/* * * Trampoline.S Derived from Setup.S by Linus Torvalds * * 4 Jan 1997 Michael Chastain: changed to gnu as. * 15 Sept 2005 Eric Biederman: 64bit PIC support * * Entry: CS:IP point to the start of our code, we are * in real mode with no stack, but the rest of the * trampoline page to make our stack and everything else * is a mystery. * * In fact we don't actually need a stack so we don't * set one up. * * On entry to trampoline_data, the processor is in real mode * with 16-bit addressing and 16-bit data. CS has some value * and IP is zero. Thus, data addresses need to be absolute * (no relocation) and are taken with regard to r_base. * * With the addition of trampoline_level4_pgt this code can * now enter a 64bit kernel that lives at arbitrary 64bit * physical addresses. * * If you work on this file, check the object module with objdump * --full-contents --reloc to make sure there are no relocation * entries. */ #include <linux/linkage.h> #include <asm/pgtable.h> #include <asm/page.h> #include <asm/msr.h> #include <asm/segment.h> .data .code16 ENTRY(trampoline_data) r_base = . cli # We should be safe anyway wbinvd mov %cs, %ax # Code and data in the same place mov %ax, %ds mov %ax, %es mov %ax, %ss movl $0xA5A5A5A5, trampoline_data - r_base # write marker for master knows we're running # Setup stack movw $(trampoline_stack_end - r_base), %sp call verify_cpu # Verify the cpu supports long mode testl %eax, %eax # Check for return code jnz no_longmode mov %cs, %ax movzx %ax, %esi # Find the 32bit trampoline location shll $4, %esi # Fixup the vectors addl %esi, startup_32_vector - r_base addl %esi, startup_64_vector - r_base addl %esi, tgdt + 2 - r_base # Fixup the gdt pointer /* * GDT tables in non default location kernel can be beyond 16MB and * lgdt will not be able to load the address as in real mode default * operand size is 16bit. Use lgdtl instead to force operand size * to 32 bit. */ lidtl tidt - r_base # load idt with 0, 0 lgdtl tgdt - r_base # load gdt with whatever is appropriate xor %ax, %ax inc %ax # protected mode (PE) bit lmsw %ax # into protected mode # flush prefetch and jump to startup_32 ljmpl *(startup_32_vector - r_base) .code32 .balign 4 startup_32: movl $__KERNEL_DS, %eax # Initialize the %ds segment register movl %eax, %ds xorl %eax, %eax btsl $5, %eax # Enable PAE mode movl %eax, %cr4 # Setup trampoline 4 level pagetables leal (trampoline_level4_pgt - r_base)(%esi), %eax movl %eax, %cr3 movl $MSR_EFER, %ecx movl $(1 << _EFER_LME), %eax # Enable Long Mode xorl %edx, %edx wrmsr xorl %eax, %eax btsl $31, %eax # Enable paging and in turn activate Long Mode btsl $0, %eax # Enable protected mode movl %eax, %cr0 /* * At this point we're in long mode but in 32bit compatibility mode * with EFER.LME = 1, CS.L = 0, CS.D = 1 (and in turn * EFER.LMA = 1). Now we want to jump in 64bit mode, to do that we use * the new gdt/idt that has __KERNEL_CS with CS.L = 1. */ ljmp *(startup_64_vector - r_base)(%esi) .code64 .balign 4 startup_64: # Now jump into the kernel using virtual addresses movq $secondary_startup_64, %rax jmp *%rax .code16 no_longmode: hlt jmp no_longmode #include "verify_cpu.S" # Careful these need to be in the same 64K segment as the above; tidt: .word 0 # idt limit = 0 .word 0, 0 # idt base = 0L # Duplicate the global descriptor table # so the kernel can live anywhere .balign 4 tgdt: .short tgdt_end - tgdt # gdt limit .long tgdt - r_base .short 0 .quad 0x00cf9b000000ffff # __KERNEL32_CS .quad 0x00af9b000000ffff # __KERNEL_CS .quad 0x00cf93000000ffff # __KERNEL_DS tgdt_end: .balign 4 startup_32_vector: .long startup_32 - r_base .word __KERNEL32_CS, 0 .balign 4 startup_64_vector: .long startup_64 - r_base .word __KERNEL_CS, 0 trampoline_stack: .org 0x1000 trampoline_stack_end: ENTRY(trampoline_level4_pgt) .quad level3_ident_pgt - __START_KERNEL_map + _KERNPG_TABLE .fill 510,8,0 .quad level3_kernel_pgt - __START_KERNEL_map + _KERNPG_TABLE ENTRY(trampoline_end)