On Thu, Sep 06, 2018 at 01:37:19PM -0700, Xuewei Zhang wrote:
> Currently a scsi device won't contribute to kernel randomness when it
> uses blk-mq. Since we commonly use scsi on rotational device with
> blk-mq, it make sense to keep contributing to kernel randomness in these
> cases. This is especially important for virtual machines.
>
> commit b5b6e8c8d3b4 ("scsi: virtio_scsi: fix IO hang caused by automatic
> irq vector affinity") made all virtio-scsi device to use blk-mq, which
> does not contribute to randomness today. So for a virtual machine only
> having virtio-scsi disk (which is common), it will simple stop getting
> randomness from its disks in today's implementation.
>
> With this patch, if the above VM has rotational virtio-scsi device, then
> it can still benefit from the entropy generated from the disk.
>
> Reported-by: Xuewei Zhang <xueweiz@xxxxxxxxxx>
> Signed-off-by: Xuewei Zhang <xueweiz@xxxxxxxxxx>
> ---
> drivers/scsi/sd.c | 3 +++
> 1 file changed, 3 insertions(+)
>
> diff --git a/drivers/scsi/sd.c b/drivers/scsi/sd.c
> index b79b366a94f7..5e4f10d28065 100644
> --- a/drivers/scsi/sd.c
> +++ b/drivers/scsi/sd.c
> @@ -2959,6 +2959,9 @@ static void sd_read_block_characteristics(struct scsi_disk *sdkp)
> if (rot == 1) {
> blk_queue_flag_set(QUEUE_FLAG_NONROT, q);
> blk_queue_flag_clear(QUEUE_FLAG_ADD_RANDOM, q);
> + } else {
> + blk_queue_flag_clear(QUEUE_FLAG_NONROT, q);
> + blk_queue_flag_set(QUEUE_FLAG_ADD_RANDOM, q);
> }
>
> if (sdkp->device->type == TYPE_ZBC) {
> --
> 2.19.0.rc2.392.g5ba43deb5a-goog
>
Look reasonable, especially the disk randomness is added by SCSI itself.
Reviewed-by: Ming Lei <ming.lei@xxxxxxxxxx>
Thanks,
Ming
