[V2 2/2] selftests/powerpc: EBB selftest for MMCR0 control for PMU SPRs in ISA v3.1

[Athira Rajeev <atrajeev@linux.vnet.ibm.com>]

With the MMCR0 control bit (PMCCEXT) in ISA v3.1, read access to
group B registers is restricted when MMCR0 PMCC=0b00. In other
platforms (like power9), the older behaviour works where group B
PMU SPRs are readable.

Patch creates a selftest which verifies that the test takes a
SIGILL when attempting to read PMU registers via helper function
"dump_ebb_state" for ISA v3.1.

Signed-off-by: Athira Rajeev <atrajeev@linux.vnet.ibm.com>
---
 tools/testing/selftests/powerpc/pmu/ebb/Makefile   |  2 +-
 .../powerpc/pmu/ebb/regs_access_pmccext_test.c     | 63 ++++++++++++++++++++++
 2 files changed, 64 insertions(+), 1 deletion(-)
 create mode 100644 tools/testing/selftests/powerpc/pmu/ebb/regs_access_pmccext_test.c

diff --git a/tools/testing/selftests/powerpc/pmu/ebb/Makefile b/tools/testing/selftests/powerpc/pmu/ebb/Makefile
index c5ecb46..0101606 100644
--- a/tools/testing/selftests/powerpc/pmu/ebb/Makefile
+++ b/tools/testing/selftests/powerpc/pmu/ebb/Makefile
@@ -24,7 +24,7 @@ TEST_GEN_PROGS := reg_access_test event_attributes_test cycles_test	\
 	 fork_cleanup_test ebb_on_child_test			\
 	 ebb_on_willing_child_test back_to_back_ebbs_test	\
 	 lost_exception_test no_handler_test			\
-	 cycles_with_mmcr2_test
+	 cycles_with_mmcr2_test regs_access_pmccext_test
 
 top_srcdir = ../../../../../..
 include ../../../lib.mk
diff --git a/tools/testing/selftests/powerpc/pmu/ebb/regs_access_pmccext_test.c b/tools/testing/selftests/powerpc/pmu/ebb/regs_access_pmccext_test.c
new file mode 100644
index 0000000..5f1a040
--- /dev/null
+++ b/tools/testing/selftests/powerpc/pmu/ebb/regs_access_pmccext_test.c
@@ -0,0 +1,63 @@
+// SPDX-License-Identifier: GPL-2.0-only
+/*
+ * Copyright 2021, Athira Rajeev, IBM Corp.
+ */
+
+#include <stdio.h>
+#include <stdlib.h>
+#include <setjmp.h>
+#include <signal.h>
+
+#include "ebb.h"
+
+
+/*
+ * Test that closing the EBB event clears MMCR0_PMCC and
+ * sets MMCR0_PMCCEXT preventing further read access to the
+ * group B PMU registers.
+ */
+
+static int regs_access_pmccext(void)
+{
+	struct event event;
+
+	SKIP_IF(!ebb_is_supported());
+
+	event_init_named(&event, 0x1001e, "cycles");
+	event_leader_ebb_init(&event);
+
+	FAIL_IF(event_open(&event));
+
+	ebb_enable_pmc_counting(1);
+	setup_ebb_handler(standard_ebb_callee);
+	ebb_global_enable();
+	FAIL_IF(ebb_event_enable(&event));
+
+	mtspr(SPRN_PMC1, pmc_sample_period(sample_period));
+
+	while (ebb_state.stats.ebb_count < 1)
+		FAIL_IF(core_busy_loop());
+
+	ebb_global_disable();
+	event_close(&event);
+
+	FAIL_IF(ebb_state.stats.ebb_count == 0);
+
+	/*
+	 * For ISA v3.1, verify the test takes a SIGILL when reading
+	 * PMU regs after the event is closed. With the control bit
+	 * in MMCR0 (PMCCEXT) restricting access to group B PMU regs,
+	 * sigill is expected.
+	 */
+	if (have_hwcap2(PPC_FEATURE2_ARCH_3_1))
+		FAIL_IF(catch_sigill(dump_ebb_state));
+	else
+		dump_ebb_state();
+
+	return 0;
+}
+
+int main(void)
+{
+	return test_harness(regs_access_pmccext,"regs_access_pmccext");
+}
-- 
1.8.3.1