[PATCH] xen: Fix x86 sched_clock() interface for xen

[PATCH] xen: Fix x86 sched_clock() interface for xen

[Juergen Gross]

Commit f94c8d11699759 ("sched/clock, x86/tsc: Rework the x86 'unstable'
sched_clock() interface") broke Xen guest time handling across
migration:

[  187.249951] Freezing user space processes ... (elapsed 0.001 seconds) done.
[  187.251137] OOM killer disabled.
[  187.251137] Freezing remaining freezable tasks ... (elapsed 0.001 seconds) done.
[  187.252299] suspending xenstore...
[  187.266987] xen:grant_table: Grant tables using version 1 layout
[18446743811.706476] OOM killer enabled.
[18446743811.706478] Restarting tasks ... done.
[18446743811.720505] Setting capacity to 16777216

Fix that by setting xen_sched_clock_offset at resume time to ensure a
monotonic clock value.

Fixes: f94c8d11699759 ("sched/clock, x86/tsc: Rework the x86 'unstable' sched_clock() interface")
Cc: <stable@vger.kernel.org> # 4.11
Reported-by: Hans van Kranenburg <hans@knorrie.org>
Signed-off-by: Juergen Gross <jgross@suse.com>
---
 arch/x86/xen/suspend.c |  4 ++++
 arch/x86/xen/time.c    | 11 +++++++++++
 arch/x86/xen/xen-ops.h |  2 ++
 3 files changed, 17 insertions(+)

diff --git a/arch/x86/xen/suspend.c b/arch/x86/xen/suspend.c
index 1d83152c761b..45fc9caf3880 100644
--- a/arch/x86/xen/suspend.c
+++ b/arch/x86/xen/suspend.c
@@ -67,6 +67,8 @@ void xen_arch_resume(void)
 {
 	int cpu;
 
+	xen_clocksource_resume();
+
 	on_each_cpu(xen_vcpu_notify_restore, NULL, 1);
 
 	for_each_online_cpu(cpu)
@@ -81,4 +83,6 @@ void xen_arch_suspend(void)
 		xen_pmu_finish(cpu);
 
 	on_each_cpu(xen_vcpu_notify_suspend, NULL, 1);
+
+	xen_clocksource_suspend();
 }
diff --git a/arch/x86/xen/time.c b/arch/x86/xen/time.c
index 72bf446c3fee..117ce958ffe6 100644
--- a/arch/x86/xen/time.c
+++ b/arch/x86/xen/time.c
@@ -32,6 +32,7 @@
 #define TIMER_SLOP	100000
 
 static u64 xen_sched_clock_offset __read_mostly;
+static u64 xen_clock_value_saved;
 
 /* Get the TSC speed from Xen */
 static unsigned long xen_tsc_khz(void)
@@ -54,6 +55,16 @@ static u64 xen_clocksource_read(void)
 	return ret;
 }
 
+void xen_clocksource_suspend(void)
+{
+	xen_clock_value_saved = xen_clocksource_read() - xen_sched_clock_offset;
+}
+
+void xen_clocksource_resume(void)
+{
+	xen_sched_clock_offset = xen_clocksource_read() - xen_clock_value_saved;
+}
+
 static u64 xen_clocksource_get_cycles(struct clocksource *cs)
 {
 	return xen_clocksource_read();
diff --git a/arch/x86/xen/xen-ops.h b/arch/x86/xen/xen-ops.h
index 0e60bd918695..a17d3bdab6b8 100644
--- a/arch/x86/xen/xen-ops.h
+++ b/arch/x86/xen/xen-ops.h
@@ -63,6 +63,8 @@ void __init xen_build_dynamic_phys_to_machine(void);
 void __init xen_vmalloc_p2m_tree(void);
 
 void xen_init_irq_ops(void);
+void xen_clocksource_suspend(void);
+void xen_clocksource_resume(void);
 void xen_setup_timer(int cpu);
 void xen_setup_runstate_info(int cpu);
 void xen_teardown_timer(int cpu);
-- 
2.16.4

Re: [PATCH] xen: Fix x86 sched_clock() interface for xen

[Boris Ostrovsky]

On 1/10/19 5:07 AM, Juergen Gross wrote:
>  
> +void xen_clocksource_suspend(void)
> +{
> +	xen_clock_value_saved = xen_clocksource_read() - xen_sched_clock_offset;


xen_clock_value_saved = xen_sched_clock() maybe? 

-boris

Re: [PATCH] xen: Fix x86 sched_clock() interface for xen

[Juergen Gross]

On 10/01/2019 16:34, Boris Ostrovsky wrote:
> On 1/10/19 5:07 AM, Juergen Gross wrote:
>>  
>> +void xen_clocksource_suspend(void)
>> +{
>> +	xen_clock_value_saved = xen_clocksource_read() - xen_sched_clock_offset;
> 
> 
> xen_clock_value_saved = xen_sched_clock() maybe? 

I wanted xen_clocksource_suspend() and xen_clocksource_resume() to
be symmetrical to each other.

In case you are feeling strong about that, I'm not. :-) So in case
you insist on it I can change it. Or you can do so while committing.


Juergen

Re: [PATCH] xen: Fix x86 sched_clock() interface for xen

[Boris Ostrovsky]

On 1/10/19 11:14 AM, Juergen Gross wrote:
> On 10/01/2019 16:34, Boris Ostrovsky wrote:
>> On 1/10/19 5:07 AM, Juergen Gross wrote:
>>>  
>>> +void xen_clocksource_suspend(void)
>>> +{
>>> +	xen_clock_value_saved = xen_clocksource_read() - xen_sched_clock_offset;
>>
>> xen_clock_value_saved = xen_sched_clock() maybe? 
> I wanted xen_clocksource_suspend() and xen_clocksource_resume() to
> be symmetrical to each other.

OK.

Reviewed-by: Boris Ostrovsky <boris.ostrovsky@oracle.com>

>
> In case you are feeling strong about that, I'm not. :-) So in case
> you insist on it I can change it. Or you can do so while committing.

Re: [PATCH] xen: Fix x86 sched_clock() interface for xen

[Boris Ostrovsky]

On 1/10/19 12:17 PM, Boris Ostrovsky wrote:
> On 1/10/19 11:14 AM, Juergen Gross wrote:
>> On 10/01/2019 16:34, Boris Ostrovsky wrote:
>>> On 1/10/19 5:07 AM, Juergen Gross wrote:
>>>>  
>>>> +void xen_clocksource_suspend(void)
>>>> +{
>>>> +	xen_clock_value_saved = xen_clocksource_read() - xen_sched_clock_offset;
>>> xen_clock_value_saved = xen_sched_clock() maybe? 
>> I wanted xen_clocksource_suspend() and xen_clocksource_resume() to
>> be symmetrical to each other.
> OK.
>
> Reviewed-by: Boris Ostrovsky <boris.ostrovsky@oracle.com>
>
>> In case you are feeling strong about that, I'm not. :-) So in case
>> you insist on it I can change it. Or you can do so while committing.


I did some basic testing and noticed this (at loglevel=8):

[   64.336488] Freezing user space processes ... (elapsed 0.001 seconds)
done.
[   64.337805] OOM killer disabled.
[   64.337814] Freezing remaining freezable tasks ... (elapsed 0.000
seconds) done.
[   64.339066] suspending xenstore...
[   85.888340] xen:grant_table: Grant tables using version 1 layout
[   64.359729] OOM killer enabled.
[   64.359736] Restarting tasks ... done.


Which made me think that perhaps we should do suspend/restore of the
clocksource as close as possible to HYPERVISOR_suspend() call, e.g. in
xen_arch_pre_suspend()/xen_arch_post_suspend():

diff --git a/arch/x86/xen/suspend.c b/arch/x86/xen/suspend.c
index 45fc9caf3880..80ecba3fcc8c 100644
--- a/arch/x86/xen/suspend.c
+++ b/arch/x86/xen/suspend.c
@@ -22,6 +22,7 @@ static DEFINE_PER_CPU(u64, spec_ctrl);
 
 void xen_arch_pre_suspend(void)
 {
+       xen_clocksource_suspend();
        xen_save_time_memory_area();
 
        if (xen_pv_domain())
@@ -36,6 +37,7 @@ void xen_arch_post_suspend(int cancelled)
                xen_hvm_post_suspend(cancelled);
 
        xen_restore_time_memory_area();
+       xen_clocksource_resume();
 }
 
 static void xen_vcpu_notify_restore(void *data)


This still has a window of incorrect clock value (you can see it, for
example, when xen_hvm_post_suspend() does pr_info("Xen HVM callback
vector for event delivery is enabled\n")), but it's smaller than before.
In particular, we will make time right before dpm_resume_start() call.

-boris

Re: [PATCH] xen: Fix x86 sched_clock() interface for xen

[Juergen Gross]

On 11/01/2019 00:10, Boris Ostrovsky wrote:
> On 1/10/19 12:17 PM, Boris Ostrovsky wrote:
>> On 1/10/19 11:14 AM, Juergen Gross wrote:
>>> On 10/01/2019 16:34, Boris Ostrovsky wrote:
>>>> On 1/10/19 5:07 AM, Juergen Gross wrote:
>>>>>  
>>>>> +void xen_clocksource_suspend(void)
>>>>> +{
>>>>> +	xen_clock_value_saved = xen_clocksource_read() - xen_sched_clock_offset;
>>>> xen_clock_value_saved = xen_sched_clock() maybe? 
>>> I wanted xen_clocksource_suspend() and xen_clocksource_resume() to
>>> be symmetrical to each other.
>> OK.
>>
>> Reviewed-by: Boris Ostrovsky <boris.ostrovsky@oracle.com>
>>
>>> In case you are feeling strong about that, I'm not. :-) So in case
>>> you insist on it I can change it. Or you can do so while committing.
> 
> 
> I did some basic testing and noticed this (at loglevel=8):
> 
> [   64.336488] Freezing user space processes ... (elapsed 0.001 seconds)
> done.
> [   64.337805] OOM killer disabled.
> [   64.337814] Freezing remaining freezable tasks ... (elapsed 0.000
> seconds) done.
> [   64.339066] suspending xenstore...
> [   85.888340] xen:grant_table: Grant tables using version 1 layout
> [   64.359729] OOM killer enabled.
> [   64.359736] Restarting tasks ... done.
> 
> 
> Which made me think that perhaps we should do suspend/restore of the
> clocksource as close as possible to HYPERVISOR_suspend() call, e.g. in
> xen_arch_pre_suspend()/xen_arch_post_suspend():
> 
> diff --git a/arch/x86/xen/suspend.c b/arch/x86/xen/suspend.c
> index 45fc9caf3880..80ecba3fcc8c 100644
> --- a/arch/x86/xen/suspend.c
> +++ b/arch/x86/xen/suspend.c
> @@ -22,6 +22,7 @@ static DEFINE_PER_CPU(u64, spec_ctrl);
>  
>  void xen_arch_pre_suspend(void)
>  {
> +       xen_clocksource_suspend();
>         xen_save_time_memory_area();
>  
>         if (xen_pv_domain())
> @@ -36,6 +37,7 @@ void xen_arch_post_suspend(int cancelled)
>                 xen_hvm_post_suspend(cancelled);
>  
>         xen_restore_time_memory_area();
> +       xen_clocksource_resume();
>  }
>  
>  static void xen_vcpu_notify_restore(void *data)
> 
> 
> This still has a window of incorrect clock value (you can see it, for
> example, when xen_hvm_post_suspend() does pr_info("Xen HVM callback
> vector for event delivery is enabled\n")), but it's smaller than before.
> In particular, we will make time right before dpm_resume_start() call.

You are right, this is better.

Sending out V2 soon.


Juergen

Re: [PATCH] xen: Fix x86 sched_clock() interface for xen

[Juergen Gross]

On 11/01/2019 08:15, Juergen Gross wrote:
> On 11/01/2019 00:10, Boris Ostrovsky wrote:
>> On 1/10/19 12:17 PM, Boris Ostrovsky wrote:
>>> On 1/10/19 11:14 AM, Juergen Gross wrote:
>>>> On 10/01/2019 16:34, Boris Ostrovsky wrote:
>>>>> On 1/10/19 5:07 AM, Juergen Gross wrote:
>>>>>>  
>>>>>> +void xen_clocksource_suspend(void)
>>>>>> +{
>>>>>> +	xen_clock_value_saved = xen_clocksource_read() - xen_sched_clock_offset;
>>>>> xen_clock_value_saved = xen_sched_clock() maybe? 
>>>> I wanted xen_clocksource_suspend() and xen_clocksource_resume() to
>>>> be symmetrical to each other.
>>> OK.
>>>
>>> Reviewed-by: Boris Ostrovsky <boris.ostrovsky@oracle.com>
>>>
>>>> In case you are feeling strong about that, I'm not. :-) So in case
>>>> you insist on it I can change it. Or you can do so while committing.
>>
>>
>> I did some basic testing and noticed this (at loglevel=8):
>>
>> [   64.336488] Freezing user space processes ... (elapsed 0.001 seconds)
>> done.
>> [   64.337805] OOM killer disabled.
>> [   64.337814] Freezing remaining freezable tasks ... (elapsed 0.000
>> seconds) done.
>> [   64.339066] suspending xenstore...
>> [   85.888340] xen:grant_table: Grant tables using version 1 layout
>> [   64.359729] OOM killer enabled.
>> [   64.359736] Restarting tasks ... done.
>>
>>
>> Which made me think that perhaps we should do suspend/restore of the
>> clocksource as close as possible to HYPERVISOR_suspend() call, e.g. in
>> xen_arch_pre_suspend()/xen_arch_post_suspend():
>>
>> diff --git a/arch/x86/xen/suspend.c b/arch/x86/xen/suspend.c
>> index 45fc9caf3880..80ecba3fcc8c 100644
>> --- a/arch/x86/xen/suspend.c
>> +++ b/arch/x86/xen/suspend.c
>> @@ -22,6 +22,7 @@ static DEFINE_PER_CPU(u64, spec_ctrl);
>>  
>>  void xen_arch_pre_suspend(void)
>>  {
>> +       xen_clocksource_suspend();
>>         xen_save_time_memory_area();
>>  
>>         if (xen_pv_domain())
>> @@ -36,6 +37,7 @@ void xen_arch_post_suspend(int cancelled)
>>                 xen_hvm_post_suspend(cancelled);
>>  
>>         xen_restore_time_memory_area();
>> +       xen_clocksource_resume();
>>  }
>>  
>>  static void xen_vcpu_notify_restore(void *data)
>>
>>
>> This still has a window of incorrect clock value (you can see it, for
>> example, when xen_hvm_post_suspend() does pr_info("Xen HVM callback
>> vector for event delivery is enabled\n")), but it's smaller than before.
>> In particular, we will make time right before dpm_resume_start() call.
> 
> You are right, this is better.

In fact, I can just handle this entirely inside arch/x86/xen/time.c by
moving the required statements into xen_save_time_memory_area() and
xen_restore_time_memory_area().


Juergen

Re: [PATCH] xen: Fix x86 sched_clock() interface for xen

[Hans van Kranenburg]

On 1/10/19 11:07 AM, Juergen Gross wrote:
> Commit f94c8d11699759 ("sched/clock, x86/tsc: Rework the x86 'unstable'
> sched_clock() interface") broke Xen guest time handling across
> migration:
> 
> [  187.249951] Freezing user space processes ... (elapsed 0.001 seconds) done.
> [  187.251137] OOM killer disabled.
> [  187.251137] Freezing remaining freezable tasks ... (elapsed 0.001 seconds) done.
> [  187.252299] suspending xenstore...
> [  187.266987] xen:grant_table: Grant tables using version 1 layout
> [18446743811.706476] OOM killer enabled.
> [18446743811.706478] Restarting tasks ... done.
> [18446743811.720505] Setting capacity to 16777216

I tried this on top of 4.19.14 (together with "x86/mm: Fix guard hole
handling", which still doesn't seem to be in 4.19) and I can confirm the
fix:

Using a PV domU,

4.19 without patch:

[  646.199018] Freezing user space processes ... (elapsed 0.002 seconds)
done.
[  646.201305] OOM killer disabled.
[  646.201311] Freezing remaining freezable tasks ... (elapsed 0.001
seconds) done.
[  646.202699] suspending xenstore...
[  646.203005] xen:grant_table: Grant tables using version 1 layout
[18446200797.089367] OOM killer enabled.
[18446200797.089382] Restarting tasks ... done.


4.19 with patch, doing live migration movement between exactly the same
set of physical servers:

[   74.878062] Freezing user space processes ... (elapsed 0.002 seconds)
done.
[   74.880308] OOM killer disabled.
[   74.880314] Freezing remaining freezable tasks ... (elapsed 0.000
seconds) done.
[   74.881681] suspending xenstore...
[   74.887497] xen:grant_table: Grant tables using version 1 layout
[   74.942011] OOM killer enabled.
[   74.942025] Restarting tasks ... done.
[   74.947688] Setting capacity to 6291456
[   74.950833] Setting capacity to 10485760

Tested-by: Hans van Kranenburg <hans@knorrie.org>

Thanks!

> 
> Fix that by setting xen_sched_clock_offset at resume time to ensure a
> monotonic clock value.
> 
> Fixes: f94c8d11699759 ("sched/clock, x86/tsc: Rework the x86 'unstable' sched_clock() interface")
> Cc: <stable@vger.kernel.org> # 4.11
> Reported-by: Hans van Kranenburg <hans@knorrie.org>
> Signed-off-by: Juergen Gross <jgross@suse.com>
> ---
>  arch/x86/xen/suspend.c |  4 ++++
>  arch/x86/xen/time.c    | 11 +++++++++++
>  arch/x86/xen/xen-ops.h |  2 ++
>  3 files changed, 17 insertions(+)
> 
> diff --git a/arch/x86/xen/suspend.c b/arch/x86/xen/suspend.c
> index 1d83152c761b..45fc9caf3880 100644
> --- a/arch/x86/xen/suspend.c
> +++ b/arch/x86/xen/suspend.c
> @@ -67,6 +67,8 @@ void xen_arch_resume(void)
>  {
>  	int cpu;
>  
> +	xen_clocksource_resume();
> +
>  	on_each_cpu(xen_vcpu_notify_restore, NULL, 1);
>  
>  	for_each_online_cpu(cpu)
> @@ -81,4 +83,6 @@ void xen_arch_suspend(void)
>  		xen_pmu_finish(cpu);
>  
>  	on_each_cpu(xen_vcpu_notify_suspend, NULL, 1);
> +
> +	xen_clocksource_suspend();
>  }
> diff --git a/arch/x86/xen/time.c b/arch/x86/xen/time.c
> index 72bf446c3fee..117ce958ffe6 100644
> --- a/arch/x86/xen/time.c
> +++ b/arch/x86/xen/time.c
> @@ -32,6 +32,7 @@
>  #define TIMER_SLOP	100000
>  
>  static u64 xen_sched_clock_offset __read_mostly;
> +static u64 xen_clock_value_saved;
>  
>  /* Get the TSC speed from Xen */
>  static unsigned long xen_tsc_khz(void)
> @@ -54,6 +55,16 @@ static u64 xen_clocksource_read(void)
>  	return ret;
>  }
>  
> +void xen_clocksource_suspend(void)
> +{
> +	xen_clock_value_saved = xen_clocksource_read() - xen_sched_clock_offset;
> +}
> +
> +void xen_clocksource_resume(void)
> +{
> +	xen_sched_clock_offset = xen_clocksource_read() - xen_clock_value_saved;
> +}
> +
>  static u64 xen_clocksource_get_cycles(struct clocksource *cs)
>  {
>  	return xen_clocksource_read();
> diff --git a/arch/x86/xen/xen-ops.h b/arch/x86/xen/xen-ops.h
> index 0e60bd918695..a17d3bdab6b8 100644
> --- a/arch/x86/xen/xen-ops.h
> +++ b/arch/x86/xen/xen-ops.h
> @@ -63,6 +63,8 @@ void __init xen_build_dynamic_phys_to_machine(void);
>  void __init xen_vmalloc_p2m_tree(void);
>  
>  void xen_init_irq_ops(void);
> +void xen_clocksource_suspend(void);
> +void xen_clocksource_resume(void);
>  void xen_setup_timer(int cpu);
>  void xen_setup_runstate_info(int cpu);
>  void xen_teardown_timer(int cpu);
>