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Re: [GIT PULL] scheduler changes for v4.3

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  Re: [GIT PULL] scheduler changes for v4.3 Markus Trippelsdorf <markus@trippelsdorf.de> - 2015-09-01 09:20 +0200
    Re: [GIT PULL] scheduler changes for v4.3 Ingo Molnar <mingo@kernel.org> - 2015-09-01 09:30 +0200
      Re: [GIT PULL] scheduler changes for v4.3 Markus Trippelsdorf <markus@trippelsdorf.de> - 2015-09-01 09:50 +0200
        Re: [GIT PULL] scheduler changes for v4.3 Ingo Molnar <mingo@kernel.org> - 2015-09-01 10:40 +0200
          Re: [GIT PULL] scheduler changes for v4.3 Markus Trippelsdorf <markus@trippelsdorf.de> - 2015-09-01 10:50 +0200
            Re: [GIT PULL] scheduler changes for v4.3 Ingo Molnar <mingo@kernel.org> - 2015-09-01 11:00 +0200
              Re: commit 3c2e7f7de3 (KVM use NPT page attributes) causes boot  failures Markus Trippelsdorf <markus@trippelsdorf.de> - 2015-09-01 12:10 +0200
                Re: commit 3c2e7f7de3 (KVM use NPT page attributes) causes boot  failures Xiao Guangrong <guangrong.xiao@linux.intel.com> - 2015-09-01 15:10 +0200
                  Re: commit 3c2e7f7de3 (KVM use NPT page attributes) causes boot  failures Markus Trippelsdorf <markus@trippelsdorf.de> - 2015-09-01 16:00 +0200
                    Re: commit 3c2e7f7de3 (KVM use NPT page attributes) causes boot  failures Xiao Guangrong <guangrong.xiao@linux.intel.com> - 2015-09-02 00:40 +0200
                      Re: commit 3c2e7f7de3 (KVM use NPT page attributes) causes boot  failures Markus Trippelsdorf <markus@trippelsdorf.de> - 2015-09-02 06:00 +0200
                        Re: commit 3c2e7f7de3 (KVM use NPT page attributes) causes boot  failures Xiao Guangrong <guangrong.xiao@linux.intel.com> - 2015-09-02 11:30 +0200
                          Re: commit 3c2e7f7de3 (KVM use NPT page attributes) causes boot  failures Markus Trippelsdorf <markus@trippelsdorf.de> - 2015-09-02 11:40 +0200
                            Re: commit 3c2e7f7de3 (KVM use NPT page attributes) causes boot  failures Xiao Guangrong <guangrong.xiao@linux.intel.com> - 2015-09-02 12:40 +0200
                              Re: commit 3c2e7f7de3 (KVM use NPT page attributes) causes boot  failures Markus Trippelsdorf <markus@trippelsdorf.de> - 2015-09-02 13:00 +0200
                                Re: commit 3c2e7f7de3 (KVM use NPT page attributes) causes boot  failures Xiao Guangrong <guangrong.xiao@linux.intel.com> - 2015-09-02 13:10 +0200
          Re: [GIT PULL] scheduler changes for v4.3 Markus Trippelsdorf <markus@trippelsdorf.de> - 2015-09-01 11:00 +0200
      Re: [GIT PULL] scheduler changes for v4.3 Markus Trippelsdorf <markus@trippelsdorf.de> - 2015-09-01 10:20 +0200
        Re: [GIT PULL] scheduler changes for v4.3 Markus Trippelsdorf <markus@trippelsdorf.de> - 2015-09-01 10:40 +0200

#1216639 — Re: [GIT PULL] scheduler changes for v4.3

On 2015.08.31 at 19:24 +0200, Ingo Molnar wrote:
> Please pull the latest sched-core-for-linus git tree from:
> 
>    git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip.git sched-core-for-linus
> 
>    # HEAD: ff277d4250fe715b6666219b1a3423b863418794 sched/deadline: Fix comment in enqueue_task_dl()

Linus,

your merge (commit a1d8561172f369ba) breaks booting on my machine.

I wrote down the 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

Reverting your merge resolution fixes the issue:

diff --git a/kernel/cpu.c b/kernel/cpu.c
index 82cf9dff4295..873aa0757b04 100644
--- a/kernel/cpu.c
+++ b/kernel/cpu.c
@@ -397,12 +397,11 @@ static int _cpu_down(unsigned int cpu, int tasks_frozen)
 	 * Prevent irq alloc/free while the dying cpu reorganizes the
 	 * interrupt affinities.
 	 */
-	irq_lock_sparse();
 
 	/*
 	 * So now all preempt/rcu users must observe !cpu_active().
 	 */
-	err = stop_machine(take_cpu_down, &tcd_param, cpumask_of(cpu));
+	err = __stop_machine(take_cpu_down, &tcd_param, cpumask_of(cpu));
 	if (err) {
 		/* CPU didn't die: tell everyone.  Can't complain. */
 		cpu_notify_nofail(CPU_DOWN_FAILED | mod, hcpu);

-- 
Markus
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#1216643

* Markus Trippelsdorf <markus@trippelsdorf.de> wrote:

> On 2015.08.31 at 19:24 +0200, Ingo Molnar wrote:
> > Please pull the latest sched-core-for-linus git tree from:
> > 
> >    git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip.git sched-core-for-linus
> > 
> >    # HEAD: ff277d4250fe715b6666219b1a3423b863418794 sched/deadline: Fix comment in enqueue_task_dl()
> 
> Linus,
> 
> your merge (commit a1d8561172f369ba) breaks booting on my machine.

So I just double checked Linus's merge resolution, re-created it from scratch, and 
it looks correct. Furthermore, I resolved the conflict similarly in the past and 
this resolution had been in -tip and linux-next testing for some while.

But I noticed something weird in your revert patch:

> 
> I wrote down the 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
> 
> Reverting your merge resolution fixes the issue:
> 
> diff --git a/kernel/cpu.c b/kernel/cpu.c
> index 82cf9dff4295..873aa0757b04 100644
> --- a/kernel/cpu.c
> +++ b/kernel/cpu.c
> @@ -397,12 +397,11 @@ static int _cpu_down(unsigned int cpu, int tasks_frozen)
>  	 * Prevent irq alloc/free while the dying cpu reorganizes the
>  	 * interrupt affinities.
>  	 */
> -	irq_lock_sparse();

So where does this chunk come from? None of the trees nor the merge resolution 
touches this code.

Maybe you had other changes in your tree that interfered?

That missing irq_lock_sparse() might indeed break the boot. But that's not 
something that got in there from Linus's tree AFAICS.

>  	/*
>  	 * So now all preempt/rcu users must observe !cpu_active().
>  	 */
> -	err = stop_machine(take_cpu_down, &tcd_param, cpumask_of(cpu));
> +	err = __stop_machine(take_cpu_down, &tcd_param, cpumask_of(cpu));
>  	if (err) {
>  		/* CPU didn't die: tell everyone.  Can't complain. */
>  		cpu_notify_nofail(CPU_DOWN_FAILED | mod, hcpu);

This change cannot possibly have built on Linus's tree, as __stop_machine() got 
unexported, it is now internal and static to kernel/stop_machine.c...

So could you please double check your side?

Thanks,

	Ingo
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#1216650

On 2015.09.01 at 09:27 +0200, Ingo Molnar wrote:
> 
> * Markus Trippelsdorf <markus@trippelsdorf.de> wrote:
> 
> > On 2015.08.31 at 19:24 +0200, Ingo Molnar wrote:
> > > Please pull the latest sched-core-for-linus git tree from:
> > > 
> > >    git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip.git sched-core-for-linus
> > > 
> > >    # HEAD: ff277d4250fe715b6666219b1a3423b863418794 sched/deadline: Fix comment in enqueue_task_dl()
> > 
> > Linus,
> > 
> > your merge (commit a1d8561172f369ba) breaks booting on my machine.
> 
> So I just double checked Linus's merge resolution, re-created it from scratch, and 
> it looks correct. Furthermore, I resolved the conflict similarly in the past and 
> this resolution had been in -tip and linux-next testing for some while.
> 
> But I noticed something weird in your revert patch:
> 
> > 
> > I wrote down the 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
> > 
> > Reverting your merge resolution fixes the issue:
> > 
> > diff --git a/kernel/cpu.c b/kernel/cpu.c
> > index 82cf9dff4295..873aa0757b04 100644
> > --- a/kernel/cpu.c
> > +++ b/kernel/cpu.c
> > @@ -397,12 +397,11 @@ static int _cpu_down(unsigned int cpu, int tasks_frozen)
> >  	 * Prevent irq alloc/free while the dying cpu reorganizes the
> >  	 * interrupt affinities.
> >  	 */
> > -	irq_lock_sparse();
> 
> So where does this chunk come from? None of the trees nor the merge resolution 
> touches this code.
> 
> Maybe you had other changes in your tree that interfered?
> 
> That missing irq_lock_sparse() might indeed break the boot. But that's not 
> something that got in there from Linus's tree AFAICS.
> 
> >  	/*
> >  	 * So now all preempt/rcu users must observe !cpu_active().
> >  	 */
> > -	err = stop_machine(take_cpu_down, &tcd_param, cpumask_of(cpu));
> > +	err = __stop_machine(take_cpu_down, &tcd_param, cpumask_of(cpu));
> >  	if (err) {
> >  		/* CPU didn't die: tell everyone.  Can't complain. */
> >  		cpu_notify_nofail(CPU_DOWN_FAILED | mod, hcpu);
> 
> This change cannot possibly have built on Linus's tree, as __stop_machine() got 
> unexported, it is now internal and static to kernel/stop_machine.c...
> 
> So could you please double check your side?

Well, git show a1d8561172f369ba56d636df49a6b4d6d77e2123 :

commit a1d8561172f369ba56d636df49a6b4d6d77e2123
Merge: 3959df1dfb95 ff277d4250fe
Author: Linus Torvalds <torvalds@linux-foundation.org>
Date:   Mon Aug 31 20:26:22 2015 -0700

    Merge branch 'sched-core-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip
    
    Pull scheduler updates from Ingo Molnar:
     "The biggest change in this cycle is the rewrite of the main SMP load
      balancing metric: the CPU load/utilization.  The main goal was to make
      the metric more precise and more representative - see the changelog of
      this commit for the gory details:
    
        9d89c257dfb9 ("sched/fair: Rewrite runnable load and utilization average tracking")
    
      It is done in a way that significantly reduces complexity of the code:
    
        5 files changed, 249 insertions(+), 494 deletions(-)
    
      and the performance testing results are encouraging.  Nevertheless we
      need to keep an eye on potential regressions, since this potentially
      affects every SMP workload in existence.
    
      This work comes from Yuyang Du.
    
      Other changes:
    
       - SCHED_DL updates.  (Andrea Parri)
    
       - Simplify architecture callbacks by removing finish_arch_switch().
         (Peter Zijlstra et al)
    
       - cputime accounting: guarantee stime + utime == rtime.  (Peter
         Zijlstra)
    
       - optimize idle CPU wakeups some more - inspired by Facebook server
         loads.  (Mike Galbraith)
    
       - stop_machine fixes and updates.  (Oleg Nesterov)
    
       - Introduce the 'trace_sched_waking' tracepoint.  (Peter Zijlstra)
    
       - sched/numa tweaks.  (Srikar Dronamraju)
    
       - misc fixes and small cleanups"
    
    * 'sched-core-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip: (44 commits)
      sched/deadline: Fix comment in enqueue_task_dl()
      sched/deadline: Fix comment in push_dl_tasks()
      sched: Change the sched_class::set_cpus_allowed() calling context
      sched: Make sched_class::set_cpus_allowed() unconditional
      sched: Fix a race between __kthread_bind() and sched_setaffinity()
      sched: Ensure a task has a non-normalized vruntime when returning back to CFS
      sched/numa: Fix NUMA_DIRECT topology identification
      tile: Reorganize _switch_to()
      sched, sparc32: Update scheduler comments in copy_thread()
      sched: Remove finish_arch_switch()
      sched, tile: Remove finish_arch_switch
      sched, sh: Fold finish_arch_switch() into switch_to()
      sched, score: Remove finish_arch_switch()
      sched, avr32: Remove finish_arch_switch()
      sched, MIPS: Get rid of finish_arch_switch()
      sched, arm: Remove finish_arch_switch()
      sched/fair: Clean up load average references
      sched/fair: Provide runnable_load_avg back to cfs_rq
      sched/fair: Remove task and group entity load when they are dead
      sched/fair: Init cfs_rq's sched_entity load average
      ...

diff --cc kernel/cpu.c
index 3c91a3fdfce5,664ce5299334..82cf9dff4295
--- a/kernel/cpu.c
+++ b/kernel/cpu.c
@@@ -394,15 -392,10 +394,15 @@@ static int _cpu_down(unsigned int cpu, 
  	smpboot_park_threads(cpu);
  
  	/*
 -	 * So now all preempt/rcu users must observe !cpu_active().
 +	 * Prevent irq alloc/free while the dying cpu reorganizes the
 +	 * interrupt affinities.
  	 */
 +	irq_lock_sparse();
  
 +	/*
 +	 * So now all preempt/rcu users must observe !cpu_active().
 +	 */
- 	err = __stop_machine(take_cpu_down, &tcd_param, cpumask_of(cpu));
+ 	err = stop_machine(take_cpu_down, &tcd_param, cpumask_of(cpu));
  	if (err) {
  		/* CPU didn't die: tell everyone.  Can't complain. */
  		cpu_notify_nofail(CPU_DOWN_FAILED | mod, hcpu);


-- 
Markus
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#1216683

* Markus Trippelsdorf <markus@trippelsdorf.de> wrote:

> Well, git show a1d8561172f369ba56d636df49a6b4d6d77e2123 :
> 
> commit a1d8561172f369ba56d636df49a6b4d6d77e2123
> Merge: 3959df1dfb95 ff277d4250fe
> Author: Linus Torvalds <torvalds@linux-foundation.org>
> Date:   Mon Aug 31 20:26:22 2015 -0700

> diff --cc kernel/cpu.c
> index 3c91a3fdfce5,664ce5299334..82cf9dff4295
> --- a/kernel/cpu.c
> +++ b/kernel/cpu.c
> @@@ -394,15 -392,10 +394,15 @@@ static int _cpu_down(unsigned int cpu, 
>   	smpboot_park_threads(cpu);
>   
>   	/*
>  -	 * So now all preempt/rcu users must observe !cpu_active().
>  +	 * Prevent irq alloc/free while the dying cpu reorganizes the
>  +	 * interrupt affinities.
>   	 */
>  +	irq_lock_sparse();
>   
>  +	/*
>  +	 * So now all preempt/rcu users must observe !cpu_active().
>  +	 */
> - 	err = __stop_machine(take_cpu_down, &tcd_param, cpumask_of(cpu));
> + 	err = stop_machine(take_cpu_down, &tcd_param, cpumask_of(cpu));
>   	if (err) {
>   		/* CPU didn't die: tell everyone.  Can't complain. */
>   		cpu_notify_nofail(CPU_DOWN_FAILED | mod, hcpu);

So the irq_lock_sparse() change is from a commit that got merged in the last merge 
window, which is part of v4.2:

  ce0d3c0a6fb1 ("genirq: Revert sparse irq locking around __cpu_up() and move it to x86 for now")

Could you please post the patch against Linus's latest that you have tested on 
your system to make it boot fine?

The one you posted cannot possibly build, because access to __stop_machine() is 
gone from cpu.c:

kernel/cpu.c: In function ‘_cpu_down’:
kernel/cpu.c:404:2: error: implicit declaration of function ‘__stop_machine’ [-Werror=implicit-function-declaration]
  err = __stop_machine(take_cpu_down, &tcd_param, cpumask_of(cpu));
  ^

Thanks,

	Ingo
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#1216690

On 2015.09.01 at 10:38 +0200, Ingo Molnar wrote:
> 
> * Markus Trippelsdorf <markus@trippelsdorf.de> wrote:
> 
> > Well, git show a1d8561172f369ba56d636df49a6b4d6d77e2123 :
> > 
> > commit a1d8561172f369ba56d636df49a6b4d6d77e2123
> > Merge: 3959df1dfb95 ff277d4250fe
> > Author: Linus Torvalds <torvalds@linux-foundation.org>
> > Date:   Mon Aug 31 20:26:22 2015 -0700
> 
> > diff --cc kernel/cpu.c
> > index 3c91a3fdfce5,664ce5299334..82cf9dff4295
> > --- a/kernel/cpu.c
> > +++ b/kernel/cpu.c
> > @@@ -394,15 -392,10 +394,15 @@@ static int _cpu_down(unsigned int cpu, 
> >   	smpboot_park_threads(cpu);
> >   
> >   	/*
> >  -	 * So now all preempt/rcu users must observe !cpu_active().
> >  +	 * Prevent irq alloc/free while the dying cpu reorganizes the
> >  +	 * interrupt affinities.
> >   	 */
> >  +	irq_lock_sparse();
> >   
> >  +	/*
> >  +	 * So now all preempt/rcu users must observe !cpu_active().
> >  +	 */
> > - 	err = __stop_machine(take_cpu_down, &tcd_param, cpumask_of(cpu));
> > + 	err = stop_machine(take_cpu_down, &tcd_param, cpumask_of(cpu));
> >   	if (err) {
> >   		/* CPU didn't die: tell everyone.  Can't complain. */
> >   		cpu_notify_nofail(CPU_DOWN_FAILED | mod, hcpu);
> 
> So the irq_lock_sparse() change is from a commit that got merged in the last merge 
> window, which is part of v4.2:
> 
>   ce0d3c0a6fb1 ("genirq: Revert sparse irq locking around __cpu_up() and move it to x86 for now")
> 
> Could you please post the patch against Linus's latest that you have tested on 
> your system to make it boot fine?
> 
> The one you posted cannot possibly build, because access to __stop_machine() is 
> gone from cpu.c:

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.

-- 
Markus
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#1216705

* Markus Trippelsdorf <markus@trippelsdorf.de> wrote:

> On 2015.09.01 at 10:38 +0200, Ingo Molnar wrote:
> > 
> > * Markus Trippelsdorf <markus@trippelsdorf.de> wrote:
> > 
> > > Well, git show a1d8561172f369ba56d636df49a6b4d6d77e2123 :
> > > 
> > > commit a1d8561172f369ba56d636df49a6b4d6d77e2123
> > > Merge: 3959df1dfb95 ff277d4250fe
> > > Author: Linus Torvalds <torvalds@linux-foundation.org>
> > > Date:   Mon Aug 31 20:26:22 2015 -0700
> > 
> > > diff --cc kernel/cpu.c
> > > index 3c91a3fdfce5,664ce5299334..82cf9dff4295
> > > --- a/kernel/cpu.c
> > > +++ b/kernel/cpu.c
> > > @@@ -394,15 -392,10 +394,15 @@@ static int _cpu_down(unsigned int cpu, 
> > >   	smpboot_park_threads(cpu);
> > >   
> > >   	/*
> > >  -	 * So now all preempt/rcu users must observe !cpu_active().
> > >  +	 * Prevent irq alloc/free while the dying cpu reorganizes the
> > >  +	 * interrupt affinities.
> > >   	 */
> > >  +	irq_lock_sparse();
> > >   
> > >  +	/*
> > >  +	 * So now all preempt/rcu users must observe !cpu_active().
> > >  +	 */
> > > - 	err = __stop_machine(take_cpu_down, &tcd_param, cpumask_of(cpu));
> > > + 	err = stop_machine(take_cpu_down, &tcd_param, cpumask_of(cpu));
> > >   	if (err) {
> > >   		/* CPU didn't die: tell everyone.  Can't complain. */
> > >   		cpu_notify_nofail(CPU_DOWN_FAILED | mod, hcpu);
> > 
> > So the irq_lock_sparse() change is from a commit that got merged in the last merge 
> > window, which is part of v4.2:
> > 
> >   ce0d3c0a6fb1 ("genirq: Revert sparse irq locking around __cpu_up() and move it to x86 for now")
> > 
> > Could you please post the patch against Linus's latest that you have tested on 
> > your system to make it boot fine?
> > 
> > The one you posted cannot possibly build, because access to __stop_machine() is 
> > gone from cpu.c:
> 
> 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.)

Thanks,

	Ingo
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#1216739 — 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@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 

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#1216830 — 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@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:
>

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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#1216862 — Re: commit 3c2e7f7de3 (KVM use NPT page attributes) causes boot failures

On 2015.09.01 at 21:00 +0800, Xiao Guangrong wrote:
> 
> Did it trigger the BUG()/BUG_ON() in mtrr2protval()/fallback_mtrr_type()?
> If yes, could you please print the actual value out?

It is the BUG() in fallback_mtrr_type(). I changed it to a printk and
it prints 1 for the value of mtrr.

 MTRR_TYPE_WRCOMB     1

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#1217122 — Re: commit 3c2e7f7de3 (KVM use NPT page attributes) causes boot failures

On 09/01/2015 09:56 PM, Markus Trippelsdorf wrote:
> On 2015.09.01 at 21:00 +0800, Xiao Guangrong wrote:
>>
>> Did it trigger the BUG()/BUG_ON() in mtrr2protval()/fallback_mtrr_type()?
>> If yes, could you please print the actual value out?
>
> It is the BUG() in fallback_mtrr_type(). I changed it to a printk and
> it prints 1 for the value of mtrr.
>
>   MTRR_TYPE_WRCOMB     1
>

Then I suspect pat is not enabled in your box, could you please check
CONFIG_X86_PAT is selected in your .config file, pat is shown in
/proc/cpuid, "nopat" kernel parameter is used, and dmesg | grep PAT.

I will post a fix if the suspect is right.
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#1217310 — Re: commit 3c2e7f7de3 (KVM use NPT page attributes) causes boot failures

On 2015.09.02 at 06:31 +0800, Xiao Guangrong wrote:
> 
> 
> On 09/01/2015 09:56 PM, Markus Trippelsdorf wrote:
> > On 2015.09.01 at 21:00 +0800, Xiao Guangrong wrote:
> >>
> >> Did it trigger the BUG()/BUG_ON() in mtrr2protval()/fallback_mtrr_type()?
> >> If yes, could you please print the actual value out?
> >
> > It is the BUG() in fallback_mtrr_type(). I changed it to a printk and
> > it prints 1 for the value of mtrr.
> >
> >   MTRR_TYPE_WRCOMB     1
> >
> 
> Then I suspect pat is not enabled in your box, could you please check
> CONFIG_X86_PAT is selected in your .config file, pat is shown in
> /proc/cpuid, "nopat" kernel parameter is used, and dmesg | grep PAT.

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.

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  
markus@x4 linux % cat /proc/cpuinfo| grep pat
flags           : fpu vme de pse tsc msr pae mce cx8 apic sep mtrr pge mca cmov pat pse36 clflush mmx fxsr sse sse2 ht syscall nx mmxext fxsr_opt pdpe1gb rdtscp lm 3dnowext 3dnow constant_tsc rep_good nopl nonstop_tsc extd_apicid pni monitor cx16 popcnt lahf_lm cmp_legacy svm extapic cr8_legacy abm sse4a misalignsse 3dnowprefetch osvw ibs skinit wdt hw_pstate npt lbrv svm_lock nrip_save vmmcall
...

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#1217442 — Re: commit 3c2e7f7de3 (KVM use NPT page attributes) causes boot failures

On 09/02/2015 11:50 AM, Markus Trippelsdorf wrote:
> On 2015.09.02 at 06:31 +0800, Xiao Guangrong wrote:
>>
>>
>> On 09/01/2015 09:56 PM, Markus Trippelsdorf wrote:
>>> On 2015.09.01 at 21:00 +0800, Xiao Guangrong wrote:
>>>>
>>>> Did it trigger the BUG()/BUG_ON() in mtrr2protval()/fallback_mtrr_type()?
>>>> If yes, could you please print the actual value out?
>>>
>>> It is the BUG() in fallback_mtrr_type(). I changed it to a printk and
>>> it prints 1 for the value of mtrr.
>>>
>>>    MTRR_TYPE_WRCOMB     1
>>>
>>
>> Then I suspect pat is not enabled in your box, could you please check
>> CONFIG_X86_PAT is selected in your .config file, pat is shown in
>> /proc/cpuid, "nopat" kernel parameter is used, and dmesg | grep PAT.
>
> 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?

diff --git a/arch/x86/kvm/svm.c b/arch/x86/kvm/svm.c
index 189e464..d9d3a30 100644
--- a/arch/x86/kvm/svm.c
+++ b/arch/x86/kvm/svm.c
@@ -884,6 +884,7 @@ static u8 fallback_mtrr_type(int mtrr)
         case MTRR_TYPE_WRPROT:
                 return MTRR_TYPE_UC_MINUS;
         default:
+               printk("BUG in %s, mtrr = %d.\n", __FUNCTION__, mtrr);
                 BUG();
         }
  }
@@ -907,6 +908,8 @@ static void build_mtrr2protval(void)
          * guest.
          */
         rdmsrl(MSR_IA32_CR_PAT, pat);
+       printk("KVM PAT: 0x%llx.\n", pat);
+
         for (i = 0; i < 8; i++) {
                 u8 mtrr = pat >> (8 * i);

@@ -914,10 +917,17 @@ static void build_mtrr2protval(void)
                         mtrr2protval[mtrr] = __cm_idx2pte(i);
         }

+       for (i = 0; i < 8; i++)
+               printk("mtrr2protval[%d]:%x.\n", i, mtrr2protval[i]);
+
+
         for (i = 0; i < 8; i++) {
                 if (mtrr2protval[i] == MTRR2PROTVAL_INVALID) {
                         u8 fallback = fallback_mtrr_type(i);
                         mtrr2protval[i] = mtrr2protval[fallback];
+                       if (mtrr2protval[i] == MTRR2PROTVAL_INVALID)
+                               printk("BUG in %s, mtrr2protval[%d] = %x.\n", __FUNCTION__, i, 
mtrr2protval[i]);
+
                         BUG_ON(mtrr2protval[i] == MTRR2PROTVAL_INVALID);
                 }
         }
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#1217453 — Re: commit 3c2e7f7de3 (KVM use NPT page attributes) causes boot failures

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.
[    2.138255] mtrr2protval[0]:18.
[    2.138306] mtrr2protval[1]:ff.
[    2.138356] mtrr2protval[2]:0.
[    2.138408] mtrr2protval[3]:0.
[    2.138459] mtrr2protval[4]:8.
[    2.138510] mtrr2protval[5]:ff.
[    2.138561] mtrr2protval[6]:0.
[    2.138612] mtrr2protval[7]:10.
[    2.138662] BUG in fallback_mtrr_type, mtrr = 1.

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#1217505 — Re: commit 3c2e7f7de3 (KVM use NPT page attributes) causes boot failures

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?
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#1217518 — Re: commit 3c2e7f7de3 (KVM use NPT page attributes) causes boot failures

On 2015.09.02 at 18:27 +0800, Xiao Guangrong wrote:
> 
> 
> 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.

Could it be a simple AMD/INTEL difference. I'm running a AMD CPU and I
see many !use_intel() in if statements in arch/x86/kernel/cpu/mtrr/main.c...

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#1217528 — Re: commit 3c2e7f7de3 (KVM use NPT page attributes) causes boot failures

On 09/02/2015 06:54 PM, Markus Trippelsdorf wrote:
> On 2015.09.02 at 18:27 +0800, Xiao Guangrong wrote:
>>
>>
>> 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.
>
> Could it be a simple AMD/INTEL difference. I'm running a AMD CPU and I
> see many !use_intel() in if statements in arch/x86/kernel/cpu/mtrr/main.c...
>

#define use_intel()	(mtrr_if && mtrr_if->use_intel_if == 1)

And i checked your CPU supports "mtrr" /proc/info, so it should use
generic_mtrr_ops and generic_mtrr_ops.use_intel_if = 1. That means AMD CPU
also use "intel" way. :)

Please refer to the initiation of "mtrr_if" in mtrr_bp_init().
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#1216706

On 2015.09.01 at 10:38 +0200, Ingo Molnar wrote:
> The one you posted cannot possibly build, because access to __stop_machine() is 
> gone from cpu.c:
> 
> kernel/cpu.c: In function ‘_cpu_down’:
> kernel/cpu.c:404:2: error: implicit declaration of function ‘__stop_machine’ [-Werror=implicit-function-declaration]
>   err = __stop_machine(take_cpu_down, &tcd_param, cpumask_of(cpu));

Just to clear this up: It did build on my machine because it wasn't
compiled at all (CONFIG_HOTPLUG_CPU is not set).

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#1216664

On 2015.09.01 at 09:27 +0200, Ingo Molnar wrote:
> 
> * Markus Trippelsdorf <markus@trippelsdorf.de> wrote:
> 
> > On 2015.08.31 at 19:24 +0200, Ingo Molnar wrote:
> > > Please pull the latest sched-core-for-linus git tree from:
> > > 
> > >    git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip.git sched-core-for-linus
> > > 
> > >    # HEAD: ff277d4250fe715b6666219b1a3423b863418794 sched/deadline: Fix comment in enqueue_task_dl()
> > 
> > Linus,
> > 
> > your merge (commit a1d8561172f369ba) breaks booting on my machine.
> 
> So could you please double check your side?

I just double checked and my git tree is clean. 
But it could be that the boot failure is nondeterministic, so git bisect
got off the track.

Anyway I don't have time to debug this further ATM.

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#1216684

On 2015.09.01 at 10:18 +0200, Markus Trippelsdorf wrote:
> On 2015.09.01 at 09:27 +0200, Ingo Molnar wrote:
> > 
> > * Markus Trippelsdorf <markus@trippelsdorf.de> wrote:
> > 
> > > On 2015.08.31 at 19:24 +0200, Ingo Molnar wrote:
> > > > Please pull the latest sched-core-for-linus git tree from:
> > > > 
> > > >    git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip.git sched-core-for-linus
> > > > 
> > > >    # HEAD: ff277d4250fe715b6666219b1a3423b863418794 sched/deadline: Fix comment in enqueue_task_dl()
> > > 
> > > Linus,
> > > 
> > > your merge (commit a1d8561172f369ba) breaks booting on my machine.
> > 
> > So could you please double check your side?
> 
> I just double checked and my git tree is clean. 
> But it could be that the boot failure is nondeterministic, so git bisect
> got off the track.

Just to confirm. The boot failure _is_ nondeterministic.
I just booted a few times in a row and it failed five times and
succeeded the sixth time.

So please ignore my bisection result and the bogus patch that I've
posted.

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