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Subject[RFC PATCH 10/16] x86/split_lock: Add a debugfs interface to allow user to enable or disable #AC for split lock during run time
Date
User wants to enable or disable #AC for split lock during run time.

The interface /sys/kernel/debug/x86/split_lock/enable is added to allow
user to control #AC for split lock and show current split lock status
during run time.

Writing 1 to the file enables #AC for split lock and writing 0 disables
#AC for split lock.

Reading the file shows current eanbled/disabled status of #AC for split
lock:
0: disabled and 1: enabled.

Signed-off-by: Fenghua Yu <fenghua.yu@intel.com>
---
arch/x86/kernel/cpu/test_ctl.c | 92 ++++++++++++++++++++++++++++++++++++++++++
1 file changed, 92 insertions(+)

diff --git a/arch/x86/kernel/cpu/test_ctl.c b/arch/x86/kernel/cpu/test_ctl.c
index a2f84fcd4da1..e8b3032f3db0 100644
--- a/arch/x86/kernel/cpu/test_ctl.c
+++ b/arch/x86/kernel/cpu/test_ctl.c
@@ -17,6 +17,7 @@
#include <linux/mm.h>
#include <linux/reboot.h>
#include <linux/syscore_ops.h>
+#include <linux/debugfs.h>
#include <asm/msr.h>

#define DISABLE_SPLIT_LOCK_AC 0
@@ -34,6 +35,14 @@ static DEFINE_MUTEX(reexecute_split_lock_mutex);
static int split_lock_ac_kernel = DISABLE_SPLIT_LOCK_AC;
static int split_lock_ac_firmware = DISABLE_SPLIT_LOCK_AC;

+static DEFINE_MUTEX(split_lock_mutex);
+
+struct debugfs_file {
+ char name[32];
+ int mode;
+ const struct file_operations *fops;
+};
+
/* Detete feature of #AC for split lock by probing bit 29 in MSR_TEST_CTL. */
void detect_split_lock_ac(void)
{
@@ -292,6 +301,85 @@ static struct syscore_ops split_lock_syscore_ops = {
.resume = split_lock_bsp_resume,
};

+static int enable_show(void *data, u64 *val)
+{
+ *val = split_lock_ac_kernel;
+
+ return 0;
+}
+
+static int enable_store(void *data, u64 val)
+{
+ u64 msr_val;
+ int cpu;
+
+ if (val != DISABLE_SPLIT_LOCK_AC && val != ENABLE_SPLIT_LOCK_AC)
+ return -EINVAL;
+
+ /* No need to update MSR if new setting is the same as old one. */
+ if (val == split_lock_ac_kernel)
+ return 0;
+
+ mutex_lock(&split_lock_mutex);
+ mutex_lock(&reexecute_split_lock_mutex);
+
+ /*
+ * Wait until it's out of any re-executed split lock instruction
+ * window.
+ */
+ wait_for_reexecution();
+
+ split_lock_ac_kernel = val;
+ /* Read split lock setting on the current CPU. */
+ rdmsrl(MSR_TEST_CTL, msr_val);
+ /* Change the split lock setting. */
+ if (split_lock_ac_kernel == DISABLE_SPLIT_LOCK_AC)
+ msr_val &= ~MSR_TEST_CTL_ENABLE_AC_SPLIT_LOCK;
+ else
+ msr_val |= MSR_TEST_CTL_ENABLE_AC_SPLIT_LOCK;
+ /* Update the split lock setting on all online CPUs. */
+ for_each_online_cpu(cpu)
+ wrmsrl_on_cpu(cpu, MSR_TEST_CTL, msr_val);
+
+ mutex_unlock(&reexecute_split_lock_mutex);
+ mutex_unlock(&split_lock_mutex);
+
+ return 0;
+}
+
+DEFINE_DEBUGFS_ATTRIBUTE(enable_ops, enable_show, enable_store, "%llx\n");
+
+static int __init debugfs_setup_split_lock(void)
+{
+ struct debugfs_file debugfs_files[] = {
+ {"enable", 0600, &enable_ops},
+ };
+ struct dentry *split_lock_dir, *fd;
+ int i;
+
+ split_lock_dir = debugfs_create_dir("split_lock", arch_debugfs_dir);
+ if (!split_lock_dir)
+ goto out;
+
+ /* Create files under split_lock_dir. */
+ for (i = 0; i < ARRAY_SIZE(debugfs_files); i++) {
+ fd = debugfs_create_file(debugfs_files[i].name,
+ debugfs_files[i].mode,
+ split_lock_dir, NULL,
+ debugfs_files[i].fops);
+ if (!fd)
+ goto out_cleanup;
+ }
+
+ return 0;
+
+out_cleanup:
+ debugfs_remove_recursive(split_lock_dir);
+out:
+
+ return -ENOMEM;
+}
+
static int __init split_lock_init(void)
{
int ret;
@@ -299,6 +387,10 @@ static int __init split_lock_init(void)
if (!boot_cpu_has(X86_FEATURE_SPLIT_LOCK_AC))
return -ENODEV;

+ ret = debugfs_setup_split_lock();
+ if (ret)
+ pr_warn("debugfs for #AC for split lock cannot be set up\n");
+
ret = cpuhp_setup_state(CPUHP_AP_ONLINE_DYN, "x86/split_lock:online",
split_lock_online, split_lock_offline);
if (ret < 0)
--
2.5.0
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