Re: [PATCH v2 1/4] KVM: add spinlock optimization framework

[Longpeng (Mike)]

On 2017/8/8 17:00, Paolo Bonzini wrote:

> On 08/08/2017 10:42, David Hildenbrand wrote:
>>
>>> +bool kvm_arch_vcpu_in_kernel(struct kvm_vcpu *vcpu)
>>> +{
>>> +	return false;
>>> +}
>>
>> why don't we need an EXPORT_SYMBOL here?
> 
> Is it used outside the KVM module?  I think no architecture actually needs
> to export it.
> 


Hi Paolo & David,

In my original approach, I call kvm_arch_vcpu_in_kernel() in handle_pause(),
without EXPORT_SYMBOL the compiler reports:
 ERROR: "kvm_arch_vcpu_in_kernel" [arch/x86/kvm/kvm-intel.ko] undefined!
 ERROR: "kvm_arch_vcpu_in_kernel" [arch/x86/kvm/kvm-amd.ko] undefined!

But Paolo's approach is significantly better, it's a work of art, thanks a lot.

-- 
Regards,
Longpeng(Mike)

>>> -void kvm_vcpu_on_spin(struct kvm_vcpu *me)
>>> +void kvm_vcpu_on_spin(struct kvm_vcpu *me, bool me_in_kern)
>>>  {
>>>  	struct kvm *kvm = me->kvm;
>>>  	struct kvm_vcpu *vcpu;
>>> @@ -2348,6 +2348,8 @@ void kvm_vcpu_on_spin(struct kvm_vcpu *me)
>>>  				continue;
>>>  			if (swait_active(&vcpu->wq) && !kvm_arch_vcpu_runnable(vcpu))
>>>  				continue;
>>> +			if (me_in_kern && !kvm_arch_vcpu_in_kernel(vcpu))
>>> +				continue;
>>
>>
>> hm, does this patch compile? (me_in_kern)
> 
> Why not? :)  This is what I have:
> 
>>From d62a40d49f44ff7e789a15416316ef1cba93fa85 Mon Sep 17 00:00:00 2001
> From: "Longpeng(Mike)" <longpeng2@xxxxxxxxxx>
> Date: Tue, 8 Aug 2017 12:05:32 +0800
> Subject: [PATCH 1/4] KVM: add spinlock optimization framework
> 
> If a vcpu exits due to request a user mode spinlock, then
> the spinlock-holder may be preempted in user mode or kernel mode.
> (Note that not all architectures trap spin loops in user mode,
> only AMD x86 and ARM/ARM64 currently do).
> 
> But if a vcpu exits in kernel mode, then the holder must be
> preempted in kernel mode, so we should choose a vcpu in kernel mode
> as a more likely candidate for the lock holder.
> 
> This introduces kvm_arch_vcpu_in_kernel() to decide whether the
> vcpu is in kernel-mode when it's preempted.  kvm_vcpu_on_spin's
> new argument says the same of the spinning VCPU.
> 
> Signed-off-by: Longpeng(Mike) <longpeng2@xxxxxxxxxx>
> Signed-off-by: Paolo Bonzini <pbonzini@xxxxxxxxxx>
> ---
>  arch/arm/kvm/handle_exit.c   | 2 +-
>  arch/arm64/kvm/handle_exit.c | 2 +-
>  arch/mips/kvm/mips.c         | 5 +++++
>  arch/powerpc/kvm/powerpc.c   | 5 +++++
>  arch/s390/kvm/diag.c         | 2 +-
>  arch/s390/kvm/kvm-s390.c     | 5 +++++
>  arch/x86/kvm/hyperv.c        | 2 +-
>  arch/x86/kvm/svm.c           | 2 +-
>  arch/x86/kvm/vmx.c           | 2 +-
>  arch/x86/kvm/x86.c           | 5 +++++
>  include/linux/kvm_host.h     | 3 ++-
>  virt/kvm/arm/arm.c           | 5 +++++
>  virt/kvm/kvm_main.c          | 4 +++-
>  13 files changed, 36 insertions(+), 8 deletions(-)
> 
> diff --git a/arch/arm/kvm/handle_exit.c b/arch/arm/kvm/handle_exit.c
> index 54442e375354..196122bb6968 100644
> --- a/arch/arm/kvm/handle_exit.c
> +++ b/arch/arm/kvm/handle_exit.c
> @@ -67,7 +67,7 @@ static int kvm_handle_wfx(struct kvm_vcpu *vcpu, struct kvm_run *run)
>  	if (kvm_vcpu_get_hsr(vcpu) & HSR_WFI_IS_WFE) {
>  		trace_kvm_wfx(*vcpu_pc(vcpu), true);
>  		vcpu->stat.wfe_exit_stat++;
> -		kvm_vcpu_on_spin(vcpu);
> +		kvm_vcpu_on_spin(vcpu, false);
>  	} else {
>  		trace_kvm_wfx(*vcpu_pc(vcpu), false);
>  		vcpu->stat.wfi_exit_stat++;
> diff --git a/arch/arm64/kvm/handle_exit.c b/arch/arm64/kvm/handle_exit.c
> index 17d8a1677a0b..da57622cacca 100644
> --- a/arch/arm64/kvm/handle_exit.c
> +++ b/arch/arm64/kvm/handle_exit.c
> @@ -84,7 +84,7 @@ static int kvm_handle_wfx(struct kvm_vcpu *vcpu, struct kvm_run *run)
>  	if (kvm_vcpu_get_hsr(vcpu) & ESR_ELx_WFx_ISS_WFE) {
>  		trace_kvm_wfx_arm64(*vcpu_pc(vcpu), true);
>  		vcpu->stat.wfe_exit_stat++;
> -		kvm_vcpu_on_spin(vcpu);
> +		kvm_vcpu_on_spin(vcpu, false);
>  	} else {
>  		trace_kvm_wfx_arm64(*vcpu_pc(vcpu), false);
>  		vcpu->stat.wfi_exit_stat++;
> diff --git a/arch/mips/kvm/mips.c b/arch/mips/kvm/mips.c
> index d4b2ad18eef2..70208bed5a15 100644
> --- a/arch/mips/kvm/mips.c
> +++ b/arch/mips/kvm/mips.c
> @@ -98,6 +98,11 @@ int kvm_arch_vcpu_runnable(struct kvm_vcpu *vcpu)
>  	return !!(vcpu->arch.pending_exceptions);
>  }
>  
> +bool kvm_arch_vcpu_in_kernel(struct kvm_vcpu *vcpu)
> +{
> +	return false;
> +}
> +
>  int kvm_arch_vcpu_should_kick(struct kvm_vcpu *vcpu)
>  {
>  	return 1;
>  }
> diff --git a/arch/powerpc/kvm/powerpc.c b/arch/powerpc/kvm/powerpc.c
> index 1a75c0b5f4ca..6184c45015f3 100644
> --- a/arch/powerpc/kvm/powerpc.c
> +++ b/arch/powerpc/kvm/powerpc.c
> @@ -58,6 +58,11 @@ int kvm_arch_vcpu_runnable(struct kvm_vcpu *v)
>  	return !!(v->arch.pending_exceptions) || kvm_request_pending(v);
>  }
>  
> +bool kvm_arch_vcpu_in_kernel(struct kvm_vcpu *vcpu)
> +{
> +	return false;
> +}
> +
>  int kvm_arch_vcpu_should_kick(struct kvm_vcpu *vcpu)
>  {
>  	return 1;
> diff --git a/arch/s390/kvm/diag.c b/arch/s390/kvm/diag.c
> index ce865bd4f81d..6182edebea3d 100644
> --- a/arch/s390/kvm/diag.c
> +++ b/arch/s390/kvm/diag.c
> @@ -150,7 +150,7 @@ static int __diag_time_slice_end(struct kvm_vcpu *vcpu)
>  {
>  	VCPU_EVENT(vcpu, 5, "%s", "diag time slice end");
>  	vcpu->stat.diagnose_44++;
> -	kvm_vcpu_on_spin(vcpu);
> +	kvm_vcpu_on_spin(vcpu, false);
>  	return 0;
>  }
>  
> diff --git a/arch/s390/kvm/kvm-s390.c b/arch/s390/kvm/kvm-s390.c
> index af09d3437631..0b0c689f1d9a 100644
> --- a/arch/s390/kvm/kvm-s390.c
> +++ b/arch/s390/kvm/kvm-s390.c
> @@ -2447,6 +2447,11 @@ int kvm_arch_vcpu_runnable(struct kvm_vcpu *vcpu)
>  	return kvm_s390_vcpu_has_irq(vcpu, 0);
>  }
>  
> +bool kvm_arch_vcpu_in_kernel(struct kvm_vcpu *vcpu)
> +{
> +	return false;
> +}
> +
>  void kvm_s390_vcpu_block(struct kvm_vcpu *vcpu)
>  {
>  	atomic_or(PROG_BLOCK_SIE, &vcpu->arch.sie_block->prog20);
> diff --git a/arch/x86/kvm/hyperv.c b/arch/x86/kvm/hyperv.c
> index bf9992300efa..5243d54f73ab 100644
> --- a/arch/x86/kvm/hyperv.c
> +++ b/arch/x86/kvm/hyperv.c
> @@ -1274,7 +1274,7 @@ int kvm_hv_hypercall(struct kvm_vcpu *vcpu)
>  
>  	switch (code) {
>  	case HVCALL_NOTIFY_LONG_SPIN_WAIT:
> -		kvm_vcpu_on_spin(vcpu);
> +		kvm_vcpu_on_spin(vcpu, false);
>  		break;
>  	case HVCALL_POST_MESSAGE:
>  	case HVCALL_SIGNAL_EVENT:
> diff --git a/arch/x86/kvm/svm.c b/arch/x86/kvm/svm.c
> index 2432bb952a30..0cc486fd9871 100644
> --- a/arch/x86/kvm/svm.c
> +++ b/arch/x86/kvm/svm.c
> @@ -3749,7 +3749,7 @@ static int interrupt_window_interception(struct vcpu_svm *svm)
>  
>  static int pause_interception(struct vcpu_svm *svm)
>  {
> -	kvm_vcpu_on_spin(&(svm->vcpu));
> +	kvm_vcpu_on_spin(&svm->vcpu, false);
>  	return 1;
>  }
>  
> diff --git a/arch/x86/kvm/vmx.c b/arch/x86/kvm/vmx.c
> index 2c0f5287fb78..fef784c22190 100644
> --- a/arch/x86/kvm/vmx.c
> +++ b/arch/x86/kvm/vmx.c
> @@ -6781,7 +6781,7 @@ static int handle_pause(struct kvm_vcpu *vcpu)
>  	if (ple_gap)
>  		grow_ple_window(vcpu);
>  
> -	kvm_vcpu_on_spin(vcpu);
> +	kvm_vcpu_on_spin(vcpu, false);
>  	return kvm_skip_emulated_instruction(vcpu);
>  }
>  
> diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
> index 33fd6b6419ef..aba9d038d09e 100644
> --- a/arch/x86/kvm/x86.c
> +++ b/arch/x86/kvm/x86.c
> @@ -8432,6 +8432,11 @@ int kvm_arch_vcpu_runnable(struct kvm_vcpu *vcpu)
>  	return kvm_vcpu_running(vcpu) || kvm_vcpu_has_events(vcpu);
>  }
>  
> +bool kvm_arch_vcpu_in_kernel(struct kvm_vcpu *vcpu)
> +{
> +	return false;
> +}
> +
>  int kvm_arch_vcpu_should_kick(struct kvm_vcpu *vcpu)
>  {
>  	return kvm_vcpu_exiting_guest_mode(vcpu) == IN_GUEST_MODE;
> diff --git a/include/linux/kvm_host.h b/include/linux/kvm_host.h
> index 28112d7917c1..6882538eda32 100644
> --- a/include/linux/kvm_host.h
> +++ b/include/linux/kvm_host.h
> @@ -720,7 +720,7 @@ int kvm_vcpu_write_guest(struct kvm_vcpu *vcpu, gpa_t gpa, const void *data,
>  bool kvm_vcpu_wake_up(struct kvm_vcpu *vcpu);
>  void kvm_vcpu_kick(struct kvm_vcpu *vcpu);
>  int kvm_vcpu_yield_to(struct kvm_vcpu *target);
> -void kvm_vcpu_on_spin(struct kvm_vcpu *vcpu);
> +void kvm_vcpu_on_spin(struct kvm_vcpu *vcpu, bool usermode_vcpu_not_eligible);
>  void kvm_load_guest_fpu(struct kvm_vcpu *vcpu);
>  void kvm_put_guest_fpu(struct kvm_vcpu *vcpu);
>  
> @@ -800,6 +800,7 @@ int kvm_arch_vcpu_ioctl_set_guest_debug(struct kvm_vcpu *vcpu,
>  void kvm_arch_hardware_unsetup(void);
>  void kvm_arch_check_processor_compat(void *rtn);
>  int kvm_arch_vcpu_runnable(struct kvm_vcpu *vcpu);
> +bool kvm_arch_vcpu_in_kernel(struct kvm_vcpu *vcpu);
>  int kvm_arch_vcpu_should_kick(struct kvm_vcpu *vcpu);
>  
>  #ifndef __KVM_HAVE_ARCH_VM_ALLOC
> diff --git a/virt/kvm/arm/arm.c b/virt/kvm/arm/arm.c
> index a39a1e161e63..862f820d06d4 100644
> --- a/virt/kvm/arm/arm.c
> +++ b/virt/kvm/arm/arm.c
> @@ -416,6 +416,11 @@ int kvm_arch_vcpu_runnable(struct kvm_vcpu *v)
>  		&& !v->arch.power_off && !v->arch.pause);
>  }
>  
> +bool kvm_arch_vcpu_in_kernel(struct kvm_vcpu *vcpu)
> +{
> +	return false;
> +}
> +
>  /* Just ensure a guest exit from a particular CPU */
>  static void exit_vm_noop(void *info)
>  {
> diff --git a/virt/kvm/kvm_main.c b/virt/kvm/kvm_main.c
> index 15252d723b54..e17c40d986f3 100644
> --- a/virt/kvm/kvm_main.c
> +++ b/virt/kvm/kvm_main.c
> @@ -2317,7 +2317,7 @@ static bool kvm_vcpu_eligible_for_directed_yield(struct kvm_vcpu *vcpu)
>  #endif
>  }
>  
> -void kvm_vcpu_on_spin(struct kvm_vcpu *me)
> +void kvm_vcpu_on_spin(struct kvm_vcpu *me, bool yield_to_kernel_mode)
>  {
>  	struct kvm *kvm = me->kvm;
>  	struct kvm_vcpu *vcpu;
> @@ -2348,6 +2348,8 @@ void kvm_vcpu_on_spin(struct kvm_vcpu *me)
>  				continue;
>  			if (swait_active(&vcpu->wq) && !kvm_arch_vcpu_runnable(vcpu))
>  				continue;
> +			if (yield_to_kernel_mode && !kvm_arch_vcpu_in_kernel(vcpu))
> +				continue;
>  			if (!kvm_vcpu_eligible_for_directed_yield(vcpu))
>  				continue;
>  


-- 
Regards,
Longpeng(Mike)