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linux/arch/x86_64/kernel/head.S
Zachary Amsden ffb6017563 [PATCH] x86-64: x86_64 - Fix FS/GS registers for VT execution 
Initialize FS and GS to __KERNEL_DS as well.  The actual value of them is not
important, but it is important to reload them in protected mode.  At this time,
they still retain the real mode values from initial boot.  VT disallows
execution of code under such conditions, which means hardware virtualization
can not be used to boot the kernel on Intel platforms, making the boot time
painfully slow.

This requires moving the GS load before the load of GS_BASE, so just move
all the segments loads there to keep them together in the code.

Signed-off-by: Zachary Amsden <zach@vmware.com>
Signed-off-by: Andi Kleen <ak@suse.de>
2007-02-13 13:26:24 +01:00

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/*
* linux/arch/x86_64/kernel/head.S -- start in 32bit and switch to 64bit
*
* Copyright (C) 2000 Andrea Arcangeli <andrea@suse.de> SuSE
* Copyright (C) 2000 Pavel Machek <pavel@suse.cz>
* Copyright (C) 2000 Karsten Keil <kkeil@suse.de>
* Copyright (C) 2001,2002 Andi Kleen <ak@suse.de>
*/
#include <linux/linkage.h>
#include <linux/threads.h>
#include <linux/init.h>
#include <asm/desc.h>
#include <asm/segment.h>
#include <asm/page.h>
#include <asm/msr.h>
#include <asm/cache.h>
/* we are not able to switch in one step to the final KERNEL ADRESS SPACE
* because we need identity-mapped pages on setup so define __START_KERNEL to
* 0x100000 for this stage
*
*/
.text
.section .bootstrap.text
.code32
.globl startup_32
/* %bx: 1 if coming from smp trampoline on secondary cpu */
startup_32:
/*
* At this point the CPU runs in 32bit protected mode (CS.D = 1) with
* paging disabled and the point of this file is to switch to 64bit
* long mode with a kernel mapping for kerneland to jump into the
* kernel virtual addresses.
* There is no stack until we set one up.
*/
/* Initialize the %ds segment register */
movl $__KERNEL_DS,%eax
movl %eax,%ds
/* Load new GDT with the 64bit segments using 32bit descriptor */
lgdt pGDT32 - __START_KERNEL_map
/* If the CPU doesn't support CPUID this will double fault.
* Unfortunately it is hard to check for CPUID without a stack.
*/
/* Check if extended functions are implemented */
movl $0x80000000, %eax
cpuid
cmpl $0x80000000, %eax
jbe no_long_mode
/* Check if long mode is implemented */
mov $0x80000001, %eax
cpuid
btl $29, %edx
jnc no_long_mode
/*
* Prepare for entering 64bits mode
*/
/* Enable PAE mode */
xorl %eax, %eax
btsl $5, %eax
movl %eax, %cr4
/* Setup early boot stage 4 level pagetables */
movl $(boot_level4_pgt - __START_KERNEL_map), %eax
movl %eax, %cr3
/* Setup EFER (Extended Feature Enable Register) */
movl $MSR_EFER, %ecx
rdmsr
/* Enable Long Mode */
btsl $_EFER_LME, %eax
/* Make changes effective */
wrmsr
xorl %eax, %eax
btsl $31, %eax /* Enable paging and in turn activate Long Mode */
btsl $0, %eax /* Enable protected mode */
/* Make changes effective */
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 $__KERNEL_CS, $(startup_64 - __START_KERNEL_map)
.code64
.org 0x100
.globl startup_64
startup_64:
/* We come here either from startup_32
* or directly from a 64bit bootloader.
* Since we may have come directly from a bootloader we
* reload the page tables here.
*/
/* Enable PAE mode and PGE */
xorq %rax, %rax
btsq $5, %rax
btsq $7, %rax
movq %rax, %cr4
/* Setup early boot stage 4 level pagetables. */
movq $(boot_level4_pgt - __START_KERNEL_map), %rax
movq %rax, %cr3
/* Check if nx is implemented */
movl $0x80000001, %eax
cpuid
movl %edx,%edi
/* Setup EFER (Extended Feature Enable Register) */
movl $MSR_EFER, %ecx
rdmsr
/* Enable System Call */
btsl $_EFER_SCE, %eax
/* No Execute supported? */
btl $20,%edi
jnc 1f
btsl $_EFER_NX, %eax
1:
/* Make changes effective */
wrmsr
/* Setup cr0 */
#define CR0_PM 1 /* protected mode */
#define CR0_MP (1<<1)
#define CR0_ET (1<<4)
#define CR0_NE (1<<5)
#define CR0_WP (1<<16)
#define CR0_AM (1<<18)
#define CR0_PAGING (1<<31)
movl $CR0_PM|CR0_MP|CR0_ET|CR0_NE|CR0_WP|CR0_AM|CR0_PAGING,%eax
/* Make changes effective */
movq %rax, %cr0
/* Setup a boot time stack */
movq init_rsp(%rip),%rsp
/* zero EFLAGS after setting rsp */
pushq $0
popfq
/*
* We must switch to a new descriptor in kernel space for the GDT
* because soon the kernel won't have access anymore to the userspace
* addresses where we're currently running on. We have to do that here
* because in 32bit we couldn't load a 64bit linear address.
*/
lgdt cpu_gdt_descr
/* set up data segments. actually 0 would do too */
movl $__KERNEL_DS,%eax
movl %eax,%ds
movl %eax,%ss
movl %eax,%es
/*
* We don't really need to load %fs or %gs, but load them anyway
* to kill any stale realmode selectors. This allows execution
* under VT hardware.
*/
movl %eax,%fs
movl %eax,%gs
/*
* Setup up a dummy PDA. this is just for some early bootup code
* that does in_interrupt()
*/
movl $MSR_GS_BASE,%ecx
movq $empty_zero_page,%rax
movq %rax,%rdx
shrq $32,%rdx
wrmsr
/* esi is pointer to real mode structure with interesting info.
pass it to C */
movl %esi, %edi
/* Finally jump to run C code and to be on real kernel address
* Since we are running on identity-mapped space we have to jump
* to the full 64bit address, this is only possible as indirect
* jump. In addition we need to ensure %cs is set so we make this
* a far return.
*/
movq initial_code(%rip),%rax
pushq $0 # fake return address to stop unwinder
pushq $__KERNEL_CS # set correct cs
pushq %rax # target address in negative space
lretq
/* SMP bootup changes these two */
.align 8
.globl initial_code
initial_code:
.quad x86_64_start_kernel
.globl init_rsp
init_rsp:
.quad init_thread_union+THREAD_SIZE-8
ENTRY(early_idt_handler)
cmpl $2,early_recursion_flag(%rip)
jz 1f
incl early_recursion_flag(%rip)
xorl %eax,%eax
movq 8(%rsp),%rsi # get rip
movq (%rsp),%rdx
movq %cr2,%rcx
leaq early_idt_msg(%rip),%rdi
call early_printk
cmpl $2,early_recursion_flag(%rip)
jz 1f
call dump_stack
#ifdef CONFIG_KALLSYMS
leaq early_idt_ripmsg(%rip),%rdi
movq 8(%rsp),%rsi # get rip again
call __print_symbol
#endif
1: hlt
jmp 1b
early_recursion_flag:
.long 0
early_idt_msg:
.asciz "PANIC: early exception rip %lx error %lx cr2 %lx\n"
early_idt_ripmsg:
.asciz "RIP %s\n"
.code32
ENTRY(no_long_mode)
/* This isn't an x86-64 CPU so hang */
1:
jmp 1b
.org 0xf00
.globl pGDT32
pGDT32:
.word gdt_end-cpu_gdt_table-1
.long cpu_gdt_table-__START_KERNEL_map
.org 0xf10
ljumpvector:
.long startup_64-__START_KERNEL_map
.word __KERNEL_CS
ENTRY(stext)
ENTRY(_stext)
$page = 0
#define NEXT_PAGE(name) \
$page = $page + 1; \
.org $page * 0x1000; \
phys_/**/name = $page * 0x1000 + __PHYSICAL_START; \
ENTRY(name)
NEXT_PAGE(init_level4_pgt)
/* This gets initialized in x86_64_start_kernel */
.fill 512,8,0
NEXT_PAGE(level3_ident_pgt)
.quad phys_level2_ident_pgt | 0x007
.fill 511,8,0
NEXT_PAGE(level3_kernel_pgt)
.fill 510,8,0
/* (2^48-(2*1024*1024*1024)-((2^39)*511))/(2^30) = 510 */
.quad phys_level2_kernel_pgt | 0x007
.fill 1,8,0
NEXT_PAGE(level2_ident_pgt)
/* 40MB for bootup. */
i = 0
.rept 20
.quad i << 21 | 0x083
i = i + 1
.endr
/* Temporary mappings for the super early allocator in arch/x86_64/mm/init.c */
.globl temp_boot_pmds
temp_boot_pmds:
.fill 492,8,0
NEXT_PAGE(level2_kernel_pgt)
/* 40MB kernel mapping. The kernel code cannot be bigger than that.
When you change this change KERNEL_TEXT_SIZE in page.h too. */
/* (2^48-(2*1024*1024*1024)-((2^39)*511)-((2^30)*510)) = 0 */
i = 0
.rept 20
.quad i << 21 | 0x183
i = i + 1
.endr
/* Module mapping starts here */
.fill 492,8,0
NEXT_PAGE(level3_physmem_pgt)
.quad phys_level2_kernel_pgt | 0x007 /* so that __va works even before pagetable_init */
.fill 511,8,0
#undef NEXT_PAGE
.data
#ifdef CONFIG_ACPI_SLEEP
.align PAGE_SIZE
ENTRY(wakeup_level4_pgt)
.quad phys_level3_ident_pgt | 0x007
.fill 255,8,0
.quad phys_level3_physmem_pgt | 0x007
.fill 254,8,0
/* (2^48-(2*1024*1024*1024))/(2^39) = 511 */
.quad phys_level3_kernel_pgt | 0x007
#endif
#ifndef CONFIG_HOTPLUG_CPU
__INITDATA
#endif
/*
* This default setting generates an ident mapping at address 0x100000
* and a mapping for the kernel that precisely maps virtual address
* 0xffffffff80000000 to physical address 0x000000. (always using
* 2Mbyte large pages provided by PAE mode)
*/
.align PAGE_SIZE
ENTRY(boot_level4_pgt)
.quad phys_level3_ident_pgt | 0x007
.fill 255,8,0
.quad phys_level3_physmem_pgt | 0x007
.fill 254,8,0
/* (2^48-(2*1024*1024*1024))/(2^39) = 511 */
.quad phys_level3_kernel_pgt | 0x007
.data
.align 16
.globl cpu_gdt_descr
cpu_gdt_descr:
.word gdt_end-cpu_gdt_table-1
gdt:
.quad cpu_gdt_table
#ifdef CONFIG_SMP
.rept NR_CPUS-1
.word 0
.quad 0
.endr
#endif
/* We need valid kernel segments for data and code in long mode too
* IRET will check the segment types kkeil 2000/10/28
* Also sysret mandates a special GDT layout
*/
.section .data.page_aligned, "aw"
.align PAGE_SIZE
/* The TLS descriptors are currently at a different place compared to i386.
Hopefully nobody expects them at a fixed place (Wine?) */
ENTRY(cpu_gdt_table)
.quad 0x0000000000000000 /* NULL descriptor */
.quad 0x0 /* unused */
.quad 0x00af9a000000ffff /* __KERNEL_CS */
.quad 0x00cf92000000ffff /* __KERNEL_DS */
.quad 0x00cffa000000ffff /* __USER32_CS */
.quad 0x00cff2000000ffff /* __USER_DS, __USER32_DS */
.quad 0x00affa000000ffff /* __USER_CS */
.quad 0x00cf9a000000ffff /* __KERNEL32_CS */
.quad 0,0 /* TSS */
.quad 0,0 /* LDT */
.quad 0,0,0 /* three TLS descriptors */
.quad 0x0000f40000000000 /* node/CPU stored in limit */
gdt_end:
/* asm/segment.h:GDT_ENTRIES must match this */
/* This should be a multiple of the cache line size */
/* GDTs of other CPUs are now dynamically allocated */
/* zero the remaining page */
.fill PAGE_SIZE / 8 - GDT_ENTRIES,8,0
.section .bss, "aw", @nobits
.align L1_CACHE_BYTES
ENTRY(idt_table)
.skip 256 * 16
.section .bss.page_aligned, "aw", @nobits
.align PAGE_SIZE
ENTRY(empty_zero_page)
.skip PAGE_SIZE
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