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

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Date:	Tue, 1 Sep 2015 12:04:17 +0200
From:	Markus Trippelsdorf <markus@...ppelsdorf.de>
To:	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 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:

map_vsyscall
kvm_arch_hardware_setup
map_vsyscall
kvm_init
map_vsyscall
do_one_initcall
kernel_init_freeable
rest_init
kernel_init
ret_from_fork
rest_init

RIP: svm_hardware_setup 

-- 
Markus
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