linux_kernel/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");
}