On Sun, May 27, 2018 at 08:45:59AM -0700, Fenghua Yu wrote:
> 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...@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;
> +
No need to test this, just keep moving on. You should never need to
test the result of any debugfs call at all.
> + /* 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;
Same here, no need to test anything.
> + }
> +
> + return 0;
This function can not fail, might as well make it return void :)
thanks,
greg k-h
