x86/fpu: Parse clearcpuid= as early XSAVE argument

With a followon patch we want to make clearcpuid affect the XSAVE
configuration. But xsave is currently initialized before arguments
are parsed. Move the clearcpuid= parsing into the special
early xsave argument parsing code.

Since clearcpuid= contains a = we need to keep the old __setup
around as a dummy, otherwise it would end up as a environment
variable in init's environment.

Signed-off-by: Andi Kleen <ak@linux.intel.com>
Reviewed-by: Thomas Gleixner <tglx@linutronix.de>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Link: http://lkml.kernel.org/r/20171013215645.23166-4-andi@firstfloor.org
Signed-off-by: Ingo Molnar <mingo@kernel.org>

arch/x86/kernel/cpu/common.c

@@ -1301,18 +1301,16 @@ void print_cpu_info(struct cpuinfo_x86 *c)
 		pr_cont(")\n");
 }
 
-static __init int setup_disablecpuid(char *arg)
+/*
+ * clearcpuid= was already parsed in fpu__init_parse_early_param.
+ * But we need to keep a dummy __setup around otherwise it would
+ * show up as an environment variable for init.
+ */
+static __init int setup_clearcpuid(char *arg)
 {
-	int bit;
-
-	if (get_option(&arg, &bit) && bit >= 0 && bit < NCAPINTS * 32)
-		setup_clear_cpu_cap(bit);
-	else
-		return 0;
-
 	return 1;
 }
-__setup("clearcpuid=", setup_disablecpuid);
+__setup("clearcpuid=", setup_clearcpuid);
 
 #ifdef CONFIG_X86_64
 DEFINE_PER_CPU_FIRST(union irq_stack_union,

arch/x86/kernel/fpu/init.c

@@ -249,6 +249,10 @@ static void __init fpu__init_system_ctx_switch(void)
  */
 static void __init fpu__init_parse_early_param(void)
 {
+	char arg[32];
+	char *argptr = arg;
+	int bit;
+
 	if (cmdline_find_option_bool(boot_command_line, "no387"))
 		setup_clear_cpu_cap(X86_FEATURE_FPU);
 
@@ -266,6 +270,13 @@ static void __init fpu__init_parse_early_param(void)
 
 	if (cmdline_find_option_bool(boot_command_line, "noxsaves"))
 		setup_clear_cpu_cap(X86_FEATURE_XSAVES);
+
+	if (cmdline_find_option(boot_command_line, "clearcpuid", arg,
+				sizeof(arg)) &&
+	    get_option(&argptr, &bit) &&
+	    bit >= 0 &&
+	    bit < NCAPINTS * 32)
+		setup_clear_cpu_cap(bit);
 }
 
 /*