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 * Disable all interrupts at the legacy PIC. 37 */ 38 static void mask_all_interrupts(void) 39 { 40 outb(0xff, 0xa1); /* Mask all interrupts on the secondary PIC */ 41 io_delay(); 42 outb(0xfb, 0x21); /* Mask all but cascade on the primary PIC */ 43 io_delay(); 44 } 45 46 /* 47 * Reset IGNNE# if asserted in the FPU. 48 */ 49 static void reset_coprocessor(void) 50 { 51 outb(0, 0xf0); 52 io_delay(); 53 outb(0, 0xf1); 54 io_delay(); 55 } 56 57 /* 58 * Set up the GDT 59 */ 60 61 struct gdt_ptr { 62 u16 len; 63 u32 ptr; 64 } __attribute__((packed)); 65 66 static void setup_gdt(void) 67 { 68 /* There are machines which are known to not boot with the GDT 69 being 8-byte unaligned. Intel recommends 16 byte alignment. */ 70 static const u64 boot_gdt[] __attribute__((aligned(16))) = { 71 /* CS: code, read/execute, 4 GB, base 0 */ 72 [GDT_ENTRY_BOOT_CS] = GDT_ENTRY(0xc09b, 0, 0xfffff), 73 /* DS: data, read/write, 4 GB, base 0 */ 74 [GDT_ENTRY_BOOT_DS] = GDT_ENTRY(0xc093, 0, 0xfffff), 75 /* TSS: 32-bit tss, 104 bytes, base 4096 */ 76 /* We only have a TSS here to keep Intel VT happy; 77 we don't actually use it for anything. */ 78 [GDT_ENTRY_BOOT_TSS] = GDT_ENTRY(0x0089, 4096, 103), 79 }; 80 /* Xen HVM incorrectly stores a pointer to the gdt_ptr, instead 81 of the gdt_ptr contents. Thus, make it static so it will 82 stay in memory, at least long enough that we switch to the 83 proper kernel GDT. */ 84 static struct gdt_ptr gdt; 85 86 gdt.len = sizeof(boot_gdt)-1; 87 gdt.ptr = (u32)&boot_gdt + (ds() << 4); 88 89 asm volatile("lgdtl %0" : : "m" (gdt)); 90 } 91 92 /* 93 * Set up the IDT 94 */ 95 static void setup_idt(void) 96 { 97 static const struct gdt_ptr null_idt = {0, 0}; 98 asm volatile("lidtl %0" : : "m" (null_idt)); 99 } 100 101 /* 102 * Actual invocation sequence 103 */ 104 void go_to_protected_mode(void) 105 { 106 /* Hook before leaving real mode, also disables interrupts */ 107 realmode_switch_hook(); 108 109 /* Enable the A20 gate */ 110 if (enable_a20()) { 111 puts("A20 gate not responding, unable to boot...\n"); 112 die(); 113 } 114 115 /* Reset coprocessor (IGNNE#) */ 116 reset_coprocessor(); 117 118 /* Mask all interrupts in the PIC */ 119 mask_all_interrupts(); 120 121 /* Actual transition to protected mode... */ 122 setup_idt(); 123 setup_gdt(); 124 protected_mode_jump(boot_params.hdr.code32_start, 125 (u32)&boot_params + (ds() << 4)); 126 } 127