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Subject[RFC PATCH 12/16] x86/split_lock: Add a debugfs interface to allow user to change how to handle split lock in kernel mode during run time
Date
CONFIG_SPLIT_LOCK_AC_PANIC_ON_KERNEL defines how to handle split lock in
kernel mode by default. But sometimes user wants to change the default
behavior.

The interface /sys/kernel/debug/x86/split_lock/kernel_mode is added
to allow user to do so.

For example, the interface shows "[re-execute] panic" which
means two behaviors: re-execute kernel faulting instruction
after #AC (default) and panic in #AC.

User can change the default behavior by writing "re-execute" or "panic"
to the interface.

Signed-off-by: Fenghua Yu <fenghua.yu@intel.com>
---
arch/x86/kernel/cpu/test_ctl.c | 89 ++++++++++++++++++++++++++++++++++++++++++
1 file changed, 89 insertions(+)

diff --git a/arch/x86/kernel/cpu/test_ctl.c b/arch/x86/kernel/cpu/test_ctl.c
index 6784f68af26a..0212a7979a14 100644
--- a/arch/x86/kernel/cpu/test_ctl.c
+++ b/arch/x86/kernel/cpu/test_ctl.c
@@ -18,6 +18,7 @@
#include <linux/reboot.h>
#include <linux/syscore_ops.h>
#include <linux/debugfs.h>
+#include <linux/uaccess.h>
#include <asm/msr.h>

#define DISABLE_SPLIT_LOCK_AC 0
@@ -49,6 +50,11 @@ enum {
KERNEL_MODE_LAST
};

+static const char * const kernel_modes[KERNEL_MODE_LAST] = {
+ [KERNEL_MODE_RE_EXECUTE] = "re-execute",
+ [KERNEL_MODE_PANIC] = "panic",
+};
+
static int kernel_mode_reaction = KERNEL_MODE_RE_EXECUTE;

/* Detete feature of #AC for split lock by probing bit 29 in MSR_TEST_CTL. */
@@ -361,10 +367,93 @@ static int enable_store(void *data, u64 val)

DEFINE_DEBUGFS_ATTRIBUTE(enable_ops, enable_show, enable_store, "%llx\n");

+static ssize_t
+mode_show(char __user *user_buf, const char * const *modes, int start_reaction,
+ int last_reaction, int mode_reaction, size_t count, loff_t *ppos)
+{
+ char buf[32], *s = buf;
+ int reaction, len;
+
+ mutex_lock(&split_lock_mutex);
+ for (reaction = start_reaction; reaction < last_reaction; reaction++) {
+ if (reaction == mode_reaction)
+ s += sprintf(s, "[%s] ", modes[reaction]);
+ else
+ s += sprintf(s, "%s ", modes[reaction]);
+ }
+
+ if (s != buf)
+ /* convert the last space to a newline */
+ *(s - 1) = '\n';
+ mutex_unlock(&split_lock_mutex);
+
+ len = strlen(buf);
+
+ return simple_read_from_buffer(user_buf, count, ppos, buf, len);
+}
+
+static ssize_t
+mode_store(const char __user *user_buf, size_t count, const char * const *modes,
+ int start_reaction, int last_reaction, int *mode_reaction)
+{
+ int reaction, len, ret = -EINVAL;
+ const char * const *s, *p;
+ char buf[32];
+
+ len = min(count, sizeof(buf) - 1);
+ if (copy_from_user(buf, user_buf, len))
+ return -EFAULT;
+
+ buf[len] = '\0';
+
+ mutex_lock(&split_lock_mutex);
+ p = memchr(buf, '\n', count);
+ len = p ? p - buf : count;
+
+ reaction = start_reaction;
+ for (s = &modes[reaction]; reaction < last_reaction; s++, reaction++) {
+ if (*s && len == strlen(*s) && !strncmp(buf, *s, len)) {
+ *mode_reaction = reaction;
+ ret = 0;
+ break;
+ }
+ }
+ mutex_unlock(&split_lock_mutex);
+
+ return ret;
+}
+
+static ssize_t kernel_mode_show(struct file *file, char __user *user_buf,
+ size_t count, loff_t *ppos)
+{
+ return mode_show(user_buf, kernel_modes, KERNEL_MODE_RE_EXECUTE,
+ KERNEL_MODE_LAST, kernel_mode_reaction, count, ppos);
+}
+
+static ssize_t kernel_mode_store(struct file *file, const char __user *user_buf,
+ size_t count, loff_t *ppos)
+{
+ int ret;
+
+ ret = mode_store(user_buf, count, kernel_modes, KERNEL_MODE_RE_EXECUTE,
+ KERNEL_MODE_LAST, &kernel_mode_reaction);
+ if (ret)
+ return ret;
+
+ return count;
+}
+
+static const struct file_operations kernel_mode_ops = {
+ .read = kernel_mode_show,
+ .write = kernel_mode_store,
+ .llseek = default_llseek,
+};
+
static int __init debugfs_setup_split_lock(void)
{
struct debugfs_file debugfs_files[] = {
{"enable", 0600, &enable_ops},
+ {"kernel_mode", 0600, &kernel_mode_ops },
};
struct dentry *split_lock_dir, *fd;
int i;
--
2.5.0
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