sg_elem), sg_elem->length);
  53 +               sg[idx++] = *sg_elem;
  54
  55         *p_idx = idx;
  56  }