x86-64, reboot: Allow reboot=bios and reboot-cpu override on x86-64

With the revamped realmode trampoline code, it is trivial to extend
support for reboot=bios to x86-64.  Furthermore, while we are at it,
remove the restriction that only we can only override the reboot CPU
on 32 bits.

Signed-off-by: H. Peter Anvin <hpa@zytor.com>
Link: http://lkml.kernel.org/n/tip-jopx7y6g6dbcx4tpal8q0jlr@git.kernel.org

arch/x86/include/asm/emergency-restart.h

@@ -4,9 +4,7 @@
 enum reboot_type {
 	BOOT_TRIPLE = 't',
 	BOOT_KBD = 'k',
-#ifdef CONFIG_X86_32
 	BOOT_BIOS = 'b',
-#endif
 	BOOT_ACPI = 'a',
 	BOOT_EFI = 'e',
 	BOOT_CF9 = 'p',

arch/x86/include/asm/realmode.h

@@ -21,8 +21,9 @@ struct real_mode_header {
 	u32	wakeup_header;
 #endif
 	/* APM/BIOS reboot */
-#ifdef CONFIG_X86_32
 	u32	machine_real_restart_asm;
+#ifdef CONFIG_X86_64
+	u32	machine_real_restart_seg;
 #endif
 };
 

arch/x86/include/asm/reboot.h

@@ -18,8 +18,8 @@ extern struct machine_ops machine_ops;
 
 void native_machine_crash_shutdown(struct pt_regs *regs);
 void native_machine_shutdown(void);
-void machine_real_restart(unsigned int type);
-/* These must match dispatch_table in reboot_32.S */
+void __noreturn machine_real_restart(unsigned int type);
+/* These must match dispatch in arch/x86/realmore/rm/reboot.S */
 #define MRR_BIOS	0
 #define MRR_APM		1
 

arch/x86/kernel/reboot.c

@@ -20,14 +20,12 @@
 #include <asm/virtext.h>
 #include <asm/cpu.h>
 #include <asm/nmi.h>
+#include <asm/smp.h>
 
-#ifdef CONFIG_X86_32
-# include <linux/ctype.h>
-# include <linux/mc146818rtc.h>
-# include <asm/realmode.h>
-#else
-# include <asm/x86_init.h>
-#endif
+#include <linux/ctype.h>
+#include <linux/mc146818rtc.h>
+#include <asm/realmode.h>
+#include <asm/x86_init.h>
 
 /*
  * Power off function, if any
@@ -49,7 +47,7 @@ int reboot_force;
  */
 static int reboot_default = 1;
 
-#if defined(CONFIG_X86_32) && defined(CONFIG_SMP)
+#ifdef CONFIG_SMP
 static int reboot_cpu = -1;
 #endif
 
@@ -67,8 +65,8 @@ bool port_cf9_safe = false;
  * reboot=b[ios] | s[mp] | t[riple] | k[bd] | e[fi] [, [w]arm | [c]old] | p[ci]
  * warm   Don't set the cold reboot flag
  * cold   Set the cold reboot flag
- * bios   Reboot by jumping through the BIOS (only for X86_32)
- * smp    Reboot by executing reset on BSP or other CPU (only for X86_32)
+ * bios   Reboot by jumping through the BIOS
+ * smp    Reboot by executing reset on BSP or other CPU
  * triple Force a triple fault (init)
  * kbd    Use the keyboard controller. cold reset (default)
  * acpi   Use the RESET_REG in the FADT
@@ -95,7 +93,6 @@ static int __init reboot_setup(char *str)
 			reboot_mode = 0;
 			break;
 
-#ifdef CONFIG_X86_32
 #ifdef CONFIG_SMP
 		case 's':
 			if (isdigit(*(str+1))) {
@@ -112,7 +109,6 @@ static int __init reboot_setup(char *str)
 #endif /* CONFIG_SMP */
 
 		case 'b':
-#endif
 		case 'a':
 		case 'k':
 		case 't':
@@ -138,7 +134,6 @@ static int __init reboot_setup(char *str)
 __setup("reboot=", reboot_setup);
 
 
-#ifdef CONFIG_X86_32
 /*
  * Reboot options and system auto-detection code provided by
  * Dell Inc. so their systems "just work". :-)
@@ -157,11 +152,8 @@ static int __init set_bios_reboot(const struct dmi_system_id *d)
 	return 0;
 }
 
-void machine_real_restart(unsigned int type)
+void __noreturn machine_real_restart(unsigned int type)
 {
-	void (*restart_lowmem)(unsigned int) = (void (*)(unsigned int))
-		real_mode_header->machine_real_restart_asm;
-
 	local_irq_disable();
 
 	/*
@@ -181,7 +173,11 @@ void machine_real_restart(unsigned int type)
 	/*
 	 * Switch back to the initial page table.
 	 */
+#ifdef CONFIG_X86_32
 	load_cr3(initial_page_table);
+#else
+	write_cr3(real_mode_header->trampoline_pgd);
+#endif
 
 	/*
 	 * Write 0x1234 to absolute memory location 0x472.  The BIOS reads
@@ -192,14 +188,21 @@ void machine_real_restart(unsigned int type)
 	*((unsigned short *)0x472) = reboot_mode;
 
 	/* Jump to the identity-mapped low memory code */
-	restart_lowmem(type);
+#ifdef CONFIG_X86_32
+	asm volatile("jmpl *%0" : :
+		     "rm" (real_mode_header->machine_real_restart_asm),
+		     "a" (type));
+#else
+	asm volatile("ljmpl *%0" : :
+		     "m" (real_mode_header->machine_real_restart_asm),
+		     "D" (type));
+#endif
+	unreachable();
 }
 #ifdef CONFIG_APM_MODULE
 EXPORT_SYMBOL(machine_real_restart);
 #endif
 
-#endif /* CONFIG_X86_32 */
-
 /*
  * Some Apple MacBook and MacBookPro's needs reboot=p to be able to reboot
  */
@@ -223,11 +226,9 @@ static int __init set_kbd_reboot(const struct dmi_system_id *d)
 }
 
 /*
- * This is a single dmi_table handling all reboot quirks.  Note that
- * REBOOT_BIOS is only available for 32bit
+ * This is a single dmi_table handling all reboot quirks.
  */
 static struct dmi_system_id __initdata reboot_dmi_table[] = {
-#ifdef CONFIG_X86_32
 	{	/* Handle problems with rebooting on Dell E520's */
 		.callback = set_bios_reboot,
 		.ident = "Dell E520",
@@ -377,7 +378,6 @@ static struct dmi_system_id __initdata reboot_dmi_table[] = {
 			DMI_MATCH(DMI_BOARD_NAME, "P4S800"),
 		},
 	},
-#endif /* CONFIG_X86_32 */
 
 	{	/* Handle reboot issue on Acer Aspire one */
 		.callback = set_kbd_reboot,
@@ -576,13 +576,11 @@ static void native_machine_emergency_restart(void)
 			reboot_type = BOOT_KBD;
 			break;
 
-#ifdef CONFIG_X86_32
 		case BOOT_BIOS:
 			machine_real_restart(MRR_BIOS);
 
 			reboot_type = BOOT_KBD;
 			break;
-#endif
 
 		case BOOT_ACPI:
 			acpi_reboot();
@@ -624,12 +622,10 @@ void native_machine_shutdown(void)
 	/* The boot cpu is always logical cpu 0 */
 	int reboot_cpu_id = 0;
 
-#ifdef CONFIG_X86_32
 	/* See if there has been given a command line override */
 	if ((reboot_cpu != -1) && (reboot_cpu < nr_cpu_ids) &&
 		cpu_online(reboot_cpu))
 		reboot_cpu_id = reboot_cpu;
-#endif
 
 	/* Make certain the cpu I'm about to reboot on is online */
 	if (!cpu_online(reboot_cpu_id))

arch/x86/realmode/rm/Makefile

@@ -22,7 +22,7 @@ wakeup-objs	+= video-bios.o
 realmode-y			+= header.o
 realmode-y			+= trampoline_$(BITS).o
 realmode-y			+= stack.o
-realmode-$(CONFIG_X86_32)	+= reboot_32.o
+realmode-y			+= reboot.o
 realmode-$(CONFIG_ACPI_SLEEP)	+= $(wakeup-objs)
 
 targets	+= $(realmode-y)

arch/x86/realmode/rm/header.S

@@ -6,6 +6,7 @@
 
 #include <linux/linkage.h>
 #include <asm/page_types.h>
+#include <asm/segment.h>
 
 #include "realmode.h"
 
@@ -28,8 +29,9 @@ GLOBAL(real_mode_header)
 	.long	pa_wakeup_header
 #endif
 	/* APM/BIOS reboot */
-#ifdef CONFIG_X86_32
 	.long	pa_machine_real_restart_asm
+#ifdef CONFIG_X86_64
+	.long	__KERNEL32_CS
 #endif
 END(real_mode_header)
 

arch/x86/realmode/rm/reboot_32.S → arch/x86/realmode/rm/reboot.S

@@ -2,6 +2,8 @@
 #include <linux/init.h>
 #include <asm/segment.h>
 #include <asm/page_types.h>
+#include <asm/processor-flags.h>
+#include <asm/msr-index.h>
 #include "realmode.h"
 
 /*
@@ -12,13 +14,31 @@
  * doesn't work with at least one type of 486 motherboard.  It is easy
  * to stop this code working; hence the copious comments.
  *
- * This code is called with the restart type (0 = BIOS, 1 = APM) in %eax.
+ * This code is called with the restart type (0 = BIOS, 1 = APM) in
+ * the primary argument register (%eax for 32 bit, %edi for 64 bit).
  */
 	.section ".text32", "ax"
 	.code32
-
-	.balign	16
 ENTRY(machine_real_restart_asm)
+
+#ifdef CONFIG_X86_64
+
+	/* Disable paging to drop us out of long mode */
+	movl	%cr0, %eax
+	andl	$~X86_CR0_PG, %eax
+	movl	%eax, %cr0
+	jmp	1f	/* "A branch" may be needed here, assume near is OK */
+
+1:
+	xorl	%eax, %eax
+	xorl	%edx, %edx
+	movl	$MSR_EFER, %ecx
+	wrmsr
+
+	movl	%edi, %eax
+
+#endif /* CONFIG_X86_64 */
+
 	/* Set up the IDT for real mode. */
 	lidtl	pa_machine_real_restart_idt