Messages in this thread Patch in this message | | | From | "H. Peter Anvin" <> | Subject | [PATCH 4/5] x86-64: Handle exception table entries during early boot | Date | Wed, 18 Apr 2012 17:16:49 -0700 |
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From: "H. Peter Anvin" <hpa@zytor.com>
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.
In the future it would be better to have the table sorted at compile time, or even better, turned into a perfect hash. At that point this code should be changed out from doing a linear search. --- arch/x86/include/asm/segment.h | 2 +- arch/x86/kernel/head_64.S | 72 +++++++++++++++++++++++++++++---------- 2 files changed, 54 insertions(+), 20 deletions(-)
diff --git a/arch/x86/include/asm/segment.h b/arch/x86/include/asm/segment.h index 58c1e6c..c48a950 100644 --- a/arch/x86/include/asm/segment.h +++ b/arch/x86/include/asm/segment.h @@ -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 diff --git a/arch/x86/kernel/head_64.S b/arch/x86/kernel/head_64.S index d1e112c..8b89239 100644 --- a/arch/x86/kernel/head_64.S +++ b/arch/x86/kernel/head_64.S @@ -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: + # 56(%rsp) %rflags + # 48(%rsp) %cs + # 40(%rsp) %rip + # 32(%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 # 24(%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 # 16(%rsp) + pushq %rcx # 8(%rsp) + pushq %rdx # 0(%rsp) + + cmpl $__KERNEL_CS,48(%rsp) + jne 10f + + movq 40(%rsp),%rax # %rip + leaq __start___ex_table(%rip),%rcx + leaq __stop___ex_table(%rip),%rdx + +11: + cmpq (%rcx),%rax + je 20f # Found an exception entry + addq $16,%rcx + cmpq %rdx,%rcx + jb 11b + +10: +#ifdef CONFIG_EARLY_PRINTK + GET_CR2_INTO(%r9) # can clobber any volatile register if pv + movl 32(%rsp),%r8d # error code + movl 24(%rsp),%esi # vector number + movl 48(%rsp),%edx # %cs + movq 40(%rsp),%rcx # %rip xorl %eax,%eax leaq early_idt_msg(%rip),%rdi call early_printk @@ -308,17 +331,28 @@ 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 + movq 8(%rcx),%rax # exception table target + movq %rax,40(%rsp) # change %rip on stack + 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: -- 1.7.6.5
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