[kvm-unit-tests PULL 6/9] s390x: smp: Rework cpu start and active tracking

[Thomas Huth <thuth@redhat.com>]

From: Janosch Frank <frankja@linux.ibm.com>

The architecture specifies that processing sigp orders may be
asynchronous, and this is indeed the case on some hypervisors, so we
need to wait until the cpu runs before we return from the setup/start
function.

As there was a lot of duplicate code, a common function for cpu
restarts has been introduced.

Signed-off-by: Janosch Frank <frankja@linux.ibm.com>
Reviewed-by: Cornelia Huck <cohuck@redhat.com>
Message-Id: <20200201152851.82867-7-frankja@linux.ibm.com>
Reviewed-by: Thomas Huth <thuth@redhat.com>
Signed-off-by: Thomas Huth <thuth@redhat.com>
---
 lib/s390x/smp.c | 56 ++++++++++++++++++++++++++++++-------------------
 1 file changed, 35 insertions(+), 21 deletions(-)

diff --git a/lib/s390x/smp.c b/lib/s390x/smp.c
index f57f420..4578003 100644
--- a/lib/s390x/smp.c
+++ b/lib/s390x/smp.c
@@ -104,35 +104,52 @@ int smp_cpu_stop_store_status(uint16_t addr)
 	return rc;
 }
 
+static int smp_cpu_restart_nolock(uint16_t addr, struct psw *psw)
+{
+	int rc;
+	struct cpu *cpu = smp_cpu_from_addr(addr);
+
+	if (!cpu)
+		return -1;
+	if (psw) {
+		cpu->lowcore->restart_new_psw.mask = psw->mask;
+		cpu->lowcore->restart_new_psw.addr = psw->addr;
+	}
+	/*
+	 * Stop the cpu, so we don't have a race between a running cpu
+	 * and the restart in the test that checks if the cpu is
+	 * running after the restart.
+	 */
+	smp_cpu_stop_nolock(addr, false);
+	rc = sigp(addr, SIGP_RESTART, 0, NULL);
+	if (rc)
+		return rc;
+	/*
+	 * The order has been accepted, but the actual restart may not
+	 * have been performed yet, so wait until the cpu is running.
+	 */
+	while (!smp_cpu_running(addr))
+		mb();
+	cpu->active = true;
+	return 0;
+}
+
 int smp_cpu_restart(uint16_t addr)
 {
-	int rc = -1;
-	struct cpu *cpu;
+	int rc;
 
 	spin_lock(&lock);
-	cpu = smp_cpu_from_addr(addr);
-	if (cpu) {
-		rc = sigp(addr, SIGP_RESTART, 0, NULL);
-		cpu->active = true;
-	}
+	rc = smp_cpu_restart_nolock(addr, NULL);
 	spin_unlock(&lock);
 	return rc;
 }
 
 int smp_cpu_start(uint16_t addr, struct psw psw)
 {
-	int rc = -1;
-	struct cpu *cpu;
-	struct lowcore *lc;
+	int rc;
 
 	spin_lock(&lock);
-	cpu = smp_cpu_from_addr(addr);
-	if (cpu) {
-		lc = cpu->lowcore;
-		lc->restart_new_psw.mask = psw.mask;
-		lc->restart_new_psw.addr = psw.addr;
-		rc = sigp(addr, SIGP_RESTART, 0, NULL);
-	}
+	rc = smp_cpu_restart_nolock(addr, &psw);
 	spin_unlock(&lock);
 	return rc;
 }
@@ -192,10 +209,7 @@ int smp_cpu_setup(uint16_t addr, struct psw psw)
 	lc->sw_int_crs[0] = 0x0000000000040000UL;
 
 	/* Start processing */
-	rc = sigp_retry(cpu->addr, SIGP_RESTART, 0, NULL);
-	if (!rc)
-		cpu->active = true;
-
+	smp_cpu_restart_nolock(addr, NULL);
 out:
 	spin_unlock(&lock);
 	return rc;
-- 
2.18.1