[PATCH] powerpc/64s/exception: Fix 0x1500 interrupt handler crash

[Nicholas Piggin]

A typo caused the interrupt handler to branch immediately to the common
"unknown interrupt" handler and skip the special case test for denormal
cause.

This does not affect KVM softpatch handling (e.g., for POWER9 TM assist)
because the KVM test was moved to common code by commit 9600f261acaa
("powerpc/64s/exception: Move KVM test to common code") just before this
bug was introduced.

Fixes: 3f7fbd97d07d ("powerpc/64s/exception: Clean up SRR specifiers")
Reported-by: Paul Menzel <pmenzel at molgen.mpg.de>
Tested-by: Paul Menzel <pmenzel at molgen.mpg.de>
Signed-off-by: Nicholas Piggin <npiggin at gmail.com>
---
 arch/powerpc/kernel/exceptions-64s.S          |  2 +-
 tools/testing/selftests/powerpc/math/Makefile |  2 +-
 .../selftests/powerpc/math/fpu_denormal.c     | 38 +++++++++++++++++++
 3 files changed, 40 insertions(+), 2 deletions(-)
 create mode 100644 tools/testing/selftests/powerpc/math/fpu_denormal.c

diff --git a/arch/powerpc/kernel/exceptions-64s.S b/arch/powerpc/kernel/exceptions-64s.S
index fa080694e581..0fc8bad878b2 100644
--- a/arch/powerpc/kernel/exceptions-64s.S
+++ b/arch/powerpc/kernel/exceptions-64s.S
@@ -2551,7 +2551,7 @@ EXC_VIRT_NONE(0x5400, 0x100)
 INT_DEFINE_BEGIN(denorm_exception)
 	IVEC=0x1500
 	IHSRR=1
-	IBRANCH_COMMON=0
+	IBRANCH_TO_COMMON=0
 	IKVM_REAL=1
 INT_DEFINE_END(denorm_exception)
 
diff --git a/tools/testing/selftests/powerpc/math/Makefile b/tools/testing/selftests/powerpc/math/Makefile
index 11a10d7a2bbd..4e2049d2fd8d 100644
--- a/tools/testing/selftests/powerpc/math/Makefile
+++ b/tools/testing/selftests/powerpc/math/Makefile
@@ -1,5 +1,5 @@
 # SPDX-License-Identifier: GPL-2.0
-TEST_GEN_PROGS := fpu_syscall fpu_preempt fpu_signal vmx_syscall vmx_preempt vmx_signal vsx_preempt
+TEST_GEN_PROGS := fpu_syscall fpu_preempt fpu_signal fpu_denormal vmx_syscall vmx_preempt vmx_signal vsx_preempt
 
 top_srcdir = ../../../../..
 include ../../lib.mk
diff --git a/tools/testing/selftests/powerpc/math/fpu_denormal.c b/tools/testing/selftests/powerpc/math/fpu_denormal.c
new file mode 100644
index 000000000000..5f96682abaa8
--- /dev/null
+++ b/tools/testing/selftests/powerpc/math/fpu_denormal.c
@@ -0,0 +1,38 @@
+// SPDX-License-Identifier: GPL-2.0-or-later
+/*
+ * Copyright IBM Corp. 2020
+ *
+ * This test attempts to cause a FP denormal exception on POWER8 CPUs. Unfortunately
+ * if the denormal handler is not configured or working properly, this can cause a bad
+ * crash in kernel mode when the kernel tries to save FP registers when the process
+ * exits.
+ */
+
+#include <stdio.h>
+#include <string.h>
+
+#include "utils.h"
+
+static int test_denormal_fpu(void)
+{
+	unsigned int m32;
+	unsigned long m64;
+	volatile float f;
+	volatile double d;
+
+	/* try to induce lfs <denormal> ; stfd */
+
+	m32 = 0x00715fcf; /* random denormal */
+	memcpy((float *)&f, &m32, sizeof(f));
+	d = f;
+	memcpy(&m64, (double *)&d, sizeof(d));
+
+	FAIL_IF((long)(m64 != 0x380c57f3c0000000)); /* renormalised value */
+
+	return 0;
+}
+
+int main(int argc, char *argv[])
+{
+	return test_harness(test_denormal_fpu, "fpu_denormal");
+}
-- 
2.23.0