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

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On 09/01/2015 06:04 PM, Markus Trippelsdorf wrote:
On 2015.09.01 at 10:56 +0200, Ingo Molnar wrote:

* Markus Trippelsdorf <markus@xxxxxxxxxxxxxxx> 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@xxxxxxxxxx>
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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