[kvm-unit-tests PATCH] s390x: Workaround smp stop and store status race

[Janosch Frank <frankja@linux.ibm.com>]

KVM and QEMU handle a SIGP stop and store status in two steps:
1) Stop the CPU by injecting a stop request
2) Store when the CPU has left SIE because of the stop request

The problem is that the SIGP order is already considered completed by
KVM/QEMU when step 1 has been performed and not once both have
completed. In addition we currently don't implement the busy CC so a
kernel has no way of knowing that the store has finished other than
checking the location for the store.

This workaround is based on the fact that for a new SIE entry (via the
added smp restart) a stop with the store status has to be finished
first.

Correct handling of this in KVM/QEMU will need some thought and time.

Signed-off-by: Janosch Frank <frankja@linux.ibm.com>
---
 s390x/smp.c | 5 ++++-
 1 file changed, 4 insertions(+), 1 deletion(-)

diff --git a/s390x/smp.c b/s390x/smp.c
index b0ece491..32f284a2 100644
--- a/s390x/smp.c
+++ b/s390x/smp.c
@@ -102,12 +102,15 @@ static void test_stop_store_status(void)
 	lc->grs_sa[15] = 0;
 	smp_cpu_stop_store_status(1);
 	mb();
+	report(smp_cpu_stopped(1), "cpu stopped");
+	/* For the cpu to be started it should have finished storing */
+	smp_cpu_restart(1);
 	report(lc->prefix_sa == (uint32_t)(uintptr_t)cpu->lowcore, "prefix");
 	report(lc->grs_sa[15], "stack");
-	report(smp_cpu_stopped(1), "cpu stopped");
 	report_prefix_pop();
 
 	report_prefix_push("stopped");
+	smp_cpu_stop(1);
 	lc->prefix_sa = 0;
 	lc->grs_sa[15] = 0;
 	smp_cpu_stop_store_status(1);
-- 
2.25.1