[PATCH v5 3/9] x86/head: Move early exception panic code into early_fixup_exception

From: Andy Lutomirski
Date: Sat Apr 02 2016 - 10:04:18 EST

This removes a bunch of assembly and adds some C code instead. It
changes the actual printouts on both 32-bit and 64-bit kernels, but
they still seem okay.

Signed-off-by: Andy Lutomirski <luto@xxxxxxxxxx>
---
arch/x86/include/asm/uaccess.h | 2 +-
arch/x86/kernel/head_32.S | 49 +++++-------------------------------------
arch/x86/kernel/head_64.S | 45 ++------------------------------------
arch/x86/mm/extable.c | 29 ++++++++++++++++++++-----
4 files changed, 32 insertions(+), 93 deletions(-)

diff --git a/arch/x86/include/asm/uaccess.h b/arch/x86/include/asm/uaccess.h
index a3afb7259751..83fd2cf187d2 100644
--- a/arch/x86/include/asm/uaccess.h
+++ b/arch/x86/include/asm/uaccess.h
@@ -111,7 +111,7 @@ struct exception_table_entry {

extern int fixup_exception(struct pt_regs *regs, int trapnr);
extern bool ex_has_fault_handler(unsigned long ip);
-extern int early_fixup_exception(struct pt_regs *regs, int trapnr);
+extern void early_fixup_exception(struct pt_regs *regs, int trapnr);

/*
* These are the main single-value transfer routines. They automatically
diff --git a/arch/x86/kernel/head_32.S b/arch/x86/kernel/head_32.S
index 5e6ce845813a..411dce93fee9 100644
--- a/arch/x86/kernel/head_32.S
+++ b/arch/x86/kernel/head_32.S
@@ -555,8 +555,6 @@ early_idt_handler_common:
*/
cld

- cmpl $2,%ss:early_recursion_flag
- je hlt_loop
incl %ss:early_recursion_flag

/* The vector number is in pt_regs->gs */
@@ -588,13 +586,8 @@ early_idt_handler_common:
movw %gs, PT_GS(%esp)
movw $0, PT_GS+2(%esp)

- cmpl $(__KERNEL_CS),PT_CS(%esp)
- jne 10f
-
movl %esp, %eax /* args are pt_regs (EAX), trapnr (EDX) */
call early_fixup_exception
- andl %eax,%eax
- jz 10f /* Exception wasn't fixed up */

popl %ebx /* pt_regs->bx */
popl %ecx /* pt_regs->cx */
@@ -610,29 +603,6 @@ early_idt_handler_common:
decl %ss:early_recursion_flag
addl $4, %esp /* pop pt_regs->orig_ax */
iret
-
-10:
-#ifdef CONFIG_PRINTK
- xorl %eax,%eax
- movw %ax,PT_FS+2(%esp) /* clean up the segment values on some cpus */
- movw %ax,PT_DS+2(%esp)
- movw %ax,PT_ES+2(%esp)
- leal 40(%esp),%eax
- pushl %eax /* %esp before the exception */
- pushl %ebx
- pushl %ebp
- pushl %esi
- pushl %edi
- movl %cr2,%eax
- pushl %eax
- pushl (20+6*4)(%esp) /* trapno */
- pushl $fault_msg
- call printk
-#endif
- call dump_stack
-hlt_loop:
- hlt
- jmp hlt_loop
ENDPROC(early_idt_handler_common)

/* This is the default interrupt "handler" :-) */
@@ -668,10 +638,14 @@ ignore_int:
popl %eax
#endif
iret
+
+hlt_loop:
+ hlt
+ jmp hlt_loop
ENDPROC(ignore_int)
__INITDATA
.align 4
-early_recursion_flag:
+GLOBAL(early_recursion_flag)
.long 0

__REFDATA
@@ -736,19 +710,6 @@ __INITRODATA
int_msg:
.asciz "Unknown interrupt or fault at: %p %p %p\n"

-fault_msg:
-/* fault info: */
- .ascii "BUG: Int %d: CR2 %p\n"
-/* regs pushed in early_idt_handler: */
- .ascii " EDI %p ESI %p EBP %p EBX %p\n"
- .ascii " ESP %p ES %p DS %p\n"
- .ascii " EDX %p ECX %p EAX %p\n"
-/* fault frame: */
- .ascii " vec %p err %p EIP %p CS %p flg %p\n"
- .ascii "Stack: %p %p %p %p %p %p %p %p\n"
- .ascii " %p %p %p %p %p %p %p %p\n"
- .asciz " %p %p %p %p %p %p %p %p\n"
-
#include "../../x86/xen/xen-head.S"

/*
diff --git a/arch/x86/kernel/head_64.S b/arch/x86/kernel/head_64.S
index af87896b6a23..c39b6437cf03 100644
--- a/arch/x86/kernel/head_64.S
+++ b/arch/x86/kernel/head_64.S
@@ -354,8 +354,6 @@ early_idt_handler_common:
*/
cld

- cmpl $2,early_recursion_flag(%rip)
- jz 1f
incl early_recursion_flag(%rip)

/* The vector number is currently in the pt_regs->di slot. */
@@ -376,9 +374,6 @@ early_idt_handler_common:
pushq %r14 /* pt_regs->r14 */
pushq %r15 /* pt_regs->r15 */

- cmpl $__KERNEL_CS,CS(%rsp)
- jne 11f
-
cmpq $14,%rsi /* Page fault? */
jnz 10f
GET_CR2_INTO(%rdi) /* Can clobber any volatile register if pv */
@@ -389,37 +384,8 @@ early_idt_handler_common:
10:
movq %rsp,%rdi /* RDI = pt_regs; RSI is already trapnr */
call early_fixup_exception
- andl %eax,%eax
- jnz 20f # Found an exception entry
-
-11:
-#ifdef CONFIG_EARLY_PRINTK
- /*
- * On paravirt kernels, GET_CR2_INTO clobbers callee-clobbered regs.
- * We only care about RSI, so we need to save it.
- */
- movq %rsi,%rbx /* Save vector number */
- GET_CR2_INTO(%r9)
- movq ORIG_RAX(%rsp),%r8 /* error code */
- movq %rbx,%rsi /* vector number */
- movq CS(%rsp),%rdx
- movq RIP(%rsp),%rcx
- xorl %eax,%eax
- 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 RIP(%rsp),%rsi # %rip again
- call __print_symbol
-#endif
-#endif /* EARLY_PRINTK */
-1: hlt
- jmp 1b

-20: /* Exception table entry found or page table generated */
+20:
decl early_recursion_flag(%rip)
jmp restore_regs_and_iret
ENDPROC(early_idt_handler_common)
@@ -427,16 +393,9 @@ ENDPROC(early_idt_handler_common)
__INITDATA

.balign 4
-early_recursion_flag:
+GLOBAL(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:
- .asciz "RIP %s\n"
-#endif /* CONFIG_EARLY_PRINTK */
-
#define NEXT_PAGE(name) \
.balign PAGE_SIZE; \
GLOBAL(name)
diff --git a/arch/x86/mm/extable.c b/arch/x86/mm/extable.c
index d6e4e6fb4002..8997022abebc 100644
--- a/arch/x86/mm/extable.c
+++ b/arch/x86/mm/extable.c
@@ -90,8 +90,10 @@ int fixup_exception(struct pt_regs *regs, int trapnr)
return handler(e, regs, trapnr);
}

+extern unsigned int early_recursion_flag;
+
/* Restricted version used during very early boot */
-int __init early_fixup_exception(struct pt_regs *regs, int trapnr)
+void __init early_fixup_exception(struct pt_regs *regs, int trapnr)
{
const struct exception_table_entry *e;
unsigned long new_ip;
@@ -99,21 +101,38 @@ int __init early_fixup_exception(struct pt_regs *regs, int trapnr)

/* Ignore early NMIs. */
if (trapnr == X86_TRAP_NMI)
- return 1;
+ return;
+
+ if (early_recursion_flag > 2)
+ goto halt_loop;
+
+ if (regs->cs != __KERNEL_CS)
+ goto fail;

e = search_exception_tables(regs->ip);
if (!e)
- return 0;
+ goto fail;

new_ip = ex_fixup_addr(e);
handler = ex_fixup_handler(e);

/* special handling not supported during early boot */
if (handler != ex_handler_default)
- return 0;
+ goto fail;

regs->ip = new_ip;
- return 1;
+ return;
+
+fail:
+ early_printk("PANIC: early exception 0x%02x IP %lx:%lx error %lx cr2 0x%lx\n",
+ (unsigned)trapnr, (unsigned long)regs->cs, regs->ip,
+ regs->orig_ax, read_cr2());
+
+ show_regs(regs);
+
+halt_loop:
+ while (true)
+ halt();
}

/*
--
2.5.5