[PATCH] selftests/powerpc: New TM signal self test

[Breno Leitao <leitao@debian.org>]

A new self test that forces MSR[TS] to be set without calling any TM
instruction. This test also tries to cause a page fault at a signal
handler, exactly between MSR[TS] set and tm_recheckpoint(), forcing
thread->texasr to be rewritten with TEXASR[FS] = 0, which will cause a BUG
when tm_recheckpoint() is called.

This test is not deterministic since it is hard to guarantee that the page
access will cause a page fault. Tests have shown that the bug could be
exposed with few interactions in a buggy kernel. This test is configured to
loop 5000x, having a good chance to hit the kernel issue in just one run.
This self test takes less than two seconds to run.

This test uses set/getcontext because the kernel will recheckpoint
zeroed structures, causing the test to segfault, which is undesired because
the test needs to rerun, so, there is a signal handler for SIGSEGV which
will restart the test.

Signed-off-by: Breno Leitao <leitao@debian.org>
---
 tools/testing/selftests/powerpc/tm/.gitignore |   1 +
 tools/testing/selftests/powerpc/tm/Makefile   |   3 +-
 .../powerpc/tm/tm-signal-force-msr.c          | 115 ++++++++++++++++++
 3 files changed, 118 insertions(+), 1 deletion(-)
 create mode 100644 tools/testing/selftests/powerpc/tm/tm-signal-force-msr.c

diff --git a/tools/testing/selftests/powerpc/tm/.gitignore b/tools/testing/selftests/powerpc/tm/.gitignore
index c3ee8393dae8..89679822ebc9 100644
--- a/tools/testing/selftests/powerpc/tm/.gitignore
+++ b/tools/testing/selftests/powerpc/tm/.gitignore
@@ -11,6 +11,7 @@ tm-signal-context-chk-fpu
 tm-signal-context-chk-gpr
 tm-signal-context-chk-vmx
 tm-signal-context-chk-vsx
+tm-signal-force-msr
 tm-vmx-unavail
 tm-unavailable
 tm-trap
diff --git a/tools/testing/selftests/powerpc/tm/Makefile b/tools/testing/selftests/powerpc/tm/Makefile
index 9fc2cf6fbc92..58a2ebd13958 100644
--- a/tools/testing/selftests/powerpc/tm/Makefile
+++ b/tools/testing/selftests/powerpc/tm/Makefile
@@ -4,7 +4,7 @@ SIGNAL_CONTEXT_CHK_TESTS := tm-signal-context-chk-gpr tm-signal-context-chk-fpu
 
 TEST_GEN_PROGS := tm-resched-dscr tm-syscall tm-signal-msr-resv tm-signal-stack \
 	tm-vmxcopy tm-fork tm-tar tm-tmspr tm-vmx-unavail tm-unavailable tm-trap \
-	$(SIGNAL_CONTEXT_CHK_TESTS) tm-sigreturn
+	$(SIGNAL_CONTEXT_CHK_TESTS) tm-sigreturn tm-signal-force-msr
 
 top_srcdir = ../../../../..
 include ../../lib.mk
@@ -20,6 +20,7 @@ $(OUTPUT)/tm-vmx-unavail: CFLAGS += -pthread -m64
 $(OUTPUT)/tm-resched-dscr: ../pmu/lib.c
 $(OUTPUT)/tm-unavailable: CFLAGS += -O0 -pthread -m64 -Wno-error=uninitialized -mvsx
 $(OUTPUT)/tm-trap: CFLAGS += -O0 -pthread -m64
+$(OUTPUT)/tm-signal-force-msr: CFLAGS += -pthread
 
 SIGNAL_CONTEXT_CHK_TESTS := $(patsubst %,$(OUTPUT)/%,$(SIGNAL_CONTEXT_CHK_TESTS))
 $(SIGNAL_CONTEXT_CHK_TESTS): tm-signal.S
diff --git a/tools/testing/selftests/powerpc/tm/tm-signal-force-msr.c b/tools/testing/selftests/powerpc/tm/tm-signal-force-msr.c
new file mode 100644
index 000000000000..4441d61c2328
--- /dev/null
+++ b/tools/testing/selftests/powerpc/tm/tm-signal-force-msr.c
@@ -0,0 +1,115 @@
+// SPDX-License-Identifier: GPL-2.0
+/*
+ * Copyright 2018, Breno Leitao, Gustavo Romero, IBM Corp.
+ */
+
+#define _GNU_SOURCE
+#include <stdio.h>
+#include <stdlib.h>
+#include <signal.h>
+#include <string.h>
+#include <ucontext.h>
+#include <unistd.h>
+
+#include "tm.h"
+#include "utils.h"
+
+#define __MASK(X)       (1UL<<(X))
+#define MSR_TS_S_LG     33                  /* Trans Mem state: Suspended */
+#define MSR_TM          __MASK(MSR_TM_LG)   /* Transactional Mem Available */
+#define MSR_TS_S        __MASK(MSR_TS_S_LG) /* Transaction Suspended */
+
+#define COUNT_MAX       5000                /* Number of interactions */
+
+/* Setting contexts because the test will crash and we want to recover */
+ucontext_t init_context, main_context;
+
+static int count, first_time;
+
+void trap_signal_handler(int signo, siginfo_t *si, void *uc)
+{
+	ucontext_t *ucp = uc;
+
+	/*
+	 * Allocating memory in a signal handler, and never freeing it on
+	 * purpose, forcing the heap increase, so, the memory leak is what
+	 * we want here.
+	 */
+	ucp->uc_link = malloc(sizeof(ucontext_t));
+	memcpy(&ucp->uc_link, &ucp->uc_mcontext, sizeof(ucp->uc_mcontext));
+
+	/* Forcing to enable MSR[TM] */
+	ucp->uc_mcontext.gp_regs[PT_MSR] |= MSR_TS_S;
+
+	/*
+	 * A fork inside a signal handler seems to be more efficient than a
+	 * fork() prior to the signal being raised.
+	 */
+	if (fork() == 0) {
+		/*
+		 * Both child and parent will return, but, child returns
+		 * with count set so it will exit in the next segfault.
+		 * Parent will continue to loop.
+		 */
+		count = COUNT_MAX;
+	}
+
+	/*
+	 * If the change above does not hit the bug, it will cause a
+	 * segmentation fault, since the ck structures are NULL.
+	 */
+}
+
+void seg_signal_handler(int signo, siginfo_t *si, void *uc)
+{
+	if (count == COUNT_MAX) {
+		/* Return to tm_signal_force_msr() and exit */
+		setcontext(&main_context);
+	}
+
+	count++;
+	/* Reexecute the test */
+	setcontext(&init_context);
+}
+
+void tm_trap_test(void)
+{
+	struct sigaction trap_sa, seg_sa;
+
+	trap_sa.sa_flags = SA_SIGINFO;
+	trap_sa.sa_sigaction = trap_signal_handler;
+
+	seg_sa.sa_flags = SA_SIGINFO;
+	seg_sa.sa_sigaction = seg_signal_handler;
+
+	/*
+	 * Set initial context. Will get back here from
+	 * seg_signal_handler()
+	 */
+	getcontext(&init_context);
+
+	/* The signal handler will enable MSR_TS */
+	sigaction(SIGUSR1, &trap_sa, NULL);
+	/* If it does not crash, it will segfault, avoid it to retest */
+	sigaction(SIGSEGV, &seg_sa, NULL);
+
+	raise(SIGUSR1);
+}
+
+int tm_signal_force_msr(void)
+{
+	SKIP_IF(!have_htm());
+
+	/* Will get back here after COUNT_MAX interactions */
+	getcontext(&main_context);
+
+	if (!first_time++)
+		tm_trap_test();
+
+	return EXIT_SUCCESS;
+}
+
+int main(int argc, char **argv)
+{
+	test_harness(tm_signal_force_msr, "tm_signal_force_msr");
+}
-- 
2.19.0