Add split lock

splitlock/.gitignore

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+*.o
+sl_test

splitlock/Makefile

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+# SPDX-License-Identifier: GPL-2.0-only
+# Copyright (c) 2022 Intel Corporation.
+
+BIN := sl_test
+
+all: $(BIN)
+
+sl_test: sl_test.c
+	gcc $^ -o $@
+
+clean:
+	rm -rf $(BIN) *.o

splitlock/README.md

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+# SPLIT LOCK
+
+## Description
+A split lock is any atomic operation whose operand crosses two cache lines.
+Since the operand spans two cache lines and the operation must be atomic,
+the system locks the bus while the CPU accesses the two cache lines.
+
+A bus lock is acquired through either split locked access to writeback (WB)
+memory or any locked access to non-WB memory. This is typically thousands of
+cycles slower than an atomic operation within a cache line. It also disrupts
+performance on other cores and brings the whole system to its knees.
+
+## Usage
+make
+./sl_test
+1. Linux kernel driver will export the split_lock_detect flag to /proc/cpuinfo
+   if hardware supports this feature.
+2. Test if the locked instruction will trigger #AC. If no split_lock_detect is
+   not set by default or it is split_lock_detect=warn, #AC will be triggered.
+   The boot parameter could also be set as fatal or ratelimit(ratelimit:1 max
+   ratelimit:1000). If split_lock_detect=fatal, split lock test will output
+   "Caught SIGBUS/#AC" in console.
+   For more, please refer to handle_bus_lock in arch/x86/kernel/cpu/intel.c.
+Examples of exception in dmesg:
+x86/split lock detection: #AC: sl_test/4354 took a split_lock trap at address: 0x401231
+x86/split lock detection: #DB: sl_test/5137 took a bus_lock trap at address: 0x4011f5
+
+## Expected result
+All test results should show pass, no fail.

splitlock/sl_test.c

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+// SPDX-License-Identifier: GPL-2.0-only
+// Copyright (c) 2022 Intel Corporation.
+
+/*
+ * Split lock test app to check if the locked instruction will trigger #AC
+ */
+
+#define _GNU_SOURCE
+#include <sys/types.h>
+#include <sys/stat.h>
+#include <sys/wait.h>
+#include <fcntl.h>
+#include <stdlib.h>
+#include <signal.h>
+#include <stdio.h>
+#include <unistd.h>
+#include <string.h>
+#include <time.h>
+#include <sys/time.h>
+#include <stdio.h>
+
+void catch_sigbus(int sig)
+{
+	printf("Caught SIGBUS/#AC due to split locked access\n");
+
+	exit(-1);
+}
+
+/*
+ * Atomically add 1 to *iptr using "lock addl" instruction.
+ * Since *iptr crosses two cache lines, #AC is generated by the split lock.
+ */
+void do_split_locked_inst(int *iptr)
+{
+	/*
+	 * The distance between iptr and next cache line is 3 bytes.
+	 * Operand size in "addl" is 4 bytes. So iptr will span two cache
+	 * lines. "lock addl" instruction will trigger #AC in hardware
+	 * and kernel either delivers SIGBUS to this process or re-execute
+	 * the instruction depending on
+	 * /sys/kernel/debug/x86/split_lock/user_mode setting.
+	 */
+	asm volatile ("lock addl $1, %0\n\t"
+		      : "=m" (*iptr));
+}
+
+/*
+ * Test SIGBUS delivered after a lock instruction generates #AC for split lock
+ * operand *iptr.
+ */
+void test_sigbus(int *iptr)
+{
+	pid_t pid;
+
+	pid = fork();
+	if (pid)
+		return;
+
+	/*
+	 * The locked instruction will trigger #AC and kernel will deliver
+	 * SIGBUS to this process. The SIGBUS handler in this process will
+	 * verify that the signal is delivered and the process is killed then.
+	 */
+	do_split_locked_inst(iptr);
+}
+
+int main(int argc, char **argv)
+{
+	int *iptr;
+	char *cptr;
+	char *line = NULL;
+	int ret = 0;
+	size_t len;
+	FILE *fp;
+
+	fp = fopen("/proc/cpuinfo", "r");
+	if (!fp)
+		return 1;
+
+	while (getline(&line, &len, fp) != -1) {
+		if (!strncmp(line, "flags", 5)) {
+			if (strstr(line, "split_lock_detect"))
+				ret = 1;
+			break;
+		}
+	}
+
+	free(line);
+	fclose(fp);
+	if (!ret) {
+		printf("split_lock_dect: [FAIL]\n");
+		return !ret;
+	}
+
+	signal(SIGBUS, catch_sigbus);
+
+	/*
+	 * Enable Alignment Checking on x86_64.
+	 * This will generate alignment check on not only split lock but also
+	 * on any misalignment.
+	 * Turn on this for reference only.
+	 */
+	/* __asm__("pushf\norl $0x40000,(%rsp)\npopf"); */
+
+	/* aligned_alloc() provides 64-byte aligned memory */
+	cptr = (char *)aligned_alloc(64, 128);
+
+	/*
+	 * Increment the pointer by 61, making it 3 bytes away from the next
+	 * cache line and 4-byte *iptr across two cache line.
+	 */
+	iptr = (int *)(cptr + 61);
+
+	test_sigbus(iptr);
+
+	free(cptr);
+
+	printf("Split Lock test - exits normally\n");
+
+	return 0;
+}

splitlock/split_lock.sh

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+#!/bin/bash
+# SPDX-License-Identifier: GPL-2.0-only
+# Copyright (c) 2023 Intel Corporation
+# Description:  Test script for split lock of CPU
+
+cd "$(dirname "$0")" 2>/dev/null && source ../.env
+
+: "${CASE_NAME:="check_cpu_info"}"
+
+usage() {
+  cat <<__EOF
+  usage: ./${0##*/} [-t TESTCASE_ID] [-H]
+  -t  TEST CASE ID
+  -H  show this
+__EOF
+}
+
+# Check this feature is enabled/supported
+# Return: 0 for true, otherwise false
+check_cpu_info() {
+  local cpu_func="split_lock_detect"
+  grep -q "$cpu_func" /proc/cpuinfo || block_test "CPU not support:$cpu_func"
+  test_print_trc "/proc/cpuinfo contain '$cpu_func'"
+}
+
+# Call split lock test and check dmesg if #AC is triggered
+split_lock_ac() {
+  local ac_dmesg_start=$(dmesg | grep "x86/split lock detection: #" | wc -l)
+  sl_test
+  local ac_dmesg_end=$(dmesg | grep "x86/split lock detection: #" | wc -l)
+  grep -q "split_lock_detect=fatal" /proc/cmdline && block_test "If set is fatal won't trigger #AC"
+  if [[ $ac_dmesg_end -gt $ac_dmesg_start ]];then
+    test_print_trc "split_lock_dect: [PASS]"
+  else
+    die "split_lock_dect: [FAIL]"
+  fi
+}
+
+split_lock_test() {
+  case $TEST_SCENARIO in
+  sl_on_default)
+    check_cpu_info
+    ;;
+  check_ac_dmesg)
+    split_lock_ac
+    ;;
+  esac
+  return 0
+}
+
+while getopts :t:H arg; do
+  case $arg in
+  t)
+    TEST_SCENARIO=$OPTARG
+    ;;
+  H)
+    usage && exit 0
+    ;;
+  \?)
+    usage
+    die "Invalid Option -$OPTARG"
+    ;;
+  :)
+    usage
+    die "Option -$OPTARG requires an argument."
+    ;;
+  esac
+done
+
+split_lock_test

splitlock/tests

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+# This file collects the split lock feature tests on
+# Intel® Architecture-based platforms.
+
+split_lock.sh -t sl_on_default
+split_lock.sh -t check_ac_dmesg