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Commit 9900aa2f authored by H. Peter Anvin's avatar H. Peter Anvin Committed by H. Peter Anvin
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x86-64: Handle exception table entries during early boot 

If we get an exception during early boot, walk the exception table to
see if we should intercept it.  The main use case for this is to allow
rdmsr_safe()/wrmsr_safe() during CPU initialization.

Since the exception table is currently sorted at runtime, and fairly
late in startup, this code walks the exception table linearly.  We
obviously don't need to worry about modules, however: none have been
loaded at this point.

[ v2: Use early_fixup_exception() instead of linear search ]

Link: http://lkml.kernel.org/r/1334794610-5546-5-git-send-email-hpa@zytor.com


Signed-off-by: default avatarH. Peter Anvin <hpa@linux.intel.com>
parent 6a1ea279

arch/x86/include/asm/segment.h

+1 −1
Original line number Diff line number Diff line
@@ -213,7 +213,7 @@ 


#ifdef __KERNEL__

#ifndef __ASSEMBLY__

extern const char early_idt_handlers[NUM_EXCEPTION_VECTORS][10];

extern const char early_idt_handlers[NUM_EXCEPTION_VECTORS][2+2+5];



/*

 * Load a segment. Fall back on loading the zero

arch/x86/kernel/head_64.S

+57 −19
Original line number Diff line number Diff line
@@ -19,6 +19,7 @@ 
#include <asm/cache.h>

#include <asm/processor-flags.h>

#include <asm/percpu.h>

#include <asm/nops.h>



#ifdef CONFIG_PARAVIRT

#include <asm/asm-offsets.h>
@@ -26,6 +27,7 @@ 
#define GET_CR2_INTO(reg) GET_CR2_INTO_RAX ; movq %rax, reg

#else

#define GET_CR2_INTO(reg) movq %cr2, reg

#define INTERRUPT_RETURN iretq

#endif



/* we are not able to switch in one step to the final KERNEL ADDRESS SPACE
@@ -271,35 +273,56 @@ bad_address: 
	jmp bad_address



	.section ".init.text","ax"

#ifdef CONFIG_EARLY_PRINTK

	.globl early_idt_handlers

early_idt_handlers:

	# 104(%rsp) %rflags

	#  96(%rsp) %cs

	#  88(%rsp) %rip

	#  80(%rsp) error code

	i = 0

	.rept NUM_EXCEPTION_VECTORS

	movl $i, %esi

	.if (EXCEPTION_ERRCODE_MASK >> i) & 1

	ASM_NOP2

	.else

	pushq $0		# Dummy error code, to make stack frame uniform

	.endif

	pushq $i		# 72(%rsp) Vector number

	jmp early_idt_handler

	i = i + 1

	.endr

#endif



ENTRY(early_idt_handler)

#ifdef CONFIG_EARLY_PRINTK

	cld



	cmpl $2,early_recursion_flag(%rip)

	jz  1f

	incl early_recursion_flag(%rip)

	GET_CR2_INTO(%r9)

	xorl %r8d,%r8d		# zero for error code

	movl %esi,%ecx		# get vector number

	# Test %ecx against mask of vectors that push error code.

	cmpl $31,%ecx

	ja 0f

	movl $1,%eax

	salq %cl,%rax

	testl $EXCEPTION_ERRCODE_MASK,%eax

	je 0f

	popq %r8		# get error code

0:	movq 0(%rsp),%rcx	# get ip

	movq 8(%rsp),%rdx	# get cs



	pushq %rax		# 64(%rsp)

	pushq %rcx		# 56(%rsp)

	pushq %rdx		# 48(%rsp)

	pushq %rsi		# 40(%rsp)

	pushq %rdi		# 32(%rsp)

	pushq %r8		# 24(%rsp)

	pushq %r9		# 16(%rsp)

	pushq %r10		#  8(%rsp)

	pushq %r11		#  0(%rsp)



	cmpl $__KERNEL_CS,96(%rsp)

	jne 10f



	leaq 88(%rsp),%rdi	# Pointer to %rip

	call early_fixup_exception

	andl %eax,%eax

	jnz 20f			# Found an exception entry



10:

#ifdef CONFIG_EARLY_PRINTK

	GET_CR2_INTO(%r9)	# can clobber any volatile register if pv

	movl 80(%rsp),%r8d	# error code

	movl 72(%rsp),%esi	# vector number

	movl 96(%rsp),%edx	# %cs

	movq 88(%rsp),%rcx	# %rip

	xorl %eax,%eax

	leaq early_idt_msg(%rip),%rdi

	call early_printk
@@ -308,17 +331,32 @@ ENTRY(early_idt_handler) 
	call dump_stack

#ifdef CONFIG_KALLSYMS	

	leaq early_idt_ripmsg(%rip),%rdi

	movq 0(%rsp),%rsi	# get rip again

	movq 40(%rsp),%rsi	# %rip again

	call __print_symbol

#endif

#endif /* EARLY_PRINTK */

1:	hlt

	jmp 1b



#ifdef CONFIG_EARLY_PRINTK

20:	# Exception table entry found

	popq %r11

	popq %r10

	popq %r9

	popq %r8

	popq %rdi

	popq %rsi

	popq %rdx

	popq %rcx

	popq %rax

	addq $16,%rsp		# drop vector number and error code

	decl early_recursion_flag(%rip)

	INTERRUPT_RETURN



	.balign 4

early_recursion_flag:

	.long 0



#ifdef CONFIG_EARLY_PRINTK

early_idt_msg:

	.asciz "PANIC: early exception %02lx rip %lx:%lx error %lx cr2 %lx\n"

early_idt_ripmsg: