[kvm-unit-tests PATCH v2 8/8] s390x: Add EPSW test

[Nico Boehr <nrb@linux.ibm.com>]

EPSW is only intercepted in certain cases. One of these cases is if we
have a CRW pending and machine check interrupts are masked. This can be
achieved by issuing a RCHP on a valid channel path. This is why we need
the CSS lib and an IO device in this test and hence need to skip it
when not running under QEMU.

Three special cases deserve our attention:

- upper 32 bits of both operands are never modified,
- second operand is not modified if it is zero.
- when both operands are zero, bits 0-11 and 13-31 of the PSW are
  stored in r0.

We also verify we get the correct contents when the second operand is
zero. To do so, we save the data stored at the first operand in the
first case as a reference. As we don't mess with the PSW, the only thing
that might change is the Condition Code (CC) due to some instruction in
between, so we zero it out using zero_out_cc_from_epsw_op1().

This test must be fenced when running in non-QEMU.

Signed-off-by: Nico Boehr <nrb@linux.ibm.com>
Reviewed-by: Claudio Imbrenda <imbrenda@linux.ibm.com>
---
 s390x/Makefile      |   1 +
 s390x/epsw.c        | 113 ++++++++++++++++++++++++++++++++++++++++++++
 s390x/unittests.cfg |   4 ++
 3 files changed, 118 insertions(+)
 create mode 100644 s390x/epsw.c

diff --git a/s390x/Makefile b/s390x/Makefile
index a76b78e5a011..25449708da0d 100644
--- a/s390x/Makefile
+++ b/s390x/Makefile
@@ -27,6 +27,7 @@ tests += $(TEST_DIR)/edat.elf
 tests += $(TEST_DIR)/mvpg-sie.elf
 tests += $(TEST_DIR)/spec_ex-sie.elf
 tests += $(TEST_DIR)/firq.elf
+tests += $(TEST_DIR)/epsw.elf
 
 pv-tests += $(TEST_DIR)/pv-diags.elf
 
diff --git a/s390x/epsw.c b/s390x/epsw.c
new file mode 100644
index 000000000000..192115cf2fac
--- /dev/null
+++ b/s390x/epsw.c
@@ -0,0 +1,113 @@
+/* SPDX-License-Identifier: GPL-2.0-only */
+/*
+ * EPSW Interception Tests
+ *
+ * Copyright IBM Corp. 2022
+ *
+ * Authors:
+ *  Nico Boehr <nrb@linux.ibm.com>
+ */
+#include <libcflat.h>
+#include <css.h>
+#include <vm.h>
+
+static uint32_t zero_out_cc_from_epsw_op1(uint32_t epsw_op1)
+{
+	return epsw_op1 & ~GENMASK(31 - 18, 31 - 20);
+}
+
+static void generate_crw(void)
+{
+	int test_device_sid = css_enumerate();
+	int cc, ret;
+
+	if (!(test_device_sid & SCHID_ONE)) {
+		report_fail("No I/O device found");
+		return;
+	}
+
+	cc = css_enable(test_device_sid, IO_SCH_ISC);
+	report(cc == 0, "Enable subchannel %08x", test_device_sid);
+
+	ret = css_generate_crw(test_device_sid);
+	if (ret)
+		report_fail("Couldn't generate CRW");
+}
+
+static void test_epsw(void)
+{
+	const uint64_t MAGIC1 = 0x1234567890abcdefUL;
+	const uint64_t MAGIC2 = 0xcafedeadbeeffaceUL;
+
+	uint64_t op1 = MAGIC1;
+	uint64_t op2 = MAGIC2;
+	uint32_t prev_epsw_op1;
+
+	/*
+	 * having machine check interrupts masked and pending CRW ensures
+	 * EPSW is intercepted under KVM
+	 */
+	generate_crw();
+
+	report_prefix_push("both operands given");
+	asm volatile(
+		"epsw %0, %1\n"
+		: "+&d" (op1), "+&a" (op2));
+	report(upper_32_bits(op1) == upper_32_bits(MAGIC1) &&
+	       upper_32_bits(op2) == upper_32_bits(MAGIC2),
+	       "upper 32 bits unmodified");
+	report(lower_32_bits(op1) != lower_32_bits(MAGIC1) &&
+	       lower_32_bits(op2) != lower_32_bits(MAGIC2),
+	       "lower 32 bits modified");
+	prev_epsw_op1 = zero_out_cc_from_epsw_op1(lower_32_bits(op1));
+	report_prefix_pop();
+
+	report_prefix_push("second operand 0");
+	op1 = MAGIC1;
+	op2 = MAGIC2;
+	asm volatile(
+		"	lgr 0,%[op2]\n"
+		"	epsw %[op1], 0\n"
+		"	lgr %[op2],0\n"
+		: [op2] "+&d" (op2), [op1] "+&a" (op1)
+		:
+		: "0");
+	report(upper_32_bits(op1) == upper_32_bits(MAGIC1),
+	       "upper 32 bits of first operand unmodified");
+	report(zero_out_cc_from_epsw_op1(lower_32_bits(op1)) == prev_epsw_op1,
+	       "first operand matches previous reading");
+	report(op2 == MAGIC2, "r0 unmodified");
+	report_prefix_pop();
+
+	report_prefix_push("both operands 0");
+	op1 = MAGIC1;
+	asm volatile(
+		"	lgr 0,%[op1]\n"
+		"	epsw 0, 0\n"
+		"	lgr %[op1],0\n"
+		: [op1] "+&d" (op1)
+		:
+		: "0");
+	report(upper_32_bits(op1) == upper_32_bits(MAGIC1),
+	       "upper 32 bits of first operand unmodified");
+	report(zero_out_cc_from_epsw_op1(lower_32_bits(op1)) == prev_epsw_op1,
+	       "first operand matches previous reading");
+	report_prefix_pop();
+}
+
+int main(int argc, char **argv)
+{
+	if (!vm_is_kvm() && !vm_is_tcg()) {
+		report_skip("Not running under QEMU");
+		goto done;
+	}
+
+	report_prefix_push("epsw");
+
+	test_epsw();
+
+done:
+	report_prefix_pop();
+
+	return report_summary();
+}
diff --git a/s390x/unittests.cfg b/s390x/unittests.cfg
index 8b148fe31ac0..aeb82246dddf 100644
--- a/s390x/unittests.cfg
+++ b/s390x/unittests.cfg
@@ -139,3 +139,7 @@ accel = tcg
 
 [sck]
 file = sck.elf
+
+[epsw]
+file = epsw.elf
+extra_params = -device virtio-net-ccw
-- 
2.31.1