From mboxrd@z Thu Jan  1 00:00:00 1970
From: Markus Trippelsdorf <markus@trippelsdorf.de>
Subject: Re: commit 3c2e7f7de3 (KVM use NPT page attributes) causes boot
 failures
Date: Wed, 2 Sep 2015 05:50:40 +0200
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Cc: Ingo Molnar <mingo@kernel.org>,
	Linus Torvalds <torvalds@linux-foundation.org>,
	linux-kernel@vger.kernel.org,
	Peter Zijlstra <a.p.zijlstra@chello.nl>,
	Thomas Gleixner <tglx@linutronix.de>,
	Andrew Morton <akpm@linux-foundation.org>,
	Mike Galbraith <efault@gmx.de>, Joerg Roedel <jroedel@suse.de>,
	Paolo Bonzini <pbonzini@redhat.com>, kvm@vger.kernel.org
To: Xiao Guangrong <guangrong.xiao@linux.intel.com>
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List-Id: kvm.vger.kernel.org

On 2015.09.02 at 06:31 +0800, Xiao Guangrong wrote:
> 
> 
> On 09/01/2015 09:56 PM, Markus Trippelsdorf wrote:
> > On 2015.09.01 at 21:00 +0800, Xiao Guangrong wrote:
> >>
> >> Did it trigger the BUG()/BUG_ON() in mtrr2protval()/fallback_mtrr_type()?
> >> If yes, could you please print the actual value out?
> >
> > It is the BUG() in fallback_mtrr_type(). I changed it to a printk and
> > it prints 1 for the value of mtrr.
> >
> >   MTRR_TYPE_WRCOMB     1
> >
> 
> Then I suspect pat is not enabled in your box, could you please check
> CONFIG_X86_PAT is selected in your .config file, pat is shown in
> /proc/cpuid, "nopat" kernel parameter is used, and dmesg | grep PAT.

No. PAT is of course enabled and booting is successful sometimes even
with the BUG() in allback_mtrr_type(). I suspect a setup (timing) issue.

markus@x4 linux % cat .config | grep  X86_PAT
CONFIG_X86_PAT=y
markus@x4 linux % dmesg | grep PAT
[    0.000000] x86/PAT: Configuration [0-7]: WB  WC  UC- UC  WB  WC  UC- WT  
markus@x4 linux % cat /proc/cpuinfo| grep pat
flags           : fpu vme de pse tsc msr pae mce cx8 apic sep mtrr pge mca cmov pat pse36 clflush mmx fxsr sse sse2 ht syscall nx mmxext fxsr_opt pdpe1gb rdtscp lm 3dnowext 3dnow constant_tsc rep_good nopl nonstop_tsc extd_apicid pni monitor cx16 popcnt lahf_lm cmp_legacy svm extapic cr8_legacy abm sse4a misalignsse 3dnowprefetch osvw ibs skinit wdt hw_pstate npt lbrv svm_lock nrip_save vmmcall
...

-- 
Markus