linux-kernel - Re: commit 3c2e7f7de3 (KVM use NPT page attributes) causes boot failures

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Date:	Tue, 1 Sep 2015 21:00:07 +0800
From:	Xiao Guangrong <guangrong.xiao@...ux.intel.com>
To:	Markus Trippelsdorf <markus@...ppelsdorf.de>,
	Ingo Molnar <mingo@...nel.org>
Cc:	Linus Torvalds <torvalds@...ux-foundation.org>,
	linux-kernel@...r.kernel.org,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	Thomas Gleixner <tglx@...utronix.de>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Mike Galbraith <efault@....de>, Joerg Roedel <jroedel@...e.de>,
	Paolo Bonzini <pbonzini@...hat.com>, kvm@...r.kernel.org
Subject: Re: commit 3c2e7f7de3 (KVM use NPT page attributes) causes boot
 failures



On 09/01/2015 06:04 PM, Markus Trippelsdorf wrote:
> On 2015.09.01 at 10:56 +0200, Ingo Molnar wrote:
>>
>> * Markus Trippelsdorf <markus@...ppelsdorf.de> wrote:
>>> As I wrote in my other reply. The boot failure is nondeterministic (boot
>>> succeeds roughly every sixth time). So the bisection and the patch is
>>> just bogus (,but the boot failure is real).
>>>
>>> Sorry.
>>
>> No problem. Please let us know if any of these commits does turn out to be the
>> culprit. (Which is always a possibility.)
>
> I'm pretty sure commit 3c2e7f7de3 is the culprit.
>
> commit 3c2e7f7de3240216042b61073803b61b9b3cfb22
> Author: Paolo Bonzini <pbonzini@...hat.com>
> Date:   Tue Jul 7 14:32:17 2015 +0200
>
>      KVM: SVM: use NPT page attributes
>
> I've booted ten times in a row successfully with the following patch:
>
> diff --git a/arch/x86/kvm/svm.c b/arch/x86/kvm/svm.c
> index 74d825716f4f..3190173a575f 100644
> --- a/arch/x86/kvm/svm.c
> +++ b/arch/x86/kvm/svm.c
> @@ -989,7 +989,7 @@ static __init int svm_hardware_setup(void)
>   	} else
>   		kvm_disable_tdp();
>
> -	build_mtrr2protval();
> +//	build_mtrr2protval();
>   	return 0;
>
>   err:
>
> Paolo, your commit causes nondeterministic boot failure on my machine.
> It sometimes crashes early with the following backtrace:
>

Did it trigger the BUG()/BUG_ON() in mtrr2protval()/fallback_mtrr_type()?
If yes, could you please print the actual value out?

BTW, you may change BUG() to WARN() to get the print info more easier.

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