Re: 4.12 REGRESSION, 4.12 does not boot as VirtualBox guest

[Peter Zijlstra]

On Mon, Jun 12, 2017 at 06:51:17PM +0200, Hans de Goede wrote:
> Yes it does, with this patch the oops is back (unrelated problem) and
> the kernel boots again :)

Cheers! Full patch below.

---
Subject: Re: 4.12 REGRESSION, 4.12 does not boot as VirtualBox guest
From: Peter Zijlstra <peterz@xxxxxxxxxxxxx>
Date: Mon, 12 Jun 2017 13:52:46 +0200

Hans managed to trigger a WARN very early in the boot which killed his
(Virtual) box. Turns out we need to also consider fixup_bug() in
early_fixup_exception().

Cc: Ingo Molnar <mingo@xxxxxxxxxx>
Cc: Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx>
Cc: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
Fixes: 9a93848fe787 ("x86/debug: Implement __WARN() using UD0")
Reported-by: Hans de Goede <hdegoede@xxxxxxxxxx>
Tested-by: Hans de Goede <hdegoede@xxxxxxxxxx>
Signed-off-by: Peter Zijlstra (Intel) <peterz@xxxxxxxxxxxxx>
---
 arch/x86/include/asm/extable.h |    1 +
 arch/x86/kernel/traps.c        |    2 +-
 arch/x86/mm/extable.c          |    3 +++
 3 files changed, 5 insertions(+), 1 deletion(-)

--- a/arch/x86/include/asm/extable.h
+++ b/arch/x86/include/asm/extable.h
@@ -29,6 +29,7 @@ struct pt_regs;
 	} while (0)
 
 extern int fixup_exception(struct pt_regs *regs, int trapnr);
+extern int fixup_bug(struct pt_regs *regs, int trapnr);
 extern bool ex_has_fault_handler(unsigned long ip);
 extern void early_fixup_exception(struct pt_regs *regs, int trapnr);
 
--- a/arch/x86/kernel/traps.c
+++ b/arch/x86/kernel/traps.c
@@ -182,7 +182,7 @@ int is_valid_bugaddr(unsigned long addr)
 	return ud == INSN_UD0 || ud == INSN_UD2;
 }
 
-static int fixup_bug(struct pt_regs *regs, int trapnr)
+int fixup_bug(struct pt_regs *regs, int trapnr)
 {
 	if (trapnr != X86_TRAP_UD)
 		return 0;
--- a/arch/x86/mm/extable.c
+++ b/arch/x86/mm/extable.c
@@ -162,6 +162,9 @@ void __init early_fixup_exception(struct
 	if (fixup_exception(regs, trapnr))
 		return;
 
+	if (fixup_bug(regs, trapnr))
+		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,