Re: [kvm-unit-tests PATCH v3 7/9] s390x: css: msch, enable test

Cornelia Huck
2019-12-10T09:10:03Z

On Tue, 10 Dec 2019 10:01:46 +0100
Pierre Morel <pmorel@linux.ibm.com> wrote:

> On 2019-12-09 17:54, Cornelia Huck wrote:
> > On Fri, 6 Dec 2019 17:26:26 +0100
> > Pierre Morel <pmorel@linux.ibm.com> wrote:
> >
> >> A second step when testing the channel subsystem is to prepare a channel
> >> for use.
> >> This includes:
> >> - Get the current SubCHannel Information Block (SCHIB) using STSCH
> >> - Update it in memory to set the ENABLE bit
> >> - Tell the CSS that the SCHIB has been modified using MSCH
> >> - Get the SCHIB from the CSS again to verify that the subchannel is
> >> enabled.
> >>
> >> This tests the success of the MSCH instruction by enabling a channel.
> >>
> >> Signed-off-by: Pierre Morel <pmorel@linux.ibm.com>
> >> ---
> >> s390x/css.c | 39 +++++++++++++++++++++++++++++++++++++++
> >> 1 file changed, 39 insertions(+)
> >>
> >> diff --git a/s390x/css.c b/s390x/css.c
> >> index 3d4a986..4c0031c 100644
> >> --- a/s390x/css.c
> >> +++ b/s390x/css.c
> >> @@ -58,11 +58,50 @@ static void test_enumerate(void)
> >> report("Tested %d devices, %d found", 1, scn, found);
> >> }
> >>
> >> +static void test_enable(void)
> >> +{
> >> + struct pmcw *pmcw = &schib.pmcw;
> >> + int cc;
> >> +
> >> + if (!test_device_sid) {
> >> + report_skip("No device");
> >> + return;
> >> + }
> >> + /* Read the SCIB for this subchannel */
> >
> > s/SCIB/SCHIB/
>
> yes
>
> >
> >> + cc = stsch(test_device_sid, &schib);
> >> + if (cc) {
> >> + report("stsch cc=%d", 0, cc);
> >> + return;
> >> + }
> >> + /* Update the SCHIB to enable the channel */
> >> + pmcw->flags |= PMCW_ENABLE;
> >> +
> >> + /* Tell the CSS we want to modify the subchannel */
> >> + cc = msch(test_device_sid, &schib);
> >> + if (cc) {
> >> + report("msch cc=%d", 0, cc);
> >
> > So you expect the subchannel to be idle? Probably true, especially as
> > QEMU has no reason to post an unsolicited interrupt for a test device.
> >
> >> + return;
> >> + }
> >> +
> >> + /* Read the SCHIB again to verify the enablement */
> >> + cc = stsch(test_device_sid, &schib);
> >> + if (cc) {
> >> + report("stsch cc=%d", 0, cc);
> >> + return;
> >> + }
> >> + if (!(pmcw->flags & PMCW_ENABLE)) {
> >> + report("Enable failed. pmcw: %x", 0, pmcw->flags);
> >
> > This check is fine when running under KVM. If this test is modified to
> > run under z/VM in the future, you probably should retry here: I've seen
> > the enable bit 'stick' only after the second msch() there.
>
> Oh. Thanks, may be I can loop with a delay and count.

FWIW, the Linux kernel code is trying 5 times.

> If I need to do this may be I need to create dedicated sub-functions to
> include the sanity tests.

I'm not sure how worthwhile investing time here is, actually: If you
don't plan to run under anything but KVM, you won't need it. I'm not
sure if current versions of z/VM still display the same behaviour (it
has been some time...); on the other hand, it is compliant with the
architecture...

>
> >
> >> + return;
> >> + }
> >> + report("Tested", 1);
> >> +}
> >> +
> >> static struct {
> >> const char *name;
> >> void (*func)(void);
> >> } tests[] = {
> >> { "enumerate (stsch)", test_enumerate },
> >> + { "enable (msch)", test_enable },
> >> { NULL, NULL }
> >> };
> >>
> >
>