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

3 files changed, 27 insertions, 5 deletions

diff --git a/arch/x86/realmode/rm/Makefile b/arch/x86/realmode/rm/Makefile
index 5b84a2d30888..b2d534cab25f 100644
--- a/arch/x86/realmode/rm/Makefile
+++ b/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)
diff --git a/arch/x86/realmode/rm/header.S b/arch/x86/realmode/rm/header.S
index fadf48378ada..a28221d94e69 100644
--- a/arch/x86/realmode/rm/header.S
+++ b/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)
 
diff --git a/arch/x86/realmode/rm/reboot_32.S b/arch/x86/realmode/rm/reboot.S
index 114044876b3d..6bf8feac5557 100644
--- a/arch/x86/realmode/rm/reboot_32.S
+++ b/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