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/desc_defs.h> 15 #include <asm/segment.h> 16 17 /* 18 * Invoke the realmode switch hook if present; otherwise 19 * disable all interrupts. 20 */ 21 static void realmode_switch_hook(void) 22 { 23 if (boot_params.hdr.realmode_swtch) { 24 asm volatile("lcallw *%0" 25 : : "m" (boot_params.hdr.realmode_swtch) 26 : "eax", "ebx", "ecx", "edx"); 27 } else { 28 asm volatile("cli"); 29 outb(0x80, 0x70); /* Disable NMI */ 30 io_delay(); 31 } 32 } 33 34 /* 35 * Disable all interrupts at the legacy PIC. 36 */ 37 static void mask_all_interrupts(void) 38 { 39 outb(0xff, 0xa1); /* Mask all interrupts on the secondary PIC */ 40 io_delay(); 41 outb(0xfb, 0x21); /* Mask all but cascade on the primary PIC */ 42 io_delay(); 43 } 44 45 /* 46 * Reset IGNNE# if asserted in the FPU. 47 */ 48 static void reset_coprocessor(void) 49 { 50 outb(0, 0xf0); 51 io_delay(); 52 outb(0, 0xf1); 53 io_delay(); 54 } 55 56 /* 57 * Set up the GDT 58 */ 59 60 struct gdt_ptr { 61 u16 len; 62 u32 ptr; 63 } __attribute__((packed)); 64 65 static void setup_gdt(void) 66 { 67 /* There are machines which are known to not boot with the GDT 68 being 8-byte unaligned. Intel recommends 16 byte alignment. */ 69 static const u64 boot_gdt[] __attribute__((aligned(16))) = { 70 /* CS: code, read/execute, 4 GB, base 0 */ 71 [GDT_ENTRY_BOOT_CS] = GDT_ENTRY(DESC_CODE32, 0, 0xfffff), 72 /* DS: data, read/write, 4 GB, base 0 */ 73 [GDT_ENTRY_BOOT_DS] = GDT_ENTRY(DESC_DATA32, 0, 0xfffff), 74 /* TSS: 32-bit tss, 104 bytes, base 4096 */ 75 /* We only have a TSS here to keep Intel VT happy; 76 we don't actually use it for anything. */ 77 [GDT_ENTRY_BOOT_TSS] = GDT_ENTRY(DESC_TSS32, 4096, 103), 78 }; 79 /* Xen HVM incorrectly stores a pointer to the gdt_ptr, instead 80 of the gdt_ptr contents. Thus, make it static so it will 81 stay in memory, at least long enough that we switch to the 82 proper kernel GDT. */ 83 static struct gdt_ptr gdt; 84 85 gdt.len = sizeof(boot_gdt)-1; 86 gdt.ptr = (u32)&boot_gdt + (ds() << 4); 87 88 asm volatile("lgdtl %0" : : "m" (gdt)); 89 } 90 91 /* 92 * Set up the IDT 93 */ 94 static void setup_idt(void) 95 { 96 static const struct gdt_ptr null_idt = {0, 0}; 97 asm volatile("lidtl %0" : : "m" (null_idt)); 98 } 99 100 /* 101 * Actual invocation sequence 102 */ 103 void go_to_protected_mode(void) 104 { 105 /* Hook before leaving real mode, also disables interrupts */ 106 realmode_switch_hook(); 107 108 /* Enable the A20 gate */ 109 if (enable_a20()) { 110 puts("A20 gate not responding, unable to boot...\n"); 111 die(); 112 } 113 114 /* Reset coprocessor (IGNNE#) */ 115 reset_coprocessor(); 116 117 /* Mask all interrupts in the PIC */ 118 mask_all_interrupts(); 119 120 /* Actual transition to protected mode... */ 121 setup_idt(); 122 setup_gdt(); 123 protected_mode_jump(boot_params.hdr.code32_start, 124 (u32)&boot_params + (ds() << 4)); 125 } 126