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

Markus Trippelsdorf
2015-09-01T10:04:22Z

On 2015.09.01 at 10:56 +0200, Ingo Molnar wrote:
>
> * Markus Trippelsdorf <markus@trippelsdorf.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@redhat.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