1/* SPDX-License-Identifier: GPL-2.0 */ 2/* 3 * 4 * Trampoline.S Derived from Setup.S by Linus Torvalds 5 * 6 * 4 Jan 1997 Michael Chastain: changed to gnu as. 7 * 15 Sept 2005 Eric Biederman: 64bit PIC support 8 * 9 * Entry: CS:IP point to the start of our code, we are 10 * in real mode with no stack, but the rest of the 11 * trampoline page to make our stack and everything else 12 * is a mystery. 13 * 14 * On entry to trampoline_start, the processor is in real mode 15 * with 16-bit addressing and 16-bit data. CS has some value 16 * and IP is zero. Thus, data addresses need to be absolute 17 * (no relocation) and are taken with regard to r_base. 18 * 19 * With the addition of trampoline_level4_pgt this code can 20 * now enter a 64bit kernel that lives at arbitrary 64bit 21 * physical addresses. 22 * 23 * If you work on this file, check the object module with objdump 24 * --full-contents --reloc to make sure there are no relocation 25 * entries. 26 */ 27 28#include <linux/linkage.h> 29#include <asm/pgtable_types.h> 30#include <asm/page_types.h> 31#include <asm/msr.h> 32#include <asm/segment.h> 33#include <asm/processor-flags.h> 34#include <asm/realmode.h> 35#include "realmode.h" 36 37 .text 38 .code16 39 40 .balign PAGE_SIZE 41ENTRY(trampoline_start) 42 cli # We should be safe anyway 43 wbinvd 44 45 LJMPW_RM(1f) 461: 47 mov %cs, %ax # Code and data in the same place 48 mov %ax, %ds 49 mov %ax, %es 50 mov %ax, %ss 51 52 # Setup stack 53 movl $rm_stack_end, %esp 54 55 call verify_cpu # Verify the cpu supports long mode 56 testl %eax, %eax # Check for return code 57 jnz no_longmode 58 59 /* 60 * GDT tables in non default location kernel can be beyond 16MB and 61 * lgdt will not be able to load the address as in real mode default 62 * operand size is 16bit. Use lgdtl instead to force operand size 63 * to 32 bit. 64 */ 65 66 lidtl tr_idt # load idt with 0, 0 67 lgdtl tr_gdt # load gdt with whatever is appropriate 68 69 movw $__KERNEL_DS, %dx # Data segment descriptor 70 71 # Enable protected mode 72 movl $X86_CR0_PE, %eax # protected mode (PE) bit 73 movl %eax, %cr0 # into protected mode 74 75 # flush prefetch and jump to startup_32 76 ljmpl $__KERNEL32_CS, $pa_startup_32 77 78no_longmode: 79 hlt 80 jmp no_longmode 81#include "../kernel/verify_cpu.S" 82 83 .section ".text32","ax" 84 .code32 85 .balign 4 86ENTRY(startup_32) 87 movl %edx, %ss 88 addl $pa_real_mode_base, %esp 89 movl %edx, %ds 90 movl %edx, %es 91 movl %edx, %fs 92 movl %edx, %gs 93 94 /* 95 * Check for memory encryption support. This is a safety net in 96 * case BIOS hasn't done the necessary step of setting the bit in 97 * the MSR for this AP. If SME is active and we've gotten this far 98 * then it is safe for us to set the MSR bit and continue. If we 99 * don't we'll eventually crash trying to execute encrypted 100 * instructions. 101 */ 102 btl $TH_FLAGS_SME_ACTIVE_BIT, pa_tr_flags 103 jnc .Ldone 104 movl $MSR_K8_SYSCFG, %ecx 105 rdmsr 106 bts $MSR_K8_SYSCFG_MEM_ENCRYPT_BIT, %eax 107 jc .Ldone 108 109 /* 110 * Memory encryption is enabled but the SME enable bit for this 111 * CPU has has not been set. It is safe to set it, so do so. 112 */ 113 wrmsr 114.Ldone: 115 116 movl pa_tr_cr4, %eax 117 movl %eax, %cr4 # Enable PAE mode 118 119 # Setup trampoline 4 level pagetables 120 movl $pa_trampoline_pgd, %eax 121 movl %eax, %cr3 122 123 # Set up EFER 124 movl pa_tr_efer, %eax 125 movl pa_tr_efer + 4, %edx 126 movl $MSR_EFER, %ecx 127 wrmsr 128 129 # Enable paging and in turn activate Long Mode 130 movl $(X86_CR0_PG | X86_CR0_WP | X86_CR0_PE), %eax 131 movl %eax, %cr0 132 133 /* 134 * At this point we're in long mode but in 32bit compatibility mode 135 * with EFER.LME = 1, CS.L = 0, CS.D = 1 (and in turn 136 * EFER.LMA = 1). Now we want to jump in 64bit mode, to do that we use 137 * the new gdt/idt that has __KERNEL_CS with CS.L = 1. 138 */ 139 ljmpl $__KERNEL_CS, $pa_startup_64 140 141 .section ".text64","ax" 142 .code64 143 .balign 4 144ENTRY(startup_64) 145 # Now jump into the kernel using virtual addresses 146 jmpq *tr_start(%rip) 147 148 .section ".rodata","a" 149 # Duplicate the global descriptor table 150 # so the kernel can live anywhere 151 .balign 16 152 .globl tr_gdt 153tr_gdt: 154 .short tr_gdt_end - tr_gdt - 1 # gdt limit 155 .long pa_tr_gdt 156 .short 0 157 .quad 0x00cf9b000000ffff # __KERNEL32_CS 158 .quad 0x00af9b000000ffff # __KERNEL_CS 159 .quad 0x00cf93000000ffff # __KERNEL_DS 160tr_gdt_end: 161 162 .bss 163 .balign PAGE_SIZE 164GLOBAL(trampoline_pgd) .space PAGE_SIZE 165 166 .balign 8 167GLOBAL(trampoline_header) 168 tr_start: .space 8 169 GLOBAL(tr_efer) .space 8 170 GLOBAL(tr_cr4) .space 4 171 GLOBAL(tr_flags) .space 4 172END(trampoline_header) 173 174#include "trampoline_common.S" 175