selftests/powerpc: Test cp_abort during context switch

Test that performing a copy paste sequence in userspace on P9 does not
result in a leak of the copy into the paste of another process.

This is based on Anton Blanchard's context_switch benchmarking code. It
sets up two processes tied to the same CPU, one which copies and one
which pastes.

The paste should never succeed and the test fails if it does.

This is a test for commit, "8a649045 powerpc: Add support for userspace
P9 copy paste."

Patch created with much assistance from Michael Neuling
<mikey@neuling.org>
Signed-off-by: Chris Smart <chris@distroguy.com>
Reviewed-by: Cyril Bur <cyrilbur@gmail.com>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>

tools/testing/selftests/powerpc/Makefile

@@ -14,6 +14,7 @@ export CFLAGS
 
 SUB_DIRS = benchmarks 		\
 	   copyloops		\
+	   context_switch	\
 	   dscr			\
 	   mm			\
 	   pmu			\

tools/testing/selftests/powerpc/context_switch/.gitignore

+cp_abort

tools/testing/selftests/powerpc/context_switch/Makefile

+TEST_PROGS := cp_abort
+
+all: $(TEST_PROGS)
+
+$(TEST_PROGS): ../harness.c ../utils.c
+
+include ../../lib.mk
+
+clean:
+	rm -f $(TEST_PROGS)

tools/testing/selftests/powerpc/context_switch/cp_abort.c

+/*
+ * Adapted from Anton Blanchard's context switch microbenchmark.
+ *
+ * Copyright 2009, Anton Blanchard, IBM Corporation.
+ * Copyright 2016, Mikey Neuling, Chris Smart, IBM Corporation.
+ *
+ * This program is free software; you can redistribute it and/or
+ * modify it under the terms of the GNU General Public License
+ * as published by the Free Software Foundation; either version
+ * 2 of the License, or (at your option) any later version.
+ *
+ * This program tests the copy paste abort functionality of a P9
+ * (or later) by setting up two processes on the same CPU, one
+ * which executes the copy instruction and the other which
+ * executes paste.
+ *
+ * The paste instruction should never succeed, as the cp_abort
+ * instruction is called by the kernel during a context switch.
+ *
+ */
+
+#define _GNU_SOURCE
+
+#include <stdio.h>
+#include <unistd.h>
+#include <stdlib.h>
+#include "utils.h"
+#include <sched.h>
+
+#define READ_FD 0
+#define WRITE_FD 1
+
+#define NUM_LOOPS 1000
+
+/* This defines the "paste" instruction from Power ISA 3.0 Book II, section 4.4. */
+#define PASTE(RA, RB, L, RC) \
+	.long (0x7c00070c | (RA) << (31-15) | (RB) << (31-20) | (L) << (31-10) | (RC) << (31-31))
+
+int paste(void *i)
+{
+	int cr;
+
+	asm volatile(str(PASTE(0, %1, 1, 1))";"
+			"mfcr %0;"
+			: "=r" (cr)
+			: "b" (i)
+			: "memory"
+		    );
+	return cr;
+}
+
+/* This defines the "copy" instruction from Power ISA 3.0 Book II, section 4.4. */
+#define COPY(RA, RB, L) \
+	.long (0x7c00060c | (RA) << (31-15) | (RB) << (31-20) | (L) << (31-10))
+
+void copy(void *i)
+{
+	asm volatile(str(COPY(0, %0, 1))";"
+			:
+			: "b" (i)
+			: "memory"
+		    );
+}
+
+int test_cp_abort(void)
+{
+	/* 128 bytes for a full cache line */
+	char buf[128] __cacheline_aligned;
+	cpu_set_t cpuset;
+	int fd1[2], fd2[2], pid;
+	char c;
+
+	/* only run this test on a P9 or later */
+	SKIP_IF(!have_hwcap2(PPC_FEATURE2_ARCH_3_00));
+
+	/*
+	 * Run both processes on the same CPU, so that copy is more likely
+	 * to leak into a paste.
+	 */
+	CPU_ZERO(&cpuset);
+	CPU_SET(pick_online_cpu(), &cpuset);
+	FAIL_IF(sched_setaffinity(0, sizeof(cpuset), &cpuset));
+
+	FAIL_IF(pipe(fd1) || pipe(fd2));
+
+	pid = fork();
+	FAIL_IF(pid < 0);
+
+	if (!pid) {
+		for (int i = 0; i < NUM_LOOPS; i++) {
+			FAIL_IF((write(fd1[WRITE_FD], &c, 1)) != 1);
+			FAIL_IF((read(fd2[READ_FD], &c, 1)) != 1);
+			/* A paste succeeds if CR0 EQ bit is set */
+			FAIL_IF(paste(buf) & 0x20000000);
+		}
+	} else {
+		for (int i = 0; i < NUM_LOOPS; i++) {
+			FAIL_IF((read(fd1[READ_FD], &c, 1)) != 1);
+			copy(buf);
+			FAIL_IF((write(fd2[WRITE_FD], &c, 1) != 1));
+		}
+	}
+	return 0;
+
+}
+
+int main(int argc, char *argv[])
+{
+	return test_harness(test_cp_abort, "cp_abort");
+}

tools/testing/selftests/powerpc/utils.h

@@ -6,6 +6,8 @@
 #ifndef _SELFTESTS_POWERPC_UTILS_H
 #define _SELFTESTS_POWERPC_UTILS_H
 
+#define __cacheline_aligned __attribute__((aligned(128)))
+
 #include <stdint.h>
 #include <stdbool.h>
 #include <linux/auxvec.h>
@@ -54,4 +56,9 @@ do {								\
 #define _str(s) #s
 #define str(s) _str(s)
 
+/* POWER9 feature */
+#ifndef PPC_FEATURE2_ARCH_3_00
+#define PPC_FEATURE2_ARCH_3_00 0x00800000
+#endif
+
 #endif /* _SELFTESTS_POWERPC_UTILS_H */