x86/boot/pm.c

0001 // SPDX-License-Identifier: GPL-2.0-only
0002 /* -*- linux-c -*- ------------------------------------------------------- *
0003  *
0004  *   Copyright (C) 1991, 1992 Linus Torvalds
0005  *   Copyright 2007 rPath, Inc. - All Rights Reserved
0006  *
0007  * ----------------------------------------------------------------------- */
0008
0009 /*
0010  * Prepare the machine for transition to protected mode.
0011  */
0012
0013 #include "boot.h"
0014 #include <asm/segment.h>
0015
0016 /*
0017  * Invoke the realmode switch hook if present; otherwise
0018  * disable all interrupts.
0019  */
0020 static void realmode_switch_hook(void)
0021 {
0022     if (boot_params.hdr.realmode_swtch) {
0023         asm volatile("lcallw *%0"
0024                  : : "m" (boot_params.hdr.realmode_swtch)
0025                  : "eax", "ebx", "ecx", "edx");
0026     } else {
0027         asm volatile("cli");
0028         outb(0x80, 0x70); /* Disable NMI */
0029         io_delay();
0030     }
0031 }
0032
0033 /*
0034  * Disable all interrupts at the legacy PIC.
0035  */
0036 static void mask_all_interrupts(void)
0037 {
0038     outb(0xff, 0xa1);   /* Mask all interrupts on the secondary PIC */
0039     io_delay();
0040     outb(0xfb, 0x21);   /* Mask all but cascade on the primary PIC */
0041     io_delay();
0042 }
0043
0044 /*
0045  * Reset IGNNE# if asserted in the FPU.
0046  */
0047 static void reset_coprocessor(void)
0048 {
0049     outb(0, 0xf0);
0050     io_delay();
0051     outb(0, 0xf1);
0052     io_delay();
0053 }
0054
0055 /*
0056  * Set up the GDT
0057  */
0058
0059 struct gdt_ptr {
0060     u16 len;
0061     u32 ptr;
0062 } __attribute__((packed));
0063
0064 static void setup_gdt(void)
0065 {
0066     /* There are machines which are known to not boot with the GDT
0067        being 8-byte unaligned.  Intel recommends 16 byte alignment. */
0068     static const u64 boot_gdt[] __attribute__((aligned(16))) = {
0069         /* CS: code, read/execute, 4 GB, base 0 */
0070         [GDT_ENTRY_BOOT_CS] = GDT_ENTRY(0xc09b, 0, 0xfffff),
0071         /* DS: data, read/write, 4 GB, base 0 */
0072         [GDT_ENTRY_BOOT_DS] = GDT_ENTRY(0xc093, 0, 0xfffff),
0073         /* TSS: 32-bit tss, 104 bytes, base 4096 */
0074         /* We only have a TSS here to keep Intel VT happy;
0075            we don't actually use it for anything. */
0076         [GDT_ENTRY_BOOT_TSS] = GDT_ENTRY(0x0089, 4096, 103),
0077     };
0078     /* Xen HVM incorrectly stores a pointer to the gdt_ptr, instead
0079        of the gdt_ptr contents.  Thus, make it static so it will
0080        stay in memory, at least long enough that we switch to the
0081        proper kernel GDT. */
0082     static struct gdt_ptr gdt;
0083
0084     gdt.len = sizeof(boot_gdt)-1;
0085     gdt.ptr = (u32)&boot_gdt + (ds() << 4);
0086
0087     asm volatile("lgdtl %0" : : "m" (gdt));
0088 }
0089
0090 /*
0091  * Set up the IDT
0092  */
0093 static void setup_idt(void)
0094 {
0095     static const struct gdt_ptr null_idt = {0, 0};
0096     asm volatile("lidtl %0" : : "m" (null_idt));
0097 }
0098
0099 /*
0100  * Actual invocation sequence
0101  */
0102 void go_to_protected_mode(void)
0103 {
0104     /* Hook before leaving real mode, also disables interrupts */
0105     realmode_switch_hook();
0106
0107     /* Enable the A20 gate */
0108     if (enable_a20()) {
0109         puts("A20 gate not responding, unable to boot...\n");
0110         die();
0111     }
0112
0113     /* Reset coprocessor (IGNNE#) */
0114     reset_coprocessor();
0115
0116     /* Mask all interrupts in the PIC */
0117     mask_all_interrupts();
0118
0119     /* Actual transition to protected mode... */
0120     setup_idt();
0121     setup_gdt();
0122     protected_mode_jump(boot_params.hdr.code32_start,
0123                 (u32)&boot_params + (ds() << 4));
0124 }