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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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