Re: [PATCH v2 1/7] s390/cio: Update SCSW if it points to the end of the chain

Farhan Ali
2019-05-15T14:30:43Z

On 05/14/2019 07:42 PM, Eric Farman wrote:
> Per the POPs [1], when processing an interrupt the SCSW.CPA field of an
> IRB generally points to 8 bytes after the last CCW that was executed
> (there are exceptions, but this is the most common behavior).
>
> In the case of an error, this points us to the first un-executed CCW
> in the chain. But in the case of normal I/O, the address points beyond
> the end of the chain. While the guest generally only cares about this
> when possibly restarting a channel program after error recovery, we
> should convert the address even in the good scenario so that we provide
> a consistent, valid, response upon I/O completion.
>
> [1] Figure 16-6 in SA22-7832-11. The footnotes in that table also state
> that this is true even if the resulting address is invalid or protected,
> but moving to the end of the guest chain should not be a surprise.
>
> Signed-off-by: Eric Farman <farman@linux.ibm.com>
> ---
> drivers/s390/cio/vfio_ccw_cp.c | 6 +++++-
> 1 file changed, 5 insertions(+), 1 deletion(-)
>
> diff --git a/drivers/s390/cio/vfio_ccw_cp.c b/drivers/s390/cio/vfio_ccw_cp.c
> index 384b3987eeb4..41f48b8790bc 100644
> --- a/drivers/s390/cio/vfio_ccw_cp.c
> +++ b/drivers/s390/cio/vfio_ccw_cp.c
> @@ -870,7 +870,11 @@ void cp_update_scsw(struct channel_program *cp, union scsw *scsw)
> */
> list_for_each_entry(chain, &cp->ccwchain_list, next) {
> ccw_head = (u32)(u64)chain->ch_ccw;
> - if (is_cpa_within_range(cpa, ccw_head, chain->ch_len)) {
> + /*
> + * On successful execution, cpa points just beyond the end
> + * of the chain.
> + */
> + if (is_cpa_within_range(cpa, ccw_head, chain->ch_len + 1)) {
> /*
> * (cpa - ccw_head) is the offset value of the host
> * physical ccw to its chain head.
>

Reviewed-by: Farhan Ali <alifm@linux.ibm.com>