x86/cpu: Create helper function to parse the 'clearcpuid=' boot parameter

This is in preparation for a later commit that will reuse this code, to
make review convenient.

Factor out a helper function which does the full handling for this arg
including printing info to the console.

No functional change intended.

Signed-off-by: Brendan Jackman <jackmanb@google.com>
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Link: https://lore.kernel.org/r/20241220-force-cpu-bug-v2-1-7dc71bce742a@google.com

1 files changed, 52 insertions, 44 deletions

diff --git a/arch/x86/kernel/cpu/common.c b/arch/x86/kernel/cpu/common.c
index 76598a93a8fa..137d3e00a5be 100644
--- a/arch/x86/kernel/cpu/common.c
+++ b/arch/x86/kernel/cpu/common.c
@@ -1479,56 +1479,18 @@ static void detect_nopl(void)
 #endif
 }
 
-/*
- * We parse cpu parameters early because fpu__init_system() is executed
- * before parse_early_param().
- */
-static void __init cpu_parse_early_param(void)
+static inline void parse_clearcpuid(char *arg)
 {
-	char arg[128];
-	char *argptr = arg, *opt;
-	int arglen, taint = 0;
-
-#ifdef CONFIG_X86_32
-	if (cmdline_find_option_bool(boot_command_line, "no387"))
-#ifdef CONFIG_MATH_EMULATION
-		setup_clear_cpu_cap(X86_FEATURE_FPU);
-#else
-		pr_err("Option 'no387' required CONFIG_MATH_EMULATION enabled.\n");
-#endif
-
-	if (cmdline_find_option_bool(boot_command_line, "nofxsr"))
-		setup_clear_cpu_cap(X86_FEATURE_FXSR);
-#endif
-
-	if (cmdline_find_option_bool(boot_command_line, "noxsave"))
-		setup_clear_cpu_cap(X86_FEATURE_XSAVE);
-
-	if (cmdline_find_option_bool(boot_command_line, "noxsaveopt"))
-		setup_clear_cpu_cap(X86_FEATURE_XSAVEOPT);
-
-	if (cmdline_find_option_bool(boot_command_line, "noxsaves"))
-		setup_clear_cpu_cap(X86_FEATURE_XSAVES);
-
-	if (cmdline_find_option_bool(boot_command_line, "nousershstk"))
-		setup_clear_cpu_cap(X86_FEATURE_USER_SHSTK);
-
-	/* Minimize the gap between FRED is available and available but disabled. */
-	arglen = cmdline_find_option(boot_command_line, "fred", arg, sizeof(arg));
-	if (arglen != 2 || strncmp(arg, "on", 2))
-		setup_clear_cpu_cap(X86_FEATURE_FRED);
-
-	arglen = cmdline_find_option(boot_command_line, "clearcpuid", arg, sizeof(arg));
-	if (arglen <= 0)
-		return;
+	char *opt;
+	int taint = 0;
 
 	pr_info("Clearing CPUID bits:");
 
-	while (argptr) {
+	while (arg) {
 		bool found __maybe_unused = false;
 		unsigned int bit;
 
-		opt = strsep(&argptr, ",");
+		opt = strsep(&arg, ",");
 
 		/*
 		 * Handle naked numbers first for feature flags which don't
@@ -1570,10 +1532,56 @@ static void __init cpu_parse_early_param(void)
 		if (!found)
 			pr_cont(" (unknown: %s)", opt);
 	}
-	pr_cont("\n");
 
 	if (taint)
 		add_taint(TAINT_CPU_OUT_OF_SPEC, LOCKDEP_STILL_OK);
+
+	pr_cont("\n");
+}
+
+
+/*
+ * We parse cpu parameters early because fpu__init_system() is executed
+ * before parse_early_param().
+ */
+static void __init cpu_parse_early_param(void)
+{
+	char arg[128];
+	int arglen;
+
+#ifdef CONFIG_X86_32
+	if (cmdline_find_option_bool(boot_command_line, "no387"))
+#ifdef CONFIG_MATH_EMULATION
+		setup_clear_cpu_cap(X86_FEATURE_FPU);
+#else
+		pr_err("Option 'no387' required CONFIG_MATH_EMULATION enabled.\n");
+#endif
+
+	if (cmdline_find_option_bool(boot_command_line, "nofxsr"))
+		setup_clear_cpu_cap(X86_FEATURE_FXSR);
+#endif
+
+	if (cmdline_find_option_bool(boot_command_line, "noxsave"))
+		setup_clear_cpu_cap(X86_FEATURE_XSAVE);
+
+	if (cmdline_find_option_bool(boot_command_line, "noxsaveopt"))
+		setup_clear_cpu_cap(X86_FEATURE_XSAVEOPT);
+
+	if (cmdline_find_option_bool(boot_command_line, "noxsaves"))
+		setup_clear_cpu_cap(X86_FEATURE_XSAVES);
+
+	if (cmdline_find_option_bool(boot_command_line, "nousershstk"))
+		setup_clear_cpu_cap(X86_FEATURE_USER_SHSTK);
+
+	/* Minimize the gap between FRED is available and available but disabled. */
+	arglen = cmdline_find_option(boot_command_line, "fred", arg, sizeof(arg));
+	if (arglen != 2 || strncmp(arg, "on", 2))
+		setup_clear_cpu_cap(X86_FEATURE_FRED);
+
+	arglen = cmdline_find_option(boot_command_line, "clearcpuid", arg, sizeof(arg));
+	if (arglen <= 0)
+		return;
+	parse_clearcpuid(arg);
 }
 
 /*