x86, reboot: Move the real-mode reboot code to an assembly file
Move the real-mode reboot code out to an assembly file (reboot_32.S)
which is allocated using the common lowmem trampoline allocator.
Signed-off-by: H. Peter Anvin <hpa@linux.intel.com>
LKML-Reference: <4D5DFBE4.7090104@intel.com>
Cc: Stephen Rothwell <sfr@canb.auug.org.au>
Cc: Rafael J. Wysocki <rjw@sisk.pl>
Cc: Matthieu Castet <castet.matthieu@free.fr>
diff --git a/arch/x86/kernel/reboot.c b/arch/x86/kernel/reboot.c
index fc7aae1..10c6619 100644
--- a/arch/x86/kernel/reboot.c
+++ b/arch/x86/kernel/reboot.c
@@ -295,68 +295,16 @@
}
core_initcall(reboot_init);
-/* The following code and data reboots the machine by switching to real
- mode and jumping to the BIOS reset entry point, as if the CPU has
- really been reset. The previous version asked the keyboard
- controller to pulse the CPU reset line, which is more thorough, but
- doesn't work with at least one type of 486 motherboard. It is easy
- to stop this code working; hence the copious comments. */
-static const unsigned long long
-real_mode_gdt_entries [3] =
+extern const unsigned char machine_real_restart_asm[];
+extern const u64 machine_real_restart_gdt[3];
+
+void machine_real_restart(unsigned int type)
{
- 0x0000000000000000ULL, /* Null descriptor */
- 0x00009b000000ffffULL, /* 16-bit real-mode 64k code at 0x00000000 */
- 0x000093000100ffffULL /* 16-bit real-mode 64k data at 0x00000100 */
-};
+ void *restart_va;
+ unsigned long restart_pa;
+ void (*restart_lowmem)(unsigned int);
+ u64 *lowmem_gdt;
-static const struct desc_ptr
-real_mode_gdt = { sizeof (real_mode_gdt_entries) - 1, (long)real_mode_gdt_entries },
-real_mode_idt = { 0x3ff, 0 };
-
-/* This is 16-bit protected mode code to disable paging and the cache,
- switch to real mode and jump to the BIOS reset code.
-
- The instruction that switches to real mode by writing to CR0 must be
- followed immediately by a far jump instruction, which set CS to a
- valid value for real mode, and flushes the prefetch queue to avoid
- running instructions that have already been decoded in protected
- mode.
-
- Clears all the flags except ET, especially PG (paging), PE
- (protected-mode enable) and TS (task switch for coprocessor state
- save). Flushes the TLB after paging has been disabled. Sets CD and
- NW, to disable the cache on a 486, and invalidates the cache. This
- is more like the state of a 486 after reset. I don't know if
- something else should be done for other chips.
-
- More could be done here to set up the registers as if a CPU reset had
- occurred; hopefully real BIOSs don't assume much. */
-static const unsigned char real_mode_switch [] =
-{
- 0x66, 0x0f, 0x20, 0xc0, /* movl %cr0,%eax */
- 0x66, 0x83, 0xe0, 0x11, /* andl $0x00000011,%eax */
- 0x66, 0x0d, 0x00, 0x00, 0x00, 0x60, /* orl $0x60000000,%eax */
- 0x66, 0x0f, 0x22, 0xc0, /* movl %eax,%cr0 */
- 0x66, 0x0f, 0x22, 0xd8, /* movl %eax,%cr3 */
- 0x66, 0x0f, 0x20, 0xc3, /* movl %cr0,%ebx */
- 0x66, 0x81, 0xe3, 0x00, 0x00, 0x00, 0x60, /* andl $0x60000000,%ebx */
- 0x74, 0x02, /* jz f */
- 0x0f, 0x09, /* wbinvd */
- 0x24, 0x10, /* f: andb $0x10,al */
- 0x66, 0x0f, 0x22, 0xc0 /* movl %eax,%cr0 */
-};
-static const unsigned char jump_to_bios [] =
-{
- 0xea, 0x00, 0x00, 0xff, 0xff /* ljmp $0xffff,$0x0000 */
-};
-
-/*
- * Switch to real mode and then execute the code
- * specified by the code and length parameters.
- * We assume that length will aways be less that 100!
- */
-void machine_real_restart(const unsigned char *code, int length)
-{
local_irq_disable();
/* Write zero to CMOS register number 0x0f, which the BIOS POST
@@ -384,41 +332,23 @@
too. */
*((unsigned short *)0x472) = reboot_mode;
- /* For the switch to real mode, copy some code to low memory. It has
- to be in the first 64k because it is running in 16-bit mode, and it
- has to have the same physical and virtual address, because it turns
- off paging. Copy it near the end of the first page, out of the way
- of BIOS variables. */
- memcpy((void *)(0x1000 - sizeof(real_mode_switch) - 100),
- real_mode_switch, sizeof (real_mode_switch));
- memcpy((void *)(0x1000 - 100), code, length);
+ /* Patch the GDT in the low memory trampoline */
+ lowmem_gdt = TRAMPOLINE_SYM(machine_real_restart_gdt);
- /* Set up the IDT for real mode. */
- load_idt(&real_mode_idt);
+ restart_va = TRAMPOLINE_SYM(machine_real_restart_asm);
+ restart_pa = virt_to_phys(restart_va);
+ restart_lowmem = (void (*)(unsigned int))restart_pa;
- /* Set up a GDT from which we can load segment descriptors for real
- mode. The GDT is not used in real mode; it is just needed here to
- prepare the descriptors. */
- load_gdt(&real_mode_gdt);
+ /* GDT[0]: GDT self-pointer */
+ lowmem_gdt[0] =
+ (u64)(sizeof(machine_real_restart_gdt) - 1) +
+ ((u64)virt_to_phys(lowmem_gdt) << 16);
+ /* GDT[1]: 64K real mode code segment */
+ lowmem_gdt[1] =
+ GDT_ENTRY(0x009b, restart_pa, 0xffff);
- /* Load the data segment registers, and thus the descriptors ready for
- real mode. The base address of each segment is 0x100, 16 times the
- selector value being loaded here. This is so that the segment
- registers don't have to be reloaded after switching to real mode:
- the values are consistent for real mode operation already. */
- __asm__ __volatile__ ("movl $0x0010,%%eax\n"
- "\tmovl %%eax,%%ds\n"
- "\tmovl %%eax,%%es\n"
- "\tmovl %%eax,%%fs\n"
- "\tmovl %%eax,%%gs\n"
- "\tmovl %%eax,%%ss" : : : "eax");
-
- /* Jump to the 16-bit code that we copied earlier. It disables paging
- and the cache, switches to real mode, and jumps to the BIOS reset
- entry point. */
- __asm__ __volatile__ ("ljmp $0x0008,%0"
- :
- : "i" ((void *)(0x1000 - sizeof (real_mode_switch) - 100)));
+ /* Jump to the identity-mapped low memory code */
+ restart_lowmem(type);
}
#ifdef CONFIG_APM_MODULE
EXPORT_SYMBOL(machine_real_restart);
@@ -573,7 +503,7 @@
#ifdef CONFIG_X86_32
case BOOT_BIOS:
- machine_real_restart(jump_to_bios, sizeof(jump_to_bios));
+ machine_real_restart(MRR_BIOS);
reboot_type = BOOT_KBD;
break;