x86 idle: remove 32-bit-only "no-hlt" parameter, hlt_works_ok flag

Remove 32-bit x86 a cmdline param "no-hlt",
and the cpuinfo_x86.hlt_works_ok that it sets.

If a user wants to avoid HLT, then "idle=poll"
is much more useful, as it avoids invocation of HLT
in idle, while "no-hlt" failed to do so.

Indeed, hlt_works_ok was consulted in only 3 places.

First, in /proc/cpuinfo where "hlt_bug yes"
would be printed if and only if the user booted
the system with "no-hlt" -- as there was no other code
to set that flag.

Second, check_hlt() would not invoke halt() if "no-hlt"
were on the cmdline.

Third, it was consulted in stop_this_cpu(), which is invoked
by native_machine_halt()/reboot_interrupt()/smp_stop_nmi_callback() --
all cases where the machine is being shutdown/reset.
The flag was not consulted in the more frequently invoked
play_dead()/hlt_play_dead() used in processor offline and suspend.

Since Linux-3.0 there has been a run-time notice upon "no-hlt" invocations
indicating that it would be removed in 2012.

Signed-off-by: Len Brown <len.brown@intel.com>
Cc: x86@kernel.org

Documentation/kernel-parameters.txt

@@ -1881,10 +1881,6 @@ bytes respectively. Such letter suffixes can also be entirely omitted.
 			wfi(ARM) instruction doesn't work correctly and not to
 			use it. This is also useful when using JTAG debugger.
 
-	no-hlt		[BUGS=X86-32] Tells the kernel that the hlt
-			instruction doesn't work correctly and not to
-			use it.
-
 	no_file_caps	Tells the kernel not to honor file capabilities.  The
 			only way then for a file to be executed with privilege
 			is to be setuid root or executed by root.

arch/x86/include/asm/processor.h

@@ -89,7 +89,6 @@ struct cpuinfo_x86 {
 	char			wp_works_ok;	/* It doesn't on 386's */
 
 	/* Problems on some 486Dx4's and old 386's: */
-	char			hlt_works_ok;
 	char			hard_math;
 	char			rfu;
 	char			fdiv_bug;
@@ -165,15 +164,6 @@ DECLARE_PER_CPU_SHARED_ALIGNED(struct cpuinfo_x86, cpu_info);
 
 extern const struct seq_operations cpuinfo_op;
 
-static inline int hlt_works(int cpu)
-{
-#ifdef CONFIG_X86_32
-	return cpu_data(cpu).hlt_works_ok;
-#else
-	return 1;
-#endif
-}
-
 #define cache_line_size()	(boot_cpu_data.x86_cache_alignment)
 
 extern void cpu_detect(struct cpuinfo_x86 *c);

arch/x86/kernel/cpu/bugs.c

@@ -17,15 +17,6 @@
 #include <asm/paravirt.h>
 #include <asm/alternative.h>
 
-static int __init no_halt(char *s)
-{
-	WARN_ONCE(1, "\"no-hlt\" is deprecated, please use \"idle=poll\"\n");
-	boot_cpu_data.hlt_works_ok = 0;
-	return 1;
-}
-
-__setup("no-hlt", no_halt);
-
 static int __init no_387(char *s)
 {
 	boot_cpu_data.hard_math = 0;
@@ -89,23 +80,6 @@ static void __init check_fpu(void)
 		pr_warn("Hmm, FPU with FDIV bug\n");
 }
 
-static void __init check_hlt(void)
-{
-	if (boot_cpu_data.x86 >= 5 || paravirt_enabled())
-		return;
-
-	pr_info("Checking 'hlt' instruction... ");
-	if (!boot_cpu_data.hlt_works_ok) {
-		pr_cont("disabled\n");
-		return;
-	}
-	halt();
-	halt();
-	halt();
-	halt();
-	pr_cont("OK\n");
-}
-
 /*
  * Check whether we are able to run this kernel safely on SMP.
  *
@@ -129,7 +103,6 @@ void __init check_bugs(void)
 	print_cpu_info(&boot_cpu_data);
 #endif
 	check_config();
-	check_hlt();
 	init_utsname()->machine[1] =
 		'0' + (boot_cpu_data.x86 > 6 ? 6 : boot_cpu_data.x86);
 	alternative_instructions();

arch/x86/kernel/cpu/proc.c

@@ -28,15 +28,13 @@ static void show_cpuinfo_misc(struct seq_file *m, struct cpuinfo_x86 *c)
 {
 	seq_printf(m,
 		   "fdiv_bug\t: %s\n"
-		   "hlt_bug\t\t: %s\n"
 		   "f00f_bug\t: %s\n"
 		   "coma_bug\t: %s\n"
 		   "fpu\t\t: %s\n"
 		   "fpu_exception\t: %s\n"
 		   "cpuid level\t: %d\n"
 		   "wp\t\t: %s\n",
 		   c->fdiv_bug ? "yes" : "no",
-		   c->hlt_works_ok ? "no" : "yes",
 		   c->f00f_bug ? "yes" : "no",
 		   c->coma_bug ? "yes" : "no",
 		   c->hard_math ? "yes" : "no",

arch/x86/kernel/process.c

@@ -415,10 +415,8 @@ void stop_this_cpu(void *dummy)
 	set_cpu_online(smp_processor_id(), false);
 	disable_local_APIC();
 
-	for (;;) {
-		if (hlt_works(smp_processor_id()))
-			halt();
-	}
+	for (;;)
+		halt();
 }
 
 /*

arch/x86/xen/setup.c

@@ -556,9 +556,6 @@ void __init xen_arch_setup(void)
 	       COMMAND_LINE_SIZE : MAX_GUEST_CMDLINE);
 
 	/* Set up idle, making sure it calls safe_halt() pvop */
-#ifdef CONFIG_X86_32
-	boot_cpu_data.hlt_works_ok = 1;
-#endif
 	disable_cpuidle();
 	disable_cpufreq();
 	WARN_ON(xen_set_default_idle());