1 files changed, 96 insertions, 0 deletions

diff --git a/Documentation/prctl/disable-tsc-ctxt-sw-stress-test.c b/Documentation/prctl/disable-tsc-ctxt-sw-stress-test.c
new file mode 100644
index 000000000000..f8e8e95e81fd
--- /dev/null
+++ b/Documentation/prctl/disable-tsc-ctxt-sw-stress-test.c
@@ -0,0 +1,96 @@
+/*
+ * Tests for prctl(PR_GET_TSC, ...) / prctl(PR_SET_TSC, ...)
+ *
+ * Tests if the control register is updated correctly
+ * at context switches
+ *
+ * Warning: this test will cause a very high load for a few seconds
+ *
+ */
+
+#include <stdio.h>
+#include <stdlib.h>
+#include <unistd.h>
+#include <signal.h>
+#include <inttypes.h>
+#include <wait.h>
+
+
+#include <sys/prctl.h>
+#include <linux/prctl.h>
+
+/* Get/set the process' ability to use the timestamp counter instruction */
+#ifndef PR_GET_TSC
+#define PR_GET_TSC 25
+#define PR_SET_TSC 26
+# define PR_TSC_ENABLE          1   /* allow the use of the timestamp counter */
+# define PR_TSC_SIGSEGV         2   /* throw a SIGSEGV instead of reading the TSC */
+#endif
+
+uint64_t rdtsc() {
+uint32_t lo, hi;
+/* We cannot use "=A", since this would use %rax on x86_64 */
+__asm__ __volatile__ ("rdtsc" : "=a" (lo), "=d" (hi));
+return (uint64_t)hi << 32 | lo;
+}
+
+void sigsegv_expect(int sig)
+{
+        /* */
+}
+
+void segvtask(void)
+{
+        if (prctl(PR_SET_TSC, PR_TSC_SIGSEGV) < 0)
+        {
+                perror("prctl");
+                exit(0);
+        }
+        signal(SIGSEGV, sigsegv_expect);
+        alarm(10);
+        rdtsc();
+        fprintf(stderr, "FATAL ERROR, rdtsc() succeeded while disabled\n");
+        exit(0);
+}
+
+
+void sigsegv_fail(int sig)
+{
+        fprintf(stderr, "FATAL ERROR, rdtsc() failed while enabled\n");
+        exit(0);
+}
+
+void rdtsctask(void)
+{
+        if (prctl(PR_SET_TSC, PR_TSC_ENABLE) < 0)
+        {
+                perror("prctl");
+                exit(0);
+        }
+        signal(SIGSEGV, sigsegv_fail);
+        alarm(10);
+        for(;;) rdtsc();
+}
+
+
+int main(int argc, char **argv)
+{
+        int n_tasks = 100, i;
+
+        fprintf(stderr, "[No further output means we're allright]\n");
+
+        for (i=0; i<n_tasks; i++)
+                if (fork() == 0)
+                {
+                        if (i & 1)
+                                segvtask();
+                        else
+                                rdtsctask();
+                }
+
+        for (i=0; i<n_tasks; i++)
+                wait(NULL);
+
+        exit(0);
+}
+