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Subject: Re: commit 3c2e7f7de3 (KVM use NPT page attributes) causes boot
 failures
To: Markus Trippelsdorf <markus@trippelsdorf.de>
References: <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> <55E6273D.6080701@linux.intel.com>
 <20150902035040.GA420@x4> <55E6BEB1.6080106@linux.intel.com>
 <20150902093818.GA422@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: <55E6CF13.1060806@linux.intel.com>
Date: Wed, 2 Sep 2015 18:27:31 +0800
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On 09/02/2015 05:38 PM, Markus Trippelsdorf wrote:
> On 2015.09.02 at 17:17 +0800, Xiao Guangrong wrote:
>>>
>>> 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.
>>
>> Thanks for your confirmation.
>>
>>>
>>> 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
>>
>> Strange, BP processor has already set WC to PAT1, however KVM does not read it out
>> from PAT MSR on its local CPU.
>>
>> Hmm... PAT default values do not include WC, it seems initing PAT on SP has not
>> finished after module_init()?
>>
>> Could please apply this diff and test it again?
>
> (Your patch was malformed.)
>
> [    2.138098] kvm: Nested Virtualization enabled
> [    2.138153] kvm: Nested Paging enabled
> [    2.138204] KVM PAT: 0x7040600070406.

So the PAT is the value after CPU reset, it's likely PAT is not initialized on
the local CPU.

Maybe something is escaped from stop_machine() called in native_smp_cpus_done(),
Ingo?