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x86: Extend #DF debugging aid to 64-bit

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It is sometimes very helpful to be able to pinpoint the location which
causes a double fault before it turns into a triple fault and the
machine reboots. We have this for 32-bit already so extend it to 64-bit.
On 64-bit we get the register snapshot at #DF time and not from the
first exception which actually causes the #DF. It should be close
enough, though.

[ hpa: and definitely better than nothing, which is what we have now. ]

Signed-off-by: Borislav Petkov <bp@suse.de>
Link: http://lkml.kernel.org/r/1368093749-31296-1-git-send-email-bp@alien8.de
Signed-off-by: H. Peter Anvin <hpa@linux.intel.com>
This commit is contained in:
Borislav Petkov 2013-05-09 12:02:29 +02:00 committed by H. Peter Anvin
parent f722406faa
commit 4d067d8e05
5 changed files with 20 additions and 3 deletions
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1
arch/x86/Kconfig.debug
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@ -122,7 +122,6 @@ config DEBUG_NX_TEST
config DOUBLEFAULT
default y
bool "Enable doublefault exception handler" if EXPERT
depends on X86_32
---help---
This option allows trapping of rare doublefault exceptions that
would otherwise cause a system to silently reboot. Disabling this

2
arch/x86/include/asm/processor.h
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@ -981,5 +981,5 @@ bool xen_set_default_idle(void);
#endif
void stop_this_cpu(void *dummy);
void df_debug(struct pt_regs *regs, long error_code);
#endif /* _ASM_X86_PROCESSOR_H */

2
arch/x86/kernel/Makefile
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@ -67,7 +67,7 @@ obj-$(CONFIG_KEXEC) += relocate_kernel_$(BITS).o crash.o
obj-$(CONFIG_CRASH_DUMP) += crash_dump_$(BITS).o
obj-y += kprobes/
obj-$(CONFIG_MODULES) += module.o
obj-$(CONFIG_DOUBLEFAULT) += doublefault_32.o
obj-$(CONFIG_DOUBLEFAULT) += doublefault.o
obj-$(CONFIG_KGDB) += kgdb.o
obj-$(CONFIG_VM86) += vm86_32.o
obj-$(CONFIG_EARLY_PRINTK) += early_printk.o

15
arch/x86/kernel/doublefault_32.c → arch/x86/kernel/doublefault.c
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@ -9,6 +9,8 @@
#include <asm/processor.h>
#include <asm/desc.h>
#ifdef CONFIG_X86_32
#define DOUBLEFAULT_STACKSIZE (1024)
static unsigned long doublefault_stack[DOUBLEFAULT_STACKSIZE];
#define STACK_START (unsigned long)(doublefault_stack+DOUBLEFAULT_STACKSIZE)
@ -67,3 +69,16 @@ struct tss_struct doublefault_tss __cacheline_aligned = {
.__cr3 = __pa_nodebug(swapper_pg_dir),
}
};
/* dummy for do_double_fault() call */
void df_debug(struct pt_regs *regs, long error_code) {}
#else /* !CONFIG_X86_32 */
void df_debug(struct pt_regs *regs, long error_code)
{
pr_emerg("PANIC: double fault, error_code: 0x%lx\n", error_code);
show_regs(regs);
panic("Machine halted.");
}
#endif

3
arch/x86/kernel/traps.c
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@ -254,6 +254,9 @@ dotraplinkage void do_double_fault(struct pt_regs *regs, long error_code)
tsk->thread.error_code = error_code;
tsk->thread.trap_nr = X86_TRAP_DF;
#ifdef CONFIG_DOUBLEFAULT
df_debug(regs, error_code);
#endif
/*
* This is always a kernel trap and never fixable (and thus must
* never return).