1 /* -*- linux-c -*- ------------------------------------------------------- * 2 * 3 * Copyright (C) 1991, 1992 Linus Torvalds 4 * Copyright 2007 rPath, Inc. - All Rights Reserved 5 * 6 * This file is part of the Linux kernel, and is made available under 7 * the terms of the GNU General Public License version 2. 8 * 9 * ----------------------------------------------------------------------- */ 10 11 /* 12 * Prepare the machine for transition to protected mode. 13 */ 14 15 #include "boot.h" 16 #include <asm/segment.h> 17 18 /* 19 * Invoke the realmode switch hook if present; otherwise 20 * disable all interrupts. 21 */ 22 static void realmode_switch_hook(void) 23 { 24 if (boot_params.hdr.realmode_swtch) { 25 asm volatile("lcallw *%0" 26 : : "m" (boot_params.hdr.realmode_swtch) 27 : "eax", "ebx", "ecx", "edx"); 28 } else { 29 asm volatile("cli"); 30 outb(0x80, 0x70); /* Disable NMI */ 31 io_delay(); 32 } 33 } 34 35 /* 36 * A zImage kernel is loaded at 0x10000 but wants to run at 0x1000. 37 * A bzImage kernel is loaded and runs at 0x100000. 38 */ 39 static void move_kernel_around(void) 40 { 41 /* Note: rely on the compile-time option here rather than 42 the LOADED_HIGH flag. The Qemu kernel loader unconditionally 43 sets the loadflags to zero. */ 44 #ifndef __BIG_KERNEL__ 45 u16 dst_seg, src_seg; 46 u32 syssize; 47 48 dst_seg = 0x1000 >> 4; 49 src_seg = 0x10000 >> 4; 50 syssize = boot_params.hdr.syssize; /* Size in 16-byte paragraphs */ 51 52 while (syssize) { 53 int paras = (syssize >= 0x1000) ? 0x1000 : syssize; 54 int dwords = paras << 2; 55 56 asm volatile("pushw %%es ; " 57 "pushw %%ds ; " 58 "movw %1,%%es ; " 59 "movw %2,%%ds ; " 60 "xorw %%di,%%di ; " 61 "xorw %%si,%%si ; " 62 "rep;movsl ; " 63 "popw %%ds ; " 64 "popw %%es" 65 : "+c" (dwords) 66 : "r" (dst_seg), "r" (src_seg) 67 : "esi", "edi"); 68 69 syssize -= paras; 70 dst_seg += paras; 71 src_seg += paras; 72 } 73 #endif 74 } 75 76 /* 77 * Disable all interrupts at the legacy PIC. 78 */ 79 static void mask_all_interrupts(void) 80 { 81 outb(0xff, 0xa1); /* Mask all interrupts on the secondary PIC */ 82 io_delay(); 83 outb(0xfb, 0x21); /* Mask all but cascade on the primary PIC */ 84 io_delay(); 85 } 86 87 /* 88 * Reset IGNNE# if asserted in the FPU. 89 */ 90 static void reset_coprocessor(void) 91 { 92 outb(0, 0xf0); 93 io_delay(); 94 outb(0, 0xf1); 95 io_delay(); 96 } 97 98 /* 99 * Set up the GDT 100 */ 101 102 struct gdt_ptr { 103 u16 len; 104 u32 ptr; 105 } __attribute__((packed)); 106 107 static void setup_gdt(void) 108 { 109 /* There are machines which are known to not boot with the GDT 110 being 8-byte unaligned. Intel recommends 16 byte alignment. */ 111 static const u64 boot_gdt[] __attribute__((aligned(16))) = { 112 /* CS: code, read/execute, 4 GB, base 0 */ 113 [GDT_ENTRY_BOOT_CS] = GDT_ENTRY(0xc09b, 0, 0xfffff), 114 /* DS: data, read/write, 4 GB, base 0 */ 115 [GDT_ENTRY_BOOT_DS] = GDT_ENTRY(0xc093, 0, 0xfffff), 116 /* TSS: 32-bit tss, 104 bytes, base 4096 */ 117 /* We only have a TSS here to keep Intel VT happy; 118 we don't actually use it for anything. */ 119 [GDT_ENTRY_BOOT_TSS] = GDT_ENTRY(0x0089, 4096, 103), 120 }; 121 /* Xen HVM incorrectly stores a pointer to the gdt_ptr, instead 122 of the gdt_ptr contents. Thus, make it static so it will 123 stay in memory, at least long enough that we switch to the 124 proper kernel GDT. */ 125 static struct gdt_ptr gdt; 126 127 gdt.len = sizeof(boot_gdt)-1; 128 gdt.ptr = (u32)&boot_gdt + (ds() << 4); 129 130 asm volatile("lgdtl %0" : : "m" (gdt)); 131 } 132 133 /* 134 * Set up the IDT 135 */ 136 static void setup_idt(void) 137 { 138 static const struct gdt_ptr null_idt = {0, 0}; 139 asm volatile("lidtl %0" : : "m" (null_idt)); 140 } 141 142 /* 143 * Actual invocation sequence 144 */ 145 void go_to_protected_mode(void) 146 { 147 /* Hook before leaving real mode, also disables interrupts */ 148 realmode_switch_hook(); 149 150 /* Move the kernel/setup to their final resting places */ 151 move_kernel_around(); 152 153 /* Enable the A20 gate */ 154 if (enable_a20()) { 155 puts("A20 gate not responding, unable to boot...\n"); 156 die(); 157 } 158 159 /* Reset coprocessor (IGNNE#) */ 160 reset_coprocessor(); 161 162 /* Mask all interrupts in the PIC */ 163 mask_all_interrupts(); 164 165 /* Actual transition to protected mode... */ 166 setup_idt(); 167 setup_gdt(); 168 protected_mode_jump(boot_params.hdr.code32_start, 169 (u32)&boot_params + (ds() << 4)); 170 } 171