Re: [PATCH v1 1/1] s390x: css: report errors from ccw_dstream_read/write

[Cornelia Huck <cohuck@redhat.com>]

On Tue,  6 Apr 2021 09:44:13 +0200
Pierre Morel <pmorel@linux.ibm.com> wrote:

> ccw_dstream_read/write functions returned values are sometime
> not taking into account and reported back to the upper level
> of interpretation of CCW instructions.
> 
> It follows that accessing an invalid address does not trigger
> a subchannel status program check to the guest as it should.
> 
> Let's test the return values of ccw_dstream_write[_buf] and
> ccw_dstream_read[_buf] and report it to the caller.

Yes, checking/propagating the return code is something that was missing
in several places.

> 
> Signed-off-by: Pierre Morel <pmorel@linux.ibm.com>
> ---
>  hw/char/terminal3270.c | 11 +++++--
>  hw/s390x/3270-ccw.c    |  3 ++
>  hw/s390x/css.c         | 16 +++++-----
>  hw/s390x/virtio-ccw.c  | 66 ++++++++++++++++++++++++++++++------------
>  4 files changed, 69 insertions(+), 27 deletions(-)
> 
> diff --git a/hw/char/terminal3270.c b/hw/char/terminal3270.c
> index a9a46c8ed3..82e85fac2e 100644
> --- a/hw/char/terminal3270.c
> +++ b/hw/char/terminal3270.c
> @@ -200,9 +200,13 @@ static int read_payload_3270(EmulatedCcw3270Device *dev)
>  {
>      Terminal3270 *t = TERMINAL_3270(dev);
>      int len;
> +    int ret;
>  
>      len = MIN(ccw_dstream_avail(get_cds(t)), t->in_len);
> -    ccw_dstream_write_buf(get_cds(t), t->inv, len);
> +    ret = ccw_dstream_write_buf(get_cds(t), t->inv, len);
> +    if (ret < 0) {
> +        return ret;
> +    }

This looks correct: together with the change below, you end up
propagating a negative error value to the ccw callback handling.

>      t->in_len -= len;
>  
>      return len;
> @@ -260,7 +264,10 @@ static int write_payload_3270(EmulatedCcw3270Device *dev, uint8_t cmd)
>  
>      t->outv[out_len++] = cmd;
>      do {
> -        ccw_dstream_read_buf(get_cds(t), &t->outv[out_len], len);
> +        retval = ccw_dstream_read_buf(get_cds(t), &t->outv[out_len], len);
> +        if (retval < 0) {
> +            return retval;

Here, however, I'm not sure. Returning a negative error here is fine,
but handle_payload_3270_write (not changed in this patch) seems to
match everything to -EIO. Shouldn't it just be propagated, and maybe 0
mapped to -EIO only? If I'm not confused, we'll end up mapping every
error to intervention required.

> +        }
>          count = ccw_dstream_avail(get_cds(t));
>          out_len += len;
>  
> diff --git a/hw/s390x/3270-ccw.c b/hw/s390x/3270-ccw.c
> index 821319eee6..cc1371f01c 100644
> --- a/hw/s390x/3270-ccw.c
> +++ b/hw/s390x/3270-ccw.c
> @@ -31,6 +31,9 @@ static int handle_payload_3270_read(EmulatedCcw3270Device *dev, CCW1 *ccw)
>      }
>  
>      len = ck->read_payload_3270(dev);
> +    if (len < 0) {
> +        return len;
> +    }
>      ccw_dev->sch->curr_status.scsw.count = ccw->count - len;
>  
>      return 0;
> diff --git a/hw/s390x/css.c b/hw/s390x/css.c
> index fe47751df4..99e476f193 100644
> --- a/hw/s390x/css.c
> +++ b/hw/s390x/css.c
> @@ -1055,10 +1055,11 @@ static int css_interpret_ccw(SubchDev *sch, hwaddr ccw_addr,
>              }
>          }
>          len = MIN(ccw.count, sizeof(sch->sense_data));
> -        ccw_dstream_write_buf(&sch->cds, sch->sense_data, len);
> -        sch->curr_status.scsw.count = ccw_dstream_residual_count(&sch->cds);
> -        memset(sch->sense_data, 0, sizeof(sch->sense_data));
> -        ret = 0;
> +        ret = ccw_dstream_write_buf(&sch->cds, sch->sense_data, len);
> +        if (!ret) {
> +            sch->curr_status.scsw.count = ccw_dstream_residual_count(&sch->cds);

I'm wondering about the residual count here. Table 16-7 "Contents of
Count Field in SCSW" in the PoP looks a bit more complicated for some
error conditions, especially if IDALs are involved. Not sure if we
should attempt to write something to count in those conditions; but on
the other hand, I don't think our error conditions are as complex
anyway, and we can make this simplification.

> +            memset(sch->sense_data, 0, sizeof(sch->sense_data));
> +        }
>          break;
>      case CCW_CMD_SENSE_ID:
>      {
> @@ -1083,9 +1084,10 @@ static int css_interpret_ccw(SubchDev *sch, hwaddr ccw_addr,
>          } else {
>              sense_id[0] = 0;
>          }
> -        ccw_dstream_write_buf(&sch->cds, sense_id, len);
> -        sch->curr_status.scsw.count = ccw_dstream_residual_count(&sch->cds);
> -        ret = 0;
> +        ret = ccw_dstream_write_buf(&sch->cds, sense_id, len);
> +        if (!ret) {
> +            sch->curr_status.scsw.count = ccw_dstream_residual_count(&sch->cds);
> +        }
>          break;
>      }
>      case CCW_CMD_TIC:

(...)

Otherwise, looks good.