x86/itmt: Move the "sched_itmt_enabled" sysctl to debugfs

JIRA: https://issues.redhat.com/browse/RHEL-53784
Conflicts: RHEL is missing upstream 78eb4ea and 83e291d

commit d04013a
Author: K Prateek Nayak <[email protected]>
Date:   Mon Dec 23 04:34:02 2024 +0000

    x86/itmt: Move the "sched_itmt_enabled" sysctl to debugfs

    "sched_itmt_enabled" was only introduced as a debug toggle for any funky
    ITMT behavior. Move the sysctl controlled from
    "/proc/sys/kernel/sched_itmt_enabled" to debugfs at
    "/sys/kernel/debug/x86/sched_itmt_enabled" with a notable change that a
    cat on the file will return "Y" or "N" instead of "1" or "0" to
    indicate that feature is enabled or disabled respectively. Either "0" or
    "N" (or any string that kstrtobool() interprets as false) can be written
    to the file will disable the feature, and writing  either "1" or "Y" (or
    any string that kstrtobool() interprets as true) will enable it back
    when the platform supports ITMT ranking.

    Since ITMT is x86 specific (and PowerPC uses SD_ASYM_PACKING too), the
    toggle was moved to "/sys/kernel/debug/x86/" as opposed to
    "/sys/kernel/debug/sched/"

    Suggested-by: Peter Zijlstra <[email protected]>
    Signed-off-by: K Prateek Nayak <[email protected]>
    Signed-off-by: Peter Zijlstra (Intel) <[email protected]>
    Reviewed-by: Tim Chen <[email protected]>
    Link: https://lore.kernel.org/r/[email protected]

Signed-off-by: David Arcari <[email protected]>

Author: darcari

arch/x86/kernel/itmt.c

@@ -19,6 +19,7 @@
 #include <linux/sched.h>
 #include <linux/cpumask.h>
 #include <linux/cpuset.h>
+#include <linux/debugfs.h>
 #include <linux/mutex.h>
 #include <linux/sysctl.h>
 #include <linux/nodemask.h>
@@ -34,46 +35,38 @@ static bool __read_mostly sched_itmt_capable;
  * of higher turbo frequency for cpus supporting Intel Turbo Boost Max
  * Technology 3.0.
  *
- * It can be set via /proc/sys/kernel/sched_itmt_enabled
+ * It can be set via /sys/kernel/debug/x86/sched_itmt_enabled
  */
 bool __read_mostly sysctl_sched_itmt_enabled;
 
-static int sched_itmt_update_handler(struct ctl_table *table, int write,
-				     void *buffer, size_t *lenp, loff_t *ppos)
+static ssize_t sched_itmt_enabled_write(struct file *filp,
+					const char __user *ubuf,
+					size_t cnt, loff_t *ppos)
 {
-	unsigned int old_sysctl;
-	int ret;
+	ssize_t result;
+	bool orig;
 
 	guard(mutex)(&itmt_update_mutex);
 
-	if (!sched_itmt_capable)
-		return -EINVAL;
-
-	old_sysctl = sysctl_sched_itmt_enabled;
-	ret = proc_dointvec_minmax(table, write, buffer, lenp, ppos);
+	orig = sysctl_sched_itmt_enabled;
+	result = debugfs_write_file_bool(filp, ubuf, cnt, ppos);
 
-	if (!ret && write && old_sysctl != sysctl_sched_itmt_enabled) {
+	if (sysctl_sched_itmt_enabled != orig) {
 		x86_topology_update = true;
 		rebuild_sched_domains();
 	}
 
-	return ret;
+	return result;
 }
 
-static struct ctl_table itmt_kern_table[] = {
-	{
-		.procname	= "sched_itmt_enabled",
-		.data		= &sysctl_sched_itmt_enabled,
-		.maxlen		= sizeof(unsigned int),
-		.mode		= 0644,
-		.proc_handler	= sched_itmt_update_handler,
-		.extra1		= SYSCTL_ZERO,
-		.extra2		= SYSCTL_ONE,
-	},
-	{}
+static const struct file_operations dfs_sched_itmt_fops = {
+	.read =         debugfs_read_file_bool,
+	.write =        sched_itmt_enabled_write,
+	.open =         simple_open,
+	.llseek =       default_llseek,
 };
 
-static struct ctl_table_header *itmt_sysctl_header;
+static struct dentry *dfs_sched_itmt;
 
 /**
  * sched_set_itmt_support() - Indicate platform supports ITMT
@@ -99,9 +92,15 @@ int sched_set_itmt_support(void)
 	if (sched_itmt_capable)
 		return 0;
 
-	itmt_sysctl_header = register_sysctl("kernel", itmt_kern_table);
-	if (!itmt_sysctl_header)
+	dfs_sched_itmt = debugfs_create_file_unsafe("sched_itmt_enabled",
+						    0644,
+						    arch_debugfs_dir,
+						    &sysctl_sched_itmt_enabled,
+						    &dfs_sched_itmt_fops);
+	if (IS_ERR_OR_NULL(dfs_sched_itmt)) {
+		dfs_sched_itmt = NULL;
 		return -ENOMEM;
+	}
 
 	sched_itmt_capable = true;
 
@@ -132,10 +131,8 @@ void sched_clear_itmt_support(void)
 
 	sched_itmt_capable = false;
 
-	if (itmt_sysctl_header) {
-		unregister_sysctl_table(itmt_sysctl_header);
-		itmt_sysctl_header = NULL;
-	}
+	debugfs_remove(dfs_sched_itmt);
+	dfs_sched_itmt = NULL;
 
 	if (sysctl_sched_itmt_enabled) {
 		/* disable sched_itmt if we are no longer ITMT capable */