linux-kernel - Re: 4.12 REGRESSION, 4.12 does not boot as VirtualBox guest

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Date:   Mon, 12 Jun 2017 13:52:46 +0200
From:   Peter Zijlstra <peterz@...radead.org>
To:     Thomas Gleixner <tglx@...utronix.de>
Cc:     Linus Torvalds <torvalds@...ux-foundation.org>,
        Hans de Goede <hdegoede@...hat.com>,
        Ingo Molnar <mingo@...nel.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        the arch/x86 maintainers <x86@...nel.org>
Subject: Re: 4.12 REGRESSION, 4.12 does not boot as VirtualBox guest

On Mon, Jun 12, 2017 at 10:16:53AM +0200, Thomas Gleixner wrote:
> On Sat, 10 Jun 2017, Linus Torvalds wrote:
> 
> > On Fri, Jun 9, 2017 at 3:33 AM, Hans de Goede <hdegoede@...hat.com> wrote:
> > >
> > > Sorry for escalating this right up to you, but this issue
> > > does not seem to be getting any attention and I'm not sure
> > > which subsys maintainer to poke about this.
> > 
> > Looks like x86. Added people.
> > 
> > > The problem is that the 4.12-rc# kernels fail to boot on
> > > VirtualBox guests hosted on any machine with a Sky Lake
> > > (and probably also a Kaby Lake) CPU, for details see:
> > >
> > > https://bugzilla.kernel.org/show_bug.cgi?id=195961
> 
> Looks like the WARN/BUG rework. Peter????

I wasn't aware we'd call WARN _that_ early. Does something like so make
it work?

---
 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(-)

diff --git a/arch/x86/include/asm/extable.h b/arch/x86/include/asm/extable.h
index b8ad261d11dc..c66d19e3c23e 100644
--- 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);
 
diff --git a/arch/x86/kernel/traps.c b/arch/x86/kernel/traps.c
index 3995d3a777d4..bf54309b85da 100644
--- 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;
diff --git a/arch/x86/mm/extable.c b/arch/x86/mm/extable.c
index 35ea061010a1..0ea8afcb929c 100644
--- a/arch/x86/mm/extable.c
+++ b/arch/x86/mm/extable.c
@@ -162,6 +162,9 @@ void __init early_fixup_exception(struct pt_regs *regs, int trapnr)
 	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,