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Date: Mon, 17 Aug 2015 19:04:07 +0200 (CEST)
From: Thomas Gleixner <tglx@linutronix.de>
To: Laura Abbott <labbott@redhat.com>
cc: Jiang Liu <jiang.liu@linux.intel.com>, Joerg Roedel <joro@8bytes.org>,
        Tony Luck <tony.luck@intel.com>, Borislav Petkov <bp@alien8.de>,
        javiermon@gmail.com, x86@kernel.org,
        Linux Kernel Mailing List <linux-kernel@vger.kernel.org>
Subject: Re: Boot crash with 659006b x86/x2apic: Split enable and setup
 function
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On Sun, 9 Aug 2015, Laura Abbott wrote:
> (missed the LKML cc apologies for the noise)
> 
> On 08/09/2015 06:51 AM, Laura Abbott wrote:
> > Hi,
> > 
> > We received a report[1] of an early boot crash. The reporter had difficulty
> > getting a full
> > kernel log to view and only had a screenshot which showed a crash in
> > native_apic_mem_read
> > (full screenshot available at the bugzilla along with dmesg from working
> > kernel)
> > 
> >   Bisection identified the following commit:
> > 
> > commit 659006bf3ae37a08706907ce1a36ddf57c9131d2
> > Author: Thomas Gleixner <tglx@linutronix.de>
> > Date:   Thu Jan 15 21:22:26 2015 +0000
> > 
> >      x86/x2apic: Split enable and setup function
> > 
> >      enable_x2apic() is a convoluted unreadable mess because it is used for
> >      both enablement in early boot and for setup in cpu_init().
> > 
> >      Split the code into x2apic_enable() for enablement and x2apic_setup()
> >      for setup of (secondary cpus). Make use of the new state tracking to
> >      simplify the logic.
> > 
> >      Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
> >      Cc: Jiang Liu <jiang.liu@linux.intel.com>
> >      Cc: Joerg Roedel <joro@8bytes.org>
> >      Cc: Tony Luck <tony.luck@intel.com>
> >      Cc: Borislav Petkov <bp@alien8.de>
> >      Link: http://lkml.kernel.org/r/20150115211703.129287153@linutronix.de
> >      Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
> > 
> > The report indicates that if local x2apic is disabled in the BIOS the kernel
> > boots.
> > 
> > Any ideas?

Does the patch below fix the issue?

Thanks,

	tglx

-------------------->
diff --git a/arch/x86/kernel/apic/apic.c b/arch/x86/kernel/apic/apic.c
index dcb52850a28f..339cf4fc4ca9 100644
--- a/arch/x86/kernel/apic/apic.c
+++ b/arch/x86/kernel/apic/apic.c
@@ -1424,7 +1424,7 @@ static inline void __x2apic_disable(void)
 {
 	u64 msr;
 
-	if (cpu_has_apic)
+	if (!cpu_has_apic)
 		return;
 
 	rdmsrl(MSR_IA32_APICBASE, msr);