selftests/powerpc: Add a test of spectre_v2 mitigations

This test uses the PMU to count branch prediction hits/misses for a
known loop, and compare the result to the reported spectre v2
mitigation.

This gives us a way of sanity checking that the reported mitigation is
actually in effect.

Sample output for some cases, eg:

  Power9:
    sysfs reports: 'Vulnerable'
     PM_BR_PRED_CCACHE: result        368 running/enabled 5792777124
    PM_BR_MPRED_CCACHE: result        319 running/enabled 5792775546
     PM_BR_PRED_PCACHE: result 2147483281 running/enabled 5792773128
    PM_BR_MPRED_PCACHE: result  213604201 running/enabled 5792771640
    Miss percent 9 %
    OK - Measured branch prediction rates match reported spectre v2 mitigation.

    sysfs reports: 'Mitigation: Indirect branch serialisation (kernel only)'
     PM_BR_PRED_CCACHE: result        895 running/enabled 5780320920
    PM_BR_MPRED_CCACHE: result        822 running/enabled 5780312414
     PM_BR_PRED_PCACHE: result 2147482754 running/enabled 5780308836
    PM_BR_MPRED_PCACHE: result  213639731 running/enabled 5780307912
    Miss percent 9 %
    OK - Measured branch prediction rates match reported spectre v2 mitigation.

    sysfs reports: 'Mitigation: Indirect branch cache disabled'
     PM_BR_PRED_CCACHE: result 2147483649 running/enabled 20540186160
    PM_BR_MPRED_CCACHE: result 2147483649 running/enabled 20540180056
     PM_BR_PRED_PCACHE: result          0 running/enabled 20540176090
    PM_BR_MPRED_PCACHE: result          0 running/enabled 20540174182
    Miss percent 100 %
    OK - Measured branch prediction rates match reported spectre v2 mitigation.

  Power8:
    sysfs reports: 'Vulnerable'
     PM_BR_PRED_CCACHE: result 2147483649 running/enabled 3505888142
    PM_BR_MPRED_CCACHE: result          9 running/enabled 3505882788
    Miss percent 0 %
    OK - Measured branch prediction rates match reported spectre v2 mitigation.

    sysfs reports: 'Mitigation: Indirect branch cache disabled'
     PM_BR_PRED_CCACHE: result 2147483649 running/enabled 16931421988
    PM_BR_MPRED_CCACHE: result 2147483649 running/enabled 16931416478
    Miss percent 100 %
    OK - Measured branch prediction rates match reported spectre v2 mitigation.
    success: spectre_v2

Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Link: https://lore.kernel.org/r/20190520105520.22274-1-mpe@ellerman.id.au

1 files changed, 20 insertions, 0 deletions

diff --git a/tools/testing/selftests/powerpc/utils.c b/tools/testing/selftests/powerpc/utils.c
index c02d24835db4..5ee0e98c4896 100644
--- a/tools/testing/selftests/powerpc/utils.c
+++ b/tools/testing/selftests/powerpc/utils.c
@@ -127,6 +127,26 @@ bool is_ppc64le(void)
 	return strcmp(uts.machine, "ppc64le") == 0;
 }
 
+int read_sysfs_file(char *fpath, char *result, size_t result_size)
+{
+	char path[PATH_MAX] = "/sys/";
+	int rc = -1, fd;
+
+	strncat(path, fpath, PATH_MAX - strlen(path) - 1);
+
+	if ((fd = open(path, O_RDONLY)) < 0)
+		return rc;
+
+	rc = read(fd, result, result_size);
+
+	close(fd);
+
+	if (rc < 0)
+		return rc;
+
+	return 0;
+}
+
 int read_debugfs_file(char *debugfs_file, int *result)
 {
 	int rc = -1, fd;