Re: [Qemu-devel] [PATCH 1/2] s390x/ccs: add ccw-tester emulated device

[Cornelia Huck <cohuck@redhat.com>]

On Wed, 13 Sep 2017 15:27:51 +0200
Halil Pasic <pasic@linux.vnet.ibm.com> wrote:

> Add a fake device meant for testing the correctness of our css emulation.
> 
> What we currently have is writing a Fibonacci sequence of uint32_t to the
> device via ccw write. The write is going to fail if it ain't a Fibonacci
> and indicate a device exception in scsw together with the proper residual
> count.
> 
> Of course lot's of invalid inputs (besides basic data processing) can be
> tested with that as well.
> 
> Usage:
> 1) fire up a qemu with something like -device ccw-tester,devno=fe.0.0001
>    on the command line
> 2) exercise the device from the guest
> 
> Signed-off-by: Halil Pasic <pasic@linux.vnet.ibm.com>
> ---
> 
> Depends on the series 'add CCW indirect data access support'
> 
> ---
>  hw/s390x/Makefile.objs |   1 +
>  hw/s390x/ccw-tester.c  | 179 +++++++++++++++++++++++++++++++++++++++++++++++++
>  2 files changed, 180 insertions(+)
>  create mode 100644 hw/s390x/ccw-tester.c
> 

> +static int  ccw_tester_write_fib(SubchDev *sch, CCW1 ccw)
> +{
> +    CcwTesterDevice *d = sch->driver_data;
> +    bool is_fib = true;
> +    uint32_t sum;
> +    int ret = 0;
> +
> +    ccw_dstream_init(&sch->cds, &ccw, &sch->orb);
> +    d->fib.next = 0;
> +    while (ccw_dstream_avail(&sch->cds) > 0) {
> +        ret = ccw_dstream_read(&sch->cds,
> +                               d->fib.ring[abs_to_ring(d->fib.next)]);
> +        if (ret) {
> +            error(0, -ret, "fib");
> +            break;
> +        }
> +        if (d->fib.next > 2) {
> +            sum = (d->fib.ring[abs_to_ring(d->fib.next - 1)]
> +                  + d->fib.ring[abs_to_ring(d->fib.next - 2)]);
> +            is_fib = sum ==  d->fib.ring[abs_to_ring(d->fib.next)];

This is not endian-safe (noticed while testing on my laptop). Trivial
to fix:

diff --git a/hw/s390x/ccw-tester.c b/hw/s390x/ccw-tester.c
index c8017818c4..a425daaa34 100644
--- a/hw/s390x/ccw-tester.c
+++ b/hw/s390x/ccw-tester.c
@@ -58,9 +58,9 @@ static int  ccw_tester_write_fib(SubchDev *sch, CCW1 ccw)
             break;
         }
         if (d->fib.next > 2) {
-            sum = (d->fib.ring[abs_to_ring(d->fib.next - 1)]
-                  + d->fib.ring[abs_to_ring(d->fib.next - 2)]);
-            is_fib = sum ==  d->fib.ring[abs_to_ring(d->fib.next)];
+            sum = be32_to_cpu(d->fib.ring[abs_to_ring(d->fib.next - 1)])
+                + be32_to_cpu(d->fib.ring[abs_to_ring(d->fib.next - 2)]);
+            is_fib = sum == be32_to_cpu(d->fib.ring[abs_to_ring(d->fib.next)]);
             if (!is_fib) {
                 break;
             }

> +            if (!is_fib) {
> +                break;
> +            }
> +        }
> +        ++(d->fib.next);
> +    }
> +    if (!is_fib) {
> +        sch->curr_status.scsw.ctrl &= ~SCSW_ACTL_START_PEND;
> +        sch->curr_status.scsw.ctrl |= SCSW_STCTL_PRIMARY |
> +                                      SCSW_STCTL_SECONDARY |
> +                                      SCSW_STCTL_ALERT |
> +                                      SCSW_STCTL_STATUS_PEND;
> +        sch->curr_status.scsw.count = ccw_dstream_residual_count(&sch->cds);
> +        sch->curr_status.scsw.cpa = sch->channel_prog + 8;
> +        sch->curr_status.scsw.dstat =  SCSW_DSTAT_UNIT_EXCEP;
> +        return -EIO;
> +    }
> +    return ret;
> +}
> +
(...)
> +static Property ccw_tester_properties[] = {
> +    DEFINE_PROP_UINT16("cu_type", CcwTesterDevice, cu_type,
> +                        0x3831),

0x4711 would be nice :)

If we want to follow up on that testdev idea (and I think we should),
it might make sense to have a proper type reserve to prevent accidental
clashes.

(Or is there already something reserved for "hypervisor use" or
whatever?)

> +    DEFINE_PROP_UINT8("chpid_type", CcwTesterDevice, chpid_type,
> +                       0x98),
> +    DEFINE_PROP_END_OF_LIST(),
> +};

IIUC, pci-testdev provides some unit tests to testers (like kvm-tests)
itself. This might be an idea to follow up on for ccw as well.

There's quite some potential in this. We may want to make this a
permanent addition.