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Subject[tip:x86/trampoline] x86, reboot: Move the real-mode reboot code to an assembly file
Commit-ID:  3d35ac346e981162eeba391e496faceed4753e7b
Gitweb: http://git.kernel.org/tip/3d35ac346e981162eeba391e496faceed4753e7b
Author: H. Peter Anvin <hpa@linux.intel.com>
AuthorDate: Mon, 14 Feb 2011 18:36:03 -0800
Committer: H. Peter Anvin <hpa@linux.intel.com>
CommitDate: Thu, 17 Feb 2011 21:05:34 -0800

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>
---
arch/x86/include/asm/reboot.h | 5 +-
arch/x86/kernel/Makefile | 1 +
arch/x86/kernel/apm_32.c | 12 +----
arch/x86/kernel/reboot.c | 120 ++++++++-----------------------------
arch/x86/kernel/reboot_32.S | 131 +++++++++++++++++++++++++++++++++++++++++
5 files changed, 162 insertions(+), 107 deletions(-)
diff --git a/arch/x86/include/asm/reboot.h b/arch/x86/include/asm/reboot.h
index 562d4fd..3250e3d 100644
--- a/arch/x86/include/asm/reboot.h
+++ b/arch/x86/include/asm/reboot.h
@@ -18,7 +18,10 @@ extern struct machine_ops machine_ops;

void native_machine_crash_shutdown(struct pt_regs *regs);
void native_machine_shutdown(void);
-void machine_real_restart(const unsigned char *code, int length);
+void machine_real_restart(unsigned int type);
+/* These must match dispatch_table in reboot_32.S */
+#define MRR_BIOS 0
+#define MRR_APM 1

typedef void (*nmi_shootdown_cb)(int, struct die_args*);
void nmi_shootdown_cpus(nmi_shootdown_cb callback);
diff --git a/arch/x86/kernel/Makefile b/arch/x86/kernel/Makefile
index 2e8ce0d..778c5b93 100644
--- a/arch/x86/kernel/Makefile
+++ b/arch/x86/kernel/Makefile
@@ -59,6 +59,7 @@ obj-$(CONFIG_STACKTRACE) += stacktrace.o
obj-y += cpu/
obj-y += acpi/
obj-y += reboot.o
+obj-$(CONFIG_X86_32) += reboot_32.o
obj-$(CONFIG_MCA) += mca_32.o
obj-$(CONFIG_X86_MSR) += msr.o
obj-$(CONFIG_X86_CPUID) += cpuid.o
diff --git a/arch/x86/kernel/apm_32.c b/arch/x86/kernel/apm_32.c
index 0e4f24c..b929108 100644
--- a/arch/x86/kernel/apm_32.c
+++ b/arch/x86/kernel/apm_32.c
@@ -975,20 +975,10 @@ recalc:

static void apm_power_off(void)
{
- unsigned char po_bios_call[] = {
- 0xb8, 0x00, 0x10, /* movw $0x1000,ax */
- 0x8e, 0xd0, /* movw ax,ss */
- 0xbc, 0x00, 0xf0, /* movw $0xf000,sp */
- 0xb8, 0x07, 0x53, /* movw $0x5307,ax */
- 0xbb, 0x01, 0x00, /* movw $0x0001,bx */
- 0xb9, 0x03, 0x00, /* movw $0x0003,cx */
- 0xcd, 0x15 /* int $0x15 */
- };
-
/* Some bioses don't like being called from CPU != 0 */
if (apm_info.realmode_power_off) {
set_cpus_allowed_ptr(current, cpumask_of(0));
- machine_real_restart(po_bios_call, sizeof(po_bios_call));
+ machine_real_restart(MRR_APM);
} else {
(void)set_system_power_state(APM_STATE_OFF);
}
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 @@ 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] =
-{
- 0x0000000000000000ULL, /* Null descriptor */
- 0x00009b000000ffffULL, /* 16-bit real-mode 64k code at 0x00000000 */
- 0x000093000100ffffULL /* 16-bit real-mode 64k data at 0x00000100 */
-};
+extern const unsigned char machine_real_restart_asm[];
+extern const u64 machine_real_restart_gdt[3];

-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 [] =
+void machine_real_restart(unsigned int type)
{
- 0xea, 0x00, 0x00, 0xff, 0xff /* ljmp $0xffff,$0x0000 */
-};
+ void *restart_va;
+ unsigned long restart_pa;
+ void (*restart_lowmem)(unsigned int);
+ u64 *lowmem_gdt;

-/*
- * 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);
-
- /* Set up the IDT for real mode. */
- load_idt(&real_mode_idt);
-
- /* 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);
-
- /* 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)));
+ /* Patch the GDT in the low memory trampoline */
+ lowmem_gdt = TRAMPOLINE_SYM(machine_real_restart_gdt);
+
+ restart_va = TRAMPOLINE_SYM(machine_real_restart_asm);
+ restart_pa = virt_to_phys(restart_va);
+ restart_lowmem = (void (*)(unsigned int))restart_pa;
+
+ /* 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);
+
+ /* 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;
diff --git a/arch/x86/kernel/reboot_32.S b/arch/x86/kernel/reboot_32.S
new file mode 100644
index 0000000..f242356
--- /dev/null
+++ b/arch/x86/kernel/reboot_32.S
@@ -0,0 +1,131 @@
+#include <linux/linkage.h>
+#include <linux/init.h>
+#include <asm/segment.h>
+#include <asm/page_types.h>
+
+/*
+ * 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.
+ *
+ * This code is called with the restart type (0 = BIOS, 1 = APM) in %eax.
+ */
+ .section ".x86_trampoline","a"
+ .balign 16
+ .code32
+ENTRY(machine_real_restart_asm)
+r_base = .
+ /* Get our own relocated address */
+ call 1f
+1: popl %ebx
+ subl $1b, %ebx
+
+ /* Patch post-real-mode segment jump */
+ movw dispatch_table(%ebx,%ecx,2),%cx
+ movw %cx, 101f(%ebx)
+ movw %ax, 102f(%ebx)
+
+ /* Set up the IDT for real mode. */
+ lidtl machine_real_restart_idt(%ebx)
+
+ /*
+ * 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.
+ */
+ lgdtl machine_real_restart_gdt(%ebx)
+
+ /*
+ * Load the data segment registers with 16-bit compatible values
+ */
+ movl $16, %ecx
+ movl %ecx, %ds
+ movl %ecx, %es
+ movl %ecx, %fs
+ movl %ecx, %gs
+ movl %ecx, %ss
+ ljmpl $8, $1f - r_base
+
+/*
+ * 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. This is not the
+ * actual BIOS entry point, anyway (that is at 0xfffffff0).
+ *
+ * Most of this work is probably excessive, but it is what is tested.
+ */
+ .code16
+1:
+ xorl %ecx, %ecx
+ movl %cr0, %eax
+ andl $0x00000011, %eax
+ orl $0x60000000, %eax
+ movl %eax, %cr0
+ movl %ecx, %cr3
+ movl %cr0, %edx
+ andl $0x60000000, %edx /* If no cache bits -> no wbinvd */
+ jz 2f
+ wbinvd
+2:
+ andb $0x10, %al
+ movl %eax, %cr0
+ .byte 0xea /* ljmpw */
+101: .word 0 /* Offset */
+102: .word 0 /* Segment */
+
+bios:
+ ljmpw $0xf000, $0xfff0
+
+apm:
+ movw $0x1000, %ax
+ movw %ax, %ss
+ movw $0xf000, %sp
+ movw $0x5307, %ax
+ movw $0x0001, %bx
+ movw $0x0003, %cx
+ int $0x15
+
+END(machine_real_restart_asm)
+
+ .balign 16
+ /* These must match <asm/reboot.h */
+dispatch_table:
+ .word bios - r_base
+ .word apm - r_base
+END(dispatch_table)
+
+ .balign 16
+machine_real_restart_idt:
+ .word 0xffff /* Length - real mode default value */
+ .long 0 /* Base - real mode default value */
+END(machine_real_restart_idt)
+
+ .balign 16
+ENTRY(machine_real_restart_gdt)
+ .quad 0 /* Self-pointer, filled in by PM code */
+ .quad 0 /* 16-bit code segment, filled in by PM code */
+ /*
+ * 16-bit data segment with the selector value 16 = 0x10 and
+ * base value 0x100; since this is consistent with real mode
+ * semantics we don't have to reload the segments once CR0.PE = 0.
+ */
+ .quad GDT_ENTRY(0x0093, 0x100, 0xffff)
+END(machine_real_restart_gdt)

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