/* SPDX-License-Identifier: GPL-2.0 */
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/*
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*
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* Trampoline.S Derived from Setup.S by Linus Torvalds
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*
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* 4 Jan 1997 Michael Chastain: changed to gnu as.
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* 15 Sept 2005 Eric Biederman: 64bit PIC support
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*
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* Entry: CS:IP point to the start of our code, we are
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* in real mode with no stack, but the rest of the
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* trampoline page to make our stack and everything else
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* is a mystery.
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*
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* On entry to trampoline_start, the processor is in real mode
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* with 16-bit addressing and 16-bit data. CS has some value
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* and IP is zero. Thus, data addresses need to be absolute
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* (no relocation) and are taken with regard to r_base.
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*
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* With the addition of trampoline_level4_pgt this code can
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* now enter a 64bit kernel that lives at arbitrary 64bit
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* physical addresses.
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*
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* If you work on this file, check the object module with objdump
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* --full-contents --reloc to make sure there are no relocation
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* entries.
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*/
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#include <linux/linkage.h>
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#include <asm/pgtable_types.h>
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#include <asm/page_types.h>
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#include <asm/msr.h>
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#include <asm/segment.h>
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#include <asm/processor-flags.h>
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#include <asm/realmode.h>
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#include "realmode.h"
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.text
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.code16
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.balign PAGE_SIZE
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ENTRY(trampoline_start)
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cli # We should be safe anyway
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wbinvd
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LJMPW_RM(1f)
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1:
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mov %cs, %ax # Code and data in the same place
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mov %ax, %ds
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mov %ax, %es
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mov %ax, %ss
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movl $0xA5A5A5A5, trampoline_status
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# write marker for master knows we're running
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# Setup stack
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movl $rm_stack_end, %esp
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call verify_cpu # Verify the cpu supports long mode
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testl %eax, %eax # Check for return code
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jnz no_longmode
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/*
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* GDT tables in non default location kernel can be beyond 16MB and
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* lgdt will not be able to load the address as in real mode default
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* operand size is 16bit. Use lgdtl instead to force operand size
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* to 32 bit.
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*/
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lidtl tr_idt # load idt with 0, 0
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lgdtl tr_gdt # load gdt with whatever is appropriate
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movw $__KERNEL_DS, %dx # Data segment descriptor
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# Enable protected mode
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movl $X86_CR0_PE, %eax # protected mode (PE) bit
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movl %eax, %cr0 # into protected mode
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# flush prefetch and jump to startup_32
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ljmpl $__KERNEL32_CS, $pa_startup_32
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no_longmode:
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hlt
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jmp no_longmode
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#include "../kernel/verify_cpu.S"
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.section ".text32","ax"
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.code32
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.balign 4
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ENTRY(startup_32)
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movl %edx, %ss
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addl $pa_real_mode_base, %esp
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movl %edx, %ds
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movl %edx, %es
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movl %edx, %fs
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movl %edx, %gs
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/*
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* Check for memory encryption support. This is a safety net in
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* case BIOS hasn't done the necessary step of setting the bit in
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* the MSR for this AP. If SME is active and we've gotten this far
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* then it is safe for us to set the MSR bit and continue. If we
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* don't we'll eventually crash trying to execute encrypted
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* instructions.
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*/
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btl $TH_FLAGS_SME_ACTIVE_BIT, pa_tr_flags
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jnc .Ldone
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movl $MSR_K8_SYSCFG, %ecx
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rdmsr
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bts $MSR_K8_SYSCFG_MEM_ENCRYPT_BIT, %eax
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jc .Ldone
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/*
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* Memory encryption is enabled but the SME enable bit for this
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* CPU has has not been set. It is safe to set it, so do so.
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*/
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wrmsr
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.Ldone:
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movl pa_tr_cr4, %eax
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movl %eax, %cr4 # Enable PAE mode
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# Setup trampoline 4 level pagetables
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movl $pa_trampoline_pgd, %eax
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movl %eax, %cr3
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# Set up EFER
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movl pa_tr_efer, %eax
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movl pa_tr_efer + 4, %edx
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movl $MSR_EFER, %ecx
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wrmsr
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# Enable paging and in turn activate Long Mode
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movl $(X86_CR0_PG | X86_CR0_WP | X86_CR0_PE), %eax
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movl %eax, %cr0
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/*
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* At this point we're in long mode but in 32bit compatibility mode
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* with EFER.LME = 1, CS.L = 0, CS.D = 1 (and in turn
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* EFER.LMA = 1). Now we want to jump in 64bit mode, to do that we use
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* the new gdt/idt that has __KERNEL_CS with CS.L = 1.
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*/
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ljmpl $__KERNEL_CS, $pa_startup_64
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.section ".text64","ax"
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.code64
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.balign 4
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ENTRY(startup_64)
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# Now jump into the kernel using virtual addresses
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jmpq *tr_start(%rip)
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.section ".rodata","a"
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# Duplicate the global descriptor table
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# so the kernel can live anywhere
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.balign 16
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.globl tr_gdt
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tr_gdt:
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.short tr_gdt_end - tr_gdt - 1 # gdt limit
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.long pa_tr_gdt
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.short 0
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.quad 0x00cf9b000000ffff # __KERNEL32_CS
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.quad 0x00af9b000000ffff # __KERNEL_CS
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.quad 0x00cf93000000ffff # __KERNEL_DS
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tr_gdt_end:
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.bss
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.balign PAGE_SIZE
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GLOBAL(trampoline_pgd) .space PAGE_SIZE
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.balign 8
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GLOBAL(trampoline_header)
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tr_start: .space 8
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GLOBAL(tr_efer) .space 8
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GLOBAL(tr_cr4) .space 4
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GLOBAL(tr_flags) .space 4
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END(trampoline_header)
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#include "trampoline_common.S"
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