x86/tsx: Get the tsx= command line parameter with early_param()

Use early_param() to get the value of the tsx= command line parameter. It is
an early parameter, because it must be parsed before tsx_init(), which is
called long before kernel_init(), where normal parameters are parsed.

Although cmdline_find_option() from tsx_init() works fine, the option is later
reported as unknown and passed to user space. The latter is not a real issue,
but the former is confusing and makes people wonder if the tsx= parameter had
any effect and double-check for typos unnecessarily.

The behavior changes slightly if "tsx" is given without any argument (which is
invalid syntax). Until now, the kernel logged an error message and disabled
TSX. Now, the kernel still issues a warning (Malformed early option 'tsx'),
but TSX state is unchanged. The new behavior is consistent with other
parameters, e.g. "tsx_async_abort".

   [ bp: Fixup minor formatting request during review. ]

Suggested-by: Pawan Gupta <pawan.kumar.gupta@linux.intel.com>
Signed-off-by: Petr Tesarik <ptesarik@suse.com>
Signed-off-by: Borislav Petkov (AMD) <bp@alien8.de>
Link: https://lore.kernel.org/all/cover.1758906115.git.ptesarik@suse.com

Author: ptesarik

arch/x86/kernel/cpu/tsx.c

@@ -20,13 +20,16 @@
 #define pr_fmt(fmt) "tsx: " fmt
 
 enum tsx_ctrl_states {
+	TSX_CTRL_AUTO,
 	TSX_CTRL_ENABLE,
 	TSX_CTRL_DISABLE,
 	TSX_CTRL_RTM_ALWAYS_ABORT,
 	TSX_CTRL_NOT_SUPPORTED,
 };
 
-static enum tsx_ctrl_states tsx_ctrl_state __ro_after_init = TSX_CTRL_NOT_SUPPORTED;
+static enum tsx_ctrl_states tsx_ctrl_state __ro_after_init =
+	IS_ENABLED(CONFIG_X86_INTEL_TSX_MODE_AUTO) ? TSX_CTRL_AUTO   :
+	IS_ENABLED(CONFIG_X86_INTEL_TSX_MODE_OFF) ? TSX_CTRL_DISABLE : TSX_CTRL_ENABLE;
 
 static void tsx_disable(void)
 {
@@ -163,11 +166,28 @@ static void tsx_dev_mode_disable(void)
 	}
 }
 
-void __init tsx_init(void)
+static int __init tsx_parse_cmdline(char *str)
 {
-	char arg[5] = {};
-	int ret;
+	if (!str)
+		return -EINVAL;
+
+	if (!strcmp(str, "on")) {
+		tsx_ctrl_state = TSX_CTRL_ENABLE;
+	} else if (!strcmp(str, "off")) {
+		tsx_ctrl_state = TSX_CTRL_DISABLE;
+	} else if (!strcmp(str, "auto")) {
+		tsx_ctrl_state = TSX_CTRL_AUTO;
+	} else {
+		tsx_ctrl_state = TSX_CTRL_DISABLE;
+		pr_err("invalid option, defaulting to off\n");
+	}
+
+	return 0;
+}
+early_param("tsx", tsx_parse_cmdline);
 
+void __init tsx_init(void)
+{
 	tsx_dev_mode_disable();
 
 	/*
@@ -201,27 +221,8 @@ void __init tsx_init(void)
 		return;
 	}
 
-	ret = cmdline_find_option(boot_command_line, "tsx", arg, sizeof(arg));
-	if (ret >= 0) {
-		if (!strcmp(arg, "on")) {
-			tsx_ctrl_state = TSX_CTRL_ENABLE;
-		} else if (!strcmp(arg, "off")) {
-			tsx_ctrl_state = TSX_CTRL_DISABLE;
-		} else if (!strcmp(arg, "auto")) {
-			tsx_ctrl_state = x86_get_tsx_auto_mode();
-		} else {
-			tsx_ctrl_state = TSX_CTRL_DISABLE;
-			pr_err("invalid option, defaulting to off\n");
-		}
-	} else {
-		/* tsx= not provided */
-		if (IS_ENABLED(CONFIG_X86_INTEL_TSX_MODE_AUTO))
-			tsx_ctrl_state = x86_get_tsx_auto_mode();
-		else if (IS_ENABLED(CONFIG_X86_INTEL_TSX_MODE_OFF))
-			tsx_ctrl_state = TSX_CTRL_DISABLE;
-		else
-			tsx_ctrl_state = TSX_CTRL_ENABLE;
-	}
+	if (tsx_ctrl_state == TSX_CTRL_AUTO)
+		tsx_ctrl_state = x86_get_tsx_auto_mode();
 
 	if (tsx_ctrl_state == TSX_CTRL_DISABLE) {
 		tsx_disable();