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Subject: Re: commit 3c2e7f7de3 (KVM use NPT page attributes) causes boot
 failures
To: Markus Trippelsdorf <markus@trippelsdorf.de>
References: <20150831172453.GA5429@gmail.com> <20150901070856.GA430@x4>
 <20150901072741.GB20383@gmail.com> <20150901074449.GB430@x4>
 <20150901083856.GD25398@gmail.com> <20150901084444.GB421@x4>
 <20150901085627.GF6315@gmail.com> <20150901100417.GA424@x4>
 <55E5A157.5040403@linux.intel.com> <20150901135636.GA423@x4>
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
From: Xiao Guangrong <guangrong.xiao@linux.intel.com>
Message-ID: <55E6273D.6080701@linux.intel.com>
Date: Wed, 2 Sep 2015 06:31:25 +0800
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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.

I will post a fix if the suspect is right.