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x86, reboot: Move the real-mode reboot code to an assembly file

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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>
This commit is contained in:
H. Peter Anvin
2011-02-14 18:36:03 -08:00
parent 014eea518a
commit 3d35ac346e
5 changed files with 160 additions and 105 deletions
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116
arch/x86/kernel/reboot.c
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@@ -295,68 +295,16 @@ static int __init reboot_init(void)
}
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 @@ void machine_real_restart(const unsigned char *code, int length)
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 @@ static void native_machine_emergency_restart(void)
#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;