[PATCH v6 0/2] x86/apic: x2apic write eoi msr notrace

[PATCH v6 0/2] x86/apic: x2apic write eoi msr notrace

[Wanpeng Li]

| RCU used illegally from idle CPU!
| rcu_scheduler_active = 1, debug_locks = 0
| RCU used illegally from extended quiescent state!
| no locks held by swapper/1/0.
| 
|  [<ffffffff9d492b95>] do_trace_write_msr+0x135/0x140
|  [<ffffffff9d06f860>] native_write_msr+0x20/0x30
|  [<ffffffff9d065fad>] native_apic_msr_eoi_write+0x1d/0x30
|  [<ffffffff9d05bd1d>] smp_reschedule_interrupt+0x1d/0x30
|  [<ffffffff9d8daec6>] reschedule_interrupt+0x96/0xa0

Reschedule interrupt may be called in cpu idle state. This causes lockdep
check warning above.

As Peterz pointed out:

| The thing is, many many smp_reschedule_interrupt() invocations don't
| actually execute anything much at all and are only send to tickle the
| return to user path (which does the actual preemption).
| 
| Having to do the whole irq_enter/irq_exit dance just for this unlikely
| debug case totally blows.

This patchset adds x2apic write eoi msr notrace to avoid the debug codes 
splash and reverts irq_enter/irq_exit dance to avoid to make a very frequent 
interrupt slower because of debug code.

v5 -> v6:
 * split the patch 
 * don't duplicate the inline asm

v4 -> v5:
 * add notrace mark 

v3 -> v4: 
 * add notrace mark 

v2 -> v3:
 * revert irq_enter/irq_exit() since it is merged

v1 -> v2:
 * add write msr notrace to avoid debug codes splash instead of slowdown 
   a very frequent interrupt


Wanpeng Li (2):
  x86/msr: Add write msr notrace
  x86/apic: x2apic write eoi msr notrace

 arch/x86/include/asm/apic.h |  3 ++-
 arch/x86/include/asm/msr.h  | 14 +++++++++++++-
 arch/x86/kernel/apic/apic.c |  1 +
 arch/x86/kernel/kvm.c       |  4 ++--
 arch/x86/kernel/smp.c       |  2 --
 5 files changed, 18 insertions(+), 6 deletions(-)

-- 
1.9.1

[PATCH v6 1/2] x86/msr: Add write msr notrace

[Wanpeng Li]

From: Wanpeng Li <wanpeng.li@hotmail.com>

Add write msr notrace, it will be used by later patch.

Suggested-by: Peter Zijlstra <peterz@infradead.org>
Suggested-by: Paolo Bonzini <pbonzini@redhat.com>
Cc: Ingo Molnar <mingo@kernel.org>
Cc: Mike Galbraith <efault@gmx.de>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Paolo Bonzini <pbonzini@redhat.com>
Cc: Borislav Petkov <bp@alien8.de>
Signed-off-by: Wanpeng Li <wanpeng.li@hotmail.com>
---
 arch/x86/include/asm/msr.h | 14 +++++++++++++-
 1 file changed, 13 insertions(+), 1 deletion(-)

diff --git a/arch/x86/include/asm/msr.h b/arch/x86/include/asm/msr.h
index b5fee97..eec29a7 100644
--- a/arch/x86/include/asm/msr.h
+++ b/arch/x86/include/asm/msr.h
@@ -115,17 +115,29 @@ static inline unsigned long long native_read_msr_safe(unsigned int msr,
 }
 
 /* Can be uninlined because referenced by paravirt */
-notrace static inline void native_write_msr(unsigned int msr,
+notrace static inline void __native_write_msr_notrace(unsigned int msr,
 					    unsigned low, unsigned high)
 {
 	asm volatile("1: wrmsr\n"
 		     "2:\n"
 		     _ASM_EXTABLE_HANDLE(1b, 2b, ex_handler_wrmsr_unsafe)
 		     : : "c" (msr), "a"(low), "d" (high) : "memory");
+}
+
+/* Can be uninlined because referenced by paravirt */
+notrace static inline void native_write_msr(unsigned int msr,
+					    unsigned low, unsigned high)
+{
+	__native_write_msr_notrace(msr, low, high);
 	if (msr_tracepoint_active(__tracepoint_write_msr))
 		do_trace_write_msr(msr, ((u64)high << 32 | low), 0);
 }
 
+static inline void wrmsr_notrace(unsigned msr, unsigned low, unsigned high)
+{
+	__native_write_msr_notrace(msr, low, high);
+}
+
 /* Can be uninlined because referenced by paravirt */
 notrace static inline int native_write_msr_safe(unsigned int msr,
 					unsigned low, unsigned high)
-- 
1.9.1

Re: [PATCH v6 1/2] x86/msr: Add write msr notrace

[Borislav Petkov]

On Thu, Oct 27, 2016 at 12:38:41PM +0800, Wanpeng Li wrote:
> From: Wanpeng Li <wanpeng.li@hotmail.com>
> 
> Add write msr notrace, it will be used by later patch.
> 
> Suggested-by: Peter Zijlstra <peterz@infradead.org>
> Suggested-by: Paolo Bonzini <pbonzini@redhat.com>
> Cc: Ingo Molnar <mingo@kernel.org>
> Cc: Mike Galbraith <efault@gmx.de>
> Cc: Peter Zijlstra <peterz@infradead.org>
> Cc: Thomas Gleixner <tglx@linutronix.de>
> Cc: Paolo Bonzini <pbonzini@redhat.com>
> Cc: Borislav Petkov <bp@alien8.de>
> Signed-off-by: Wanpeng Li <wanpeng.li@hotmail.com>
> ---
>  arch/x86/include/asm/msr.h | 14 +++++++++++++-
>  1 file changed, 13 insertions(+), 1 deletion(-)
> 
> diff --git a/arch/x86/include/asm/msr.h b/arch/x86/include/asm/msr.h
> index b5fee97..eec29a7 100644
> --- a/arch/x86/include/asm/msr.h
> +++ b/arch/x86/include/asm/msr.h
> @@ -115,17 +115,29 @@ static inline unsigned long long native_read_msr_safe(unsigned int msr,
>  }
>  
>  /* Can be uninlined because referenced by paravirt */
> -notrace static inline void native_write_msr(unsigned int msr,
> +notrace static inline void __native_write_msr_notrace(unsigned int msr,
>  					    unsigned low, unsigned high)
					    ^^^^^^^
Align arguments on an opening brace.

Also, please fix that in a patch ontop of this one:

WARNING: storage class should be at the beginning of the declaration
#43: FILE: arch/x86/include/asm/msr.h:118:
+notrace static inline void __native_write_msr_notrace(unsigned int msr,

WARNING: Prefer 'unsigned int' to bare use of 'unsigned'
#54: FILE: arch/x86/include/asm/msr.h:129:
+                                           unsigned low, unsigned high)

And because we know what those are, you can convert them directly to u32.

IOW, the end result should be something like this:

static inline void notrace
__native_write_msr_notrace(unsigned int msr, u32 low, u32 high)

And yes, I suggested using the "_notrace" suffix for the name but then
it would look funny if we end up using it in code.

So maybe we should make that lower-level helper simply:

static inline void notrace
__native_write_msr(unsigned int msr, u32 low, u32 high)

to denote that it does purely the WRMSR operation and nothing else.

Yap, that looks the cleanest to me.

Thanks.

-- 
Regards/Gruss,
    Boris.

ECO tip #101: Trim your mails when you reply.

Re: [PATCH v6 1/2] x86/msr: Add write msr notrace

[Wanpeng Li]

2016-10-29 0:47 GMT+08:00 Borislav Petkov <bp@alien8.de>:
[...]
>>
>>  /* Can be uninlined because referenced by paravirt */
>> -notrace static inline void native_write_msr(unsigned int msr,
>> +notrace static inline void __native_write_msr_notrace(unsigned int msr,
>>                                           unsigned low, unsigned high)
>                                             ^^^^^^^
> Align arguments on an opening brace.

Other functions like native_write_msr() and native_write_msr_safe()
etc are also not aligned, so your suggestion maybe result in
inconsistent.

>
> Also, please fix that in a patch ontop of this one:
>
> WARNING: storage class should be at the beginning of the declaration
> #43: FILE: arch/x86/include/asm/msr.h:118:
> +notrace static inline void __native_write_msr_notrace(unsigned int msr,
>
> WARNING: Prefer 'unsigned int' to bare use of 'unsigned'
> #54: FILE: arch/x86/include/asm/msr.h:129:
> +                                           unsigned low, unsigned high)
>
> And because we know what those are, you can convert them directly to u32.

Ditto.

>
> IOW, the end result should be something like this:
>
> static inline void notrace
> __native_write_msr_notrace(unsigned int msr, u32 low, u32 high)
>
> And yes, I suggested using the "_notrace" suffix for the name but then
> it would look funny if we end up using it in code.
>
> So maybe we should make that lower-level helper simply:
>
> static inline void notrace
> __native_write_msr(unsigned int msr, u32 low, u32 high)
>
> to denote that it does purely the WRMSR operation and nothing else.
>
> Yap, that looks the cleanest to me.

Agreed.

Regards,
Wanpeng Li

Re: [PATCH v6 1/2] x86/msr: Add write msr notrace

[Borislav Petkov]

On Mon, Oct 31, 2016 at 07:30:33AM +0800, Wanpeng Li wrote:
> Other functions like native_write_msr() and native_write_msr_safe()
> etc are also not aligned, so your suggestion maybe result in
> inconsistent.

So align them too, while you're at it.

> > And because we know what those are, you can convert them directly to u32.
> 
> Ditto.

You could convert the rest to u32/u64 in another patch, ontop or if you
don't feel like it, I can take care of it.

Thanks.

-- 
Regards/Gruss,
    Boris.

ECO tip #101: Trim your mails when you reply.

Re: [PATCH v6 1/2] x86/msr: Add write msr notrace

[Wanpeng Li]

2016-10-31 7:46 GMT+08:00 Borislav Petkov <bp@alien8.de>:
> On Mon, Oct 31, 2016 at 07:30:33AM +0800, Wanpeng Li wrote:
>> Other functions like native_write_msr() and native_write_msr_safe()
>> etc are also not aligned, so your suggestion maybe result in
>> inconsistent.
>
> So align them too, while you're at it.
>
>> > And because we know what those are, you can convert them directly to u32.
>>
>> Ditto.
>
> You could convert the rest to u32/u64 in another patch, ontop or if you
> don't feel like it, I can take care of it.

I just fix my own "storage class should be at the beginning of the
declaration" coding style issue. Please feel free to handle align/u32
issues which existing before the patchset if you like. :)

Regards,
Wanpeng Li

[PATCH v6 2/2] x86/apic: x2apic write eoi msr notrace

[Wanpeng Li]

From: Wanpeng Li <wanpeng.li@hotmail.com>

| RCU used illegally from idle CPU!
| rcu_scheduler_active = 1, debug_locks = 0
| RCU used illegally from extended quiescent state!
| no locks held by swapper/1/0.
| 
|  [<ffffffff9d492b95>] do_trace_write_msr+0x135/0x140
|  [<ffffffff9d06f860>] native_write_msr+0x20/0x30
|  [<ffffffff9d065fad>] native_apic_msr_eoi_write+0x1d/0x30
|  [<ffffffff9d05bd1d>] smp_reschedule_interrupt+0x1d/0x30
|  [<ffffffff9d8daec6>] reschedule_interrupt+0x96/0xa0

Reschedule interrupt may be called in cpu idle state. This causes lockdep
check warning above.

As Peterz pointed out:

| So now we're making a very frequent interrupt slower because of debug 
| code.
|
| The thing is, many many smp_reschedule_interrupt() invocations don't
| actually execute anything much at all and are only send to tickle the
| return to user path (which does the actual preemption).
| 
| Having to do the whole irq_enter/irq_exit dance just for this unlikely
| debug case totally blows.

This patch converts x2apic write eoi msr to notrace to avoid the debug 
codes splash and reverts irq_enter/irq_exit dance to avoid to make a very 
frequent interrupt slower because of debug code.

Suggested-by: Peter Zijlstra <peterz@infradead.org>
Suggested-by: Paolo Bonzini <pbonzini@redhat.com>
Cc: Ingo Molnar <mingo@kernel.org>
Cc: Mike Galbraith <efault@gmx.de>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Paolo Bonzini <pbonzini@redhat.com>
Cc: Borislav Petkov <bp@alien8.de>
Signed-off-by: Wanpeng Li <wanpeng.li@hotmail.com>
---
 arch/x86/include/asm/apic.h | 3 ++-
 arch/x86/kernel/apic/apic.c | 1 +
 arch/x86/kernel/kvm.c       | 4 ++--
 arch/x86/kernel/smp.c       | 2 --
 4 files changed, 5 insertions(+), 5 deletions(-)

diff --git a/arch/x86/include/asm/apic.h b/arch/x86/include/asm/apic.h
index f5aaf6c..a5a0bcf 100644
--- a/arch/x86/include/asm/apic.h
+++ b/arch/x86/include/asm/apic.h
@@ -196,7 +196,7 @@ static inline void native_apic_msr_write(u32 reg, u32 v)
 
 static inline void native_apic_msr_eoi_write(u32 reg, u32 v)
 {
-	wrmsr(APIC_BASE_MSR + (APIC_EOI >> 4), APIC_EOI_ACK, 0);
+	wrmsr_notrace(APIC_BASE_MSR + (APIC_EOI >> 4), APIC_EOI_ACK, 0);
 }
 
 static inline u32 native_apic_msr_read(u32 reg)
@@ -332,6 +332,7 @@ struct apic {
 	 * on write for EOI.
 	 */
 	void (*eoi_write)(u32 reg, u32 v);
+	void (*native_eoi_write)(u32 reg, u32 v);
 	u64 (*icr_read)(void);
 	void (*icr_write)(u32 low, u32 high);
 	void (*wait_icr_idle)(void);
diff --git a/arch/x86/kernel/apic/apic.c b/arch/x86/kernel/apic/apic.c
index 88c657b..2686894 100644
--- a/arch/x86/kernel/apic/apic.c
+++ b/arch/x86/kernel/apic/apic.c
@@ -2263,6 +2263,7 @@ void __init apic_set_eoi_write(void (*eoi_write)(u32 reg, u32 v))
 	for (drv = __apicdrivers; drv < __apicdrivers_end; drv++) {
 		/* Should happen once for each apic */
 		WARN_ON((*drv)->eoi_write == eoi_write);
+		(*drv)->native_eoi_write = (*drv)->eoi_write;
 		(*drv)->eoi_write = eoi_write;
 	}
 }
diff --git a/arch/x86/kernel/kvm.c b/arch/x86/kernel/kvm.c
index edbbfc8..d230513 100644
--- a/arch/x86/kernel/kvm.c
+++ b/arch/x86/kernel/kvm.c
@@ -308,7 +308,7 @@ static void kvm_register_steal_time(void)
 
 static DEFINE_PER_CPU(unsigned long, kvm_apic_eoi) = KVM_PV_EOI_DISABLED;
 
-static void kvm_guest_apic_eoi_write(u32 reg, u32 val)
+notrace static void kvm_guest_apic_eoi_write(u32 reg, u32 val)
 {
 	/**
 	 * This relies on __test_and_clear_bit to modify the memory
@@ -319,7 +319,7 @@ static void kvm_guest_apic_eoi_write(u32 reg, u32 val)
 	 */
 	if (__test_and_clear_bit(KVM_PV_EOI_BIT, this_cpu_ptr(&kvm_apic_eoi)))
 		return;
-	apic_write(APIC_EOI, APIC_EOI_ACK);
+	apic->native_eoi_write(APIC_EOI, APIC_EOI_ACK);
 }
 
 static void kvm_guest_cpu_init(void)
diff --git a/arch/x86/kernel/smp.c b/arch/x86/kernel/smp.c
index c00cb64..68f8cc2 100644
--- a/arch/x86/kernel/smp.c
+++ b/arch/x86/kernel/smp.c
@@ -261,10 +261,8 @@ static inline void __smp_reschedule_interrupt(void)
 
 __visible void smp_reschedule_interrupt(struct pt_regs *regs)
 {
-	irq_enter();
 	ack_APIC_irq();
 	__smp_reschedule_interrupt();
-	irq_exit();
 	/*
 	 * KVM uses this interrupt to force a cpu out of guest mode
 	 */
-- 
1.9.1

Re: [PATCH v6 2/2] x86/apic: x2apic write eoi msr notrace

[Borislav Petkov]

On Thu, Oct 27, 2016 at 12:38:42PM +0800, Wanpeng Li wrote:

...

> This patch converts x2apic write eoi msr to notrace to avoid the debug 
> codes splash and reverts irq_enter/irq_exit dance to avoid to make a very 
> frequent interrupt slower because of debug code.
> 
> Suggested-by: Peter Zijlstra <peterz@infradead.org>
> Suggested-by: Paolo Bonzini <pbonzini@redhat.com>
> Cc: Ingo Molnar <mingo@kernel.org>
> Cc: Mike Galbraith <efault@gmx.de>
> Cc: Peter Zijlstra <peterz@infradead.org>
> Cc: Thomas Gleixner <tglx@linutronix.de>
> Cc: Paolo Bonzini <pbonzini@redhat.com>
> Cc: Borislav Petkov <bp@alien8.de>
> Signed-off-by: Wanpeng Li <wanpeng.li@hotmail.com>
> ---

...

> diff --git a/arch/x86/kernel/kvm.c b/arch/x86/kernel/kvm.c
> index edbbfc8..d230513 100644
> --- a/arch/x86/kernel/kvm.c
> +++ b/arch/x86/kernel/kvm.c
> @@ -308,7 +308,7 @@ static void kvm_register_steal_time(void)
>  
>  static DEFINE_PER_CPU(unsigned long, kvm_apic_eoi) = KVM_PV_EOI_DISABLED;
>  
> -static void kvm_guest_apic_eoi_write(u32 reg, u32 val)
> +notrace static void kvm_guest_apic_eoi_write(u32 reg, u32 val)

WARNING: storage class should be at the beginning of the declaration
#107: FILE: arch/x86/kernel/kvm.c:311:
+notrace static void kvm_guest_apic_eoi_write(u32 reg, u32 val)

Make sure you integrate checkpatch.pl in your patches creating workflow...

-- 
Regards/Gruss,
    Boris.

ECO tip #101: Trim your mails when you reply.