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124 lines
2.9 KiB
124 lines
2.9 KiB
// SPDX-License-Identifier: GPL-2.0-only |
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/* -*- linux-c -*- ------------------------------------------------------- * |
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* |
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* Copyright (C) 1991, 1992 Linus Torvalds |
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* Copyright 2007 rPath, Inc. - All Rights Reserved |
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* |
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* ----------------------------------------------------------------------- */ |
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/* |
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* Prepare the machine for transition to protected mode. |
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*/ |
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#include "boot.h" |
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#include <asm/segment.h> |
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/* |
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* Invoke the realmode switch hook if present; otherwise |
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* disable all interrupts. |
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*/ |
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static void realmode_switch_hook(void) |
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{ |
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if (boot_params.hdr.realmode_swtch) { |
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asm volatile("lcallw *%0" |
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: : "m" (boot_params.hdr.realmode_swtch) |
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: "eax", "ebx", "ecx", "edx"); |
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} else { |
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asm volatile("cli"); |
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outb(0x80, 0x70); /* Disable NMI */ |
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io_delay(); |
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} |
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} |
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/* |
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* Disable all interrupts at the legacy PIC. |
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*/ |
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static void mask_all_interrupts(void) |
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{ |
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outb(0xff, 0xa1); /* Mask all interrupts on the secondary PIC */ |
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io_delay(); |
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outb(0xfb, 0x21); /* Mask all but cascade on the primary PIC */ |
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io_delay(); |
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} |
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/* |
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* Reset IGNNE# if asserted in the FPU. |
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*/ |
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static void reset_coprocessor(void) |
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{ |
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outb(0, 0xf0); |
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io_delay(); |
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outb(0, 0xf1); |
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io_delay(); |
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} |
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/* |
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* Set up the GDT |
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*/ |
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struct gdt_ptr { |
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u16 len; |
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u32 ptr; |
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} __attribute__((packed)); |
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static void setup_gdt(void) |
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{ |
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/* There are machines which are known to not boot with the GDT |
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being 8-byte unaligned. Intel recommends 16 byte alignment. */ |
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static const u64 boot_gdt[] __attribute__((aligned(16))) = { |
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/* CS: code, read/execute, 4 GB, base 0 */ |
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[GDT_ENTRY_BOOT_CS] = GDT_ENTRY(0xc09b, 0, 0xfffff), |
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/* DS: data, read/write, 4 GB, base 0 */ |
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[GDT_ENTRY_BOOT_DS] = GDT_ENTRY(0xc093, 0, 0xfffff), |
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/* TSS: 32-bit tss, 104 bytes, base 4096 */ |
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/* We only have a TSS here to keep Intel VT happy; |
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we don't actually use it for anything. */ |
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[GDT_ENTRY_BOOT_TSS] = GDT_ENTRY(0x0089, 4096, 103), |
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}; |
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/* Xen HVM incorrectly stores a pointer to the gdt_ptr, instead |
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of the gdt_ptr contents. Thus, make it static so it will |
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stay in memory, at least long enough that we switch to the |
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proper kernel GDT. */ |
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static struct gdt_ptr gdt; |
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gdt.len = sizeof(boot_gdt)-1; |
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gdt.ptr = (u32)&boot_gdt + (ds() << 4); |
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asm volatile("lgdtl %0" : : "m" (gdt)); |
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} |
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/* |
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* Set up the IDT |
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*/ |
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static void setup_idt(void) |
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{ |
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static const struct gdt_ptr null_idt = {0, 0}; |
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asm volatile("lidtl %0" : : "m" (null_idt)); |
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} |
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/* |
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* Actual invocation sequence |
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*/ |
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void go_to_protected_mode(void) |
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{ |
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/* Hook before leaving real mode, also disables interrupts */ |
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realmode_switch_hook(); |
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/* Enable the A20 gate */ |
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if (enable_a20()) { |
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puts("A20 gate not responding, unable to boot...\n"); |
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die(); |
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} |
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/* Reset coprocessor (IGNNE#) */ |
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reset_coprocessor(); |
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/* Mask all interrupts in the PIC */ |
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mask_all_interrupts(); |
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/* Actual transition to protected mode... */ |
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setup_idt(); |
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setup_gdt(); |
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protected_mode_jump(boot_params.hdr.code32_start, |
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(u32)&boot_params + (ds() << 4)); |
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}
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