1 // SPDX-License-Identifier: GPL-2.0-only 2 /* -*- linux-c -*- ------------------------------------------------------- * 3 * 4 * Copyright (C) 1991, 1992 Linus Torvalds 5 * Copyright 2007 rPath, Inc. - All Rights Reserved 6 * 7 * ----------------------------------------------------------------------- */ 8 9 /* 10 * Prepare the machine for transition to protected mode. 11 */ 12 13 #include "boot.h" 14 #include <asm/segment.h> 15 16 /* 17 * Invoke the realmode switch hook if present; otherwise 18 * disable all interrupts. 19 */ 20 static void realmode_switch_hook(void) 21 { 22 if (boot_params.hdr.realmode_swtch) { 23 asm volatile("lcallw *%0" 24 : : "m" (boot_params.hdr.realmode_swtch) 25 : "eax", "ebx", "ecx", "edx"); 26 } else { 27 asm volatile("cli"); 28 outb(0x80, 0x70); /* Disable NMI */ 29 io_delay(); 30 } 31 } 32 33 /* 34 * Disable all interrupts at the legacy PIC. 35 */ 36 static void mask_all_interrupts(void) 37 { 38 outb(0xff, 0xa1); /* Mask all interrupts on the secondary PIC */ 39 io_delay(); 40 outb(0xfb, 0x21); /* Mask all but cascade on the primary PIC */ 41 io_delay(); 42 } 43 44 /* 45 * Reset IGNNE# if asserted in the FPU. 46 */ 47 static void reset_coprocessor(void) 48 { 49 outb(0, 0xf0); 50 io_delay(); 51 outb(0, 0xf1); 52 io_delay(); 53 } 54 55 /* 56 * Set up the GDT 57 */ 58 59 struct gdt_ptr { 60 u16 len; 61 u32 ptr; 62 } __attribute__((packed)); 63 64 static void setup_gdt(void) 65 { 66 /* There are machines which are known to not boot with the GDT 67 being 8-byte unaligned. Intel recommends 16 byte alignment. */ 68 static const u64 boot_gdt[] __attribute__((aligned(16))) = { 69 /* CS: code, read/execute, 4 GB, base 0 */ 70 [GDT_ENTRY_BOOT_CS] = GDT_ENTRY(0xc09b, 0, 0xfffff), 71 /* DS: data, read/write, 4 GB, base 0 */ 72 [GDT_ENTRY_BOOT_DS] = GDT_ENTRY(0xc093, 0, 0xfffff), 73 /* TSS: 32-bit tss, 104 bytes, base 4096 */ 74 /* We only have a TSS here to keep Intel VT happy; 75 we don't actually use it for anything. */ 76 [GDT_ENTRY_BOOT_TSS] = GDT_ENTRY(0x0089, 4096, 103), 77 }; 78 /* Xen HVM incorrectly stores a pointer to the gdt_ptr, instead 79 of the gdt_ptr contents. Thus, make it static so it will 80 stay in memory, at least long enough that we switch to the 81 proper kernel GDT. */ 82 static struct gdt_ptr gdt; 83 84 gdt.len = sizeof(boot_gdt)-1; 85 gdt.ptr = (u32)&boot_gdt + (ds() << 4); 86 87 asm volatile("lgdtl %0" : : "m" (gdt)); 88 } 89 90 /* 91 * Set up the IDT 92 */ 93 static void setup_idt(void) 94 { 95 static const struct gdt_ptr null_idt = {0, 0}; 96 asm volatile("lidtl %0" : : "m" (null_idt)); 97 } 98 99 /* 100 * Actual invocation sequence 101 */ 102 void go_to_protected_mode(void) 103 { 104 /* Hook before leaving real mode, also disables interrupts */ 105 realmode_switch_hook(); 106 107 /* Enable the A20 gate */ 108 if (enable_a20()) { 109 puts("A20 gate not responding, unable to boot...\n"); 110 die(); 111 } 112 113 /* Reset coprocessor (IGNNE#) */ 114 reset_coprocessor(); 115 116 /* Mask all interrupts in the PIC */ 117 mask_all_interrupts(); 118 119 /* Actual transition to protected mode... */ 120 setup_idt(); 121 setup_gdt(); 122 protected_mode_jump(boot_params.hdr.code32_start, 123 (u32)&boot_params + (ds() << 4)); 124 } 125