[kvm-unit-tests,v1] s390x: try multiple times to stop CPU

Commit Message

David Hildenbrand Sept. 20, 2017, 4:25 p.m. UTC

In theory, we could get a CC == 3, meaning the SIGP facility is busy
and we have to retry. So let's retry quite a number of times and
at least print a message about the problem before going into a safe loop.

Signed-off-by: David Hildenbrand <[e-mail]>
---

While working on TCG SMP support, I had a BUG whereby the CPU would
not directly stop but cotinue running for some instructions. This should
no properly detect such scenarios where the CPU keeps running after the
SIGP without indicating CC=3.

 lib/s390x/io.c | 31 +++++++++++++++++++++++++++----
 1 file changed, 27 insertions(+), 4 deletions(-)

Comments

David Hildenbrand Sept. 20, 2017, 8:11 p.m. UTC | #1

> +static void machine_stop(void)
> +{
> +	int retry = 999999;
> +	int cc;
> +
> +	/* for now we only have 1 CPU to stop */
> +	do {
> +		cc = sigp_stop();
> +		retry--;
> +	} while (cc == 3 && retry);

This should be 2 instead of 3 ... but I am currently working on SIGP
tests and plan to introduce defines for all these, so this patch can wait.

Patch

diff --git a/lib/s390x/io.c b/lib/s390x/io.c
index 12f9d26..c48d6b1 100644
--- a/lib/s390x/io.c
+++ b/lib/s390x/io.c
@@ -14,6 +14,7 @@ 
 #include <argv.h>
 #include <asm/spinlock.h>
 #include <asm/facility.h>
+#include <asm/barrier.h>
 #include "sclp.h"
 
 extern char ipl_args[];
@@ -28,14 +29,36 @@  void puts(const char *s)
 	spin_unlock(&lock);
 }
 
-static void sigp_stop()
+static int sigp_stop(void)
 {
 	register unsigned long status asm ("1") = 0;
 	register unsigned long cpu asm ("2") = 0;
+	int cc;
 
 	asm volatile(
-		"	sigp %0,%1,0(%2)\n"
-		: "+d" (status)  : "d" (cpu), "d" (5) : "cc");
+		"	sigp %1,%2,0(%3)\n"
+		"	ipm %0\n"
+		"	srl %0,28\n"
+		: "=d" (cc), "+d" (status) : "d" (cpu), "d" (5) : "cc");
+	return cc;
+}
+
+static void machine_stop(void)
+{
+	int retry = 999999;
+	int cc;
+
+	/* for now we only have 1 CPU to stop */
+	do {
+		cc = sigp_stop();
+		retry--;
+	} while (cc == 3 && retry);
+
+	printf("\nERROR: Could not stop CPU(s)\n");
+	printf("\nEXIT: STATUS=-1\n");
+	while (true) {
+		mb();
+	}
 }
 
 void setup()
@@ -48,5 +71,5 @@  void setup()
 void exit(int code)
 {
 	printf("\nEXIT: STATUS=%d\n", ((code) << 1) | 1);
-	sigp_stop();
+	machine_stop();
 }