[Devel] [PATCH RHEL7 COMMIT] ms/x86: Extend #DF debugging aid to 64-bit

[Konstantin Khorenko]

The commit is pushed to "branch-rh7-3.10.0-957.21.3.vz7.106.x-ovz" and will appear at https://src.openvz.org/scm/ovz/vzkernel.git
after rh7-3.10.0-957.21.3.vz7.106.7
------>
commit 7bf767f0d45d569a8d1bdd885c999d8b515eeb30
Author: Borislav Petkov <bp at suse.de>
Date:   Thu May 9 12:02:29 2013 +0200

    ms/x86: Extend #DF debugging aid to 64-bit
    
    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 at suse.de>
    Link: http://lkml.kernel.org/r/1368093749-31296-1-git-send-email-bp@alien8.de
    Signed-off-by: H. Peter Anvin <hpa at linux.intel.com>
    
    (cherry picked from commit 4d067d8e056d76a3327f0517c7722db55e7888fc)
    Signed-off-by: Konstantin Khorenko <khorenko at virtuozzo.com>
---
 arch/x86/Kconfig.debug                              |  1 -
 arch/x86/include/asm/processor.h                    |  1 +
 arch/x86/kernel/Makefile                            |  2 +-
 arch/x86/kernel/{doublefault_32.c => doublefault.c} | 15 +++++++++++++++
 arch/x86/kernel/traps.c                             |  3 +++
 5 files changed, 20 insertions(+), 2 deletions(-)

diff --git a/arch/x86/Kconfig.debug b/arch/x86/Kconfig.debug
index b10368ff7bc6..c65a9ebd8629 100644
--- a/arch/x86/Kconfig.debug
+++ b/arch/x86/Kconfig.debug
@@ -158,7 +158,6 @@ config DEBUG_SET_MODULE_RONX
 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
diff --git a/arch/x86/include/asm/processor.h b/arch/x86/include/asm/processor.h
index 081ef0f7e88b..19a2cc70586e 100644
--- a/arch/x86/include/asm/processor.h
+++ b/arch/x86/include/asm/processor.h
@@ -1115,4 +1115,5 @@ extern enum mds_mitigations mds_mitigation;
 extern void (*set_cpuid_faulting_cb)(bool enable);
 extern void set_cpuid_faulting(bool enable);
 
+void df_debug(struct pt_regs *regs, long error_code);
 #endif /* _ASM_X86_PROCESSOR_H */
diff --git a/arch/x86/kernel/Makefile b/arch/x86/kernel/Makefile
index f82d5f7c3808..b5189b7c6abb 100644
--- a/arch/x86/kernel/Makefile
+++ b/arch/x86/kernel/Makefile
@@ -90,7 +90,7 @@ obj-$(CONFIG_KEXEC_FILE)	+= kexec-bzimage64.o
 obj-$(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
diff --git a/arch/x86/kernel/doublefault_32.c b/arch/x86/kernel/doublefault.c
similarity index 84%
rename from arch/x86/kernel/doublefault_32.c
rename to arch/x86/kernel/doublefault.c
index 155a13f33ed8..5d3fe8d36e4a 100644
--- a/arch/x86/kernel/doublefault_32.c
+++ b/arch/x86/kernel/doublefault.c
@@ -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
diff --git a/arch/x86/kernel/traps.c b/arch/x86/kernel/traps.c
index cf34e00e1d03..494b7d85b516 100644
--- a/arch/x86/kernel/traps.c
+++ b/arch/x86/kernel/traps.c
@@ -242,6 +242,9 @@ 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).