Re: [PATCH 3/3] KVM: x86: do not scan IRR twice on APICv vmentry

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On 28/09/2016 16:00, Michael S. Tsirkin wrote:
> On Tue, Sep 27, 2016 at 11:20:13PM +0200, Paolo Bonzini wrote:
>> diff --git a/arch/x86/kvm/lapic.c b/arch/x86/kvm/lapic.c
>> index be8b7ad56dd1..85b79b90e3d0 100644
>> --- a/arch/x86/kvm/lapic.c
>> +++ b/arch/x86/kvm/lapic.c
>> @@ -317,7 +317,7 @@ static int find_highest_vector(void *bitmap)
>>  	     vec >= 0; vec -= APIC_VECTORS_PER_REG) {
>>  		reg = bitmap + REG_POS(vec);
>>  		if (*reg)
>> -			return fls(*reg) - 1 + vec;
>> +			return __fls(*reg) + vec;
>>  	}
>>  
>>  	return -1;
> 
> We checked that *reg is != 0 so __fls is safe.
> It's a correct micro-optimization but why stick it in this patch?

Just because I'm using __fls below in __kvm_apic_update_irr.

Paolo

>> @@ -337,25 +337,32 @@ static u8 count_vectors(void *bitmap)
>>  	return count;
>>  }
>>  
>> -void __kvm_apic_update_irr(u32 *pir, void *regs)
>> +int __kvm_apic_update_irr(u32 *pir, void *regs)
>>  {
>> -	u32 i, pir_val;
>> +	u32 i, vec;
>> +	u32 pir_val, irr_val;
>> +	int max_irr = -1;
>>  
>> -	for (i = 0; i <= 7; i++) {
>> +	for (i = vec = 0; i <= 7; i++, vec += 32) {
>>  		pir_val = READ_ONCE(pir[i]);
>> +		irr_val = *((u32 *)(regs + APIC_IRR + i * 0x10));
>>  		if (pir_val) {
>> -			pir_val = xchg(&pir[i], 0);
>> -			*((u32 *)(regs + APIC_IRR + i * 0x10)) |= pir_val;
>> +			irr_val |= xchg(&pir[i], 0);
>> +			*((u32 *)(regs + APIC_IRR + i * 0x10)) = irr_val;
>>  		}
>> +		if (irr_val)
>> +			max_irr = __fls(irr_val) + vec;
>>  	}
>> +
>> +	return max_irr;
>>  }
>>  EXPORT_SYMBOL_GPL(__kvm_apic_update_irr);
>>  
>> -void kvm_apic_update_irr(struct kvm_vcpu *vcpu, u32 *pir)
>> +int kvm_apic_update_irr(struct kvm_vcpu *vcpu, u32 *pir)
>>  {
>>  	struct kvm_lapic *apic = vcpu->arch.apic;
>>  
>> -	__kvm_apic_update_irr(pir, apic->regs);
>> +	return __kvm_apic_update_irr(pir, apic->regs);
>>  }
>>  EXPORT_SYMBOL_GPL(kvm_apic_update_irr);
>>  
>> @@ -376,7 +383,7 @@ static inline int apic_find_highest_irr(struct kvm_lapic *apic)
>>  		return -1;
>>  
>>  	if (apic->vcpu->arch.apicv_active)
>> -		kvm_x86_ops->sync_pir_to_irr(apic->vcpu);
>> +		kvm_x86_ops->sync_pir_to_irr(apic->vcpu, false);
>>  	result = apic_search_irr(apic);
>>  	ASSERT(result == -1 || result >= 16);
>>  
>> diff --git a/arch/x86/kvm/lapic.h b/arch/x86/kvm/lapic.h
>> index f60d01c29d51..fc72828c3782 100644
>> --- a/arch/x86/kvm/lapic.h
>> +++ b/arch/x86/kvm/lapic.h
>> @@ -70,8 +70,8 @@ int kvm_lapic_reg_read(struct kvm_lapic *apic, u32 offset, int len,
>>  bool kvm_apic_match_dest(struct kvm_vcpu *vcpu, struct kvm_lapic *source,
>>  			   int short_hand, unsigned int dest, int dest_mode);
>>  
>> -void __kvm_apic_update_irr(u32 *pir, void *regs);
>> -void kvm_apic_update_irr(struct kvm_vcpu *vcpu, u32 *pir);
>> +int __kvm_apic_update_irr(u32 *pir, void *regs);
>> +int kvm_apic_update_irr(struct kvm_vcpu *vcpu, u32 *pir);
>>  int kvm_apic_set_irq(struct kvm_vcpu *vcpu, struct kvm_lapic_irq *irq,
>>  		     struct dest_map *dest_map);
>>  int kvm_apic_local_deliver(struct kvm_lapic *apic, int lvt_type);
>> diff --git a/arch/x86/kvm/svm.c b/arch/x86/kvm/svm.c
>> index 9b4221471e3d..60e53fa2b554 100644
>> --- a/arch/x86/kvm/svm.c
>> +++ b/arch/x86/kvm/svm.c
>> @@ -4383,7 +4383,7 @@ static void svm_load_eoi_exitmap(struct kvm_vcpu *vcpu, u64 *eoi_exit_bitmap)
>>  	return;
>>  }
>>  
>> -static void svm_sync_pir_to_irr(struct kvm_vcpu *vcpu)
>> +static void svm_sync_pir_to_irr(struct kvm_vcpu *vcpu, bool sync_rvi)
>>  {
>>  	return;
>>  }
>> diff --git a/arch/x86/kvm/vmx.c b/arch/x86/kvm/vmx.c
>> index 207b9aa32915..1edefab54d01 100644
>> --- a/arch/x86/kvm/vmx.c
>> +++ b/arch/x86/kvm/vmx.c
>> @@ -4852,17 +4852,6 @@ static void vmx_deliver_posted_interrupt(struct kvm_vcpu *vcpu, int vector)
>>  		kvm_vcpu_kick(vcpu);
>>  }
>>  
>> -static void vmx_sync_pir_to_irr(struct kvm_vcpu *vcpu)
>> -{
>> -	struct vcpu_vmx *vmx = to_vmx(vcpu);
>> -
>> -	if (!pi_test_on(&vmx->pi_desc) ||
>> -	    !pi_test_and_clear_on(&vmx->pi_desc))
>> -		return;
>> -
>> -	kvm_apic_update_irr(vcpu, vmx->pi_desc.pir);
>> -}
>> -
>>  /*
>>   * Set up the vmcs's constant host-state fields, i.e., host-state fields that
>>   * will not change in the lifetime of the guest.
>> @@ -8609,6 +8598,20 @@ static void vmx_hwapic_irr_update(struct kvm_vcpu *vcpu, int max_irr)
>>  	}
>>  }
>>  
>> +static void vmx_sync_pir_to_irr(struct kvm_vcpu *vcpu, bool sync_rvi)
>> +{
>> +	struct vcpu_vmx *vmx = to_vmx(vcpu);
>> +	int max_irr;
>> +
>> +	if (!pi_test_on(&vmx->pi_desc) ||
>> +	    !pi_test_and_clear_on(&vmx->pi_desc))
>> +		return;
>> +
>> +	max_irr = kvm_apic_update_irr(vcpu, vmx->pi_desc.pir);
>> +	if (sync_rvi)
>> +		vmx_hwapic_irr_update(vcpu, max_irr);
>> +}
>> +
>>  static void vmx_load_eoi_exitmap(struct kvm_vcpu *vcpu, u64 *eoi_exit_bitmap)
>>  {
>>  	if (!kvm_vcpu_apicv_active(vcpu))
>> diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
>> index 604cfbfc5bee..148e14fdc55d 100644
>> --- a/arch/x86/kvm/x86.c
>> +++ b/arch/x86/kvm/x86.c
>> @@ -2821,7 +2821,7 @@ static int kvm_vcpu_ioctl_get_lapic(struct kvm_vcpu *vcpu,
>>  				    struct kvm_lapic_state *s)
>>  {
>>  	if (vcpu->arch.apicv_active)
>> -		kvm_x86_ops->sync_pir_to_irr(vcpu);
>> +		kvm_x86_ops->sync_pir_to_irr(vcpu, false);
>>  
>>  	return kvm_apic_get_state(vcpu, s);
>>  }
>> @@ -6448,7 +6448,7 @@ static void vcpu_scan_ioapic(struct kvm_vcpu *vcpu)
>>  		kvm_scan_ioapic_routes(vcpu, vcpu->arch.ioapic_handled_vectors);
>>  	else {
>>  		if (vcpu->arch.apicv_active)
>> -			kvm_x86_ops->sync_pir_to_irr(vcpu);
>> +			kvm_x86_ops->sync_pir_to_irr(vcpu, false);
>>  		kvm_ioapic_scan_entry(vcpu, vcpu->arch.ioapic_handled_vectors);
>>  	}
>>  	bitmap_or((ulong *)eoi_exit_bitmap, vcpu->arch.ioapic_handled_vectors,
>> @@ -6611,8 +6611,7 @@ static int vcpu_enter_guest(struct kvm_vcpu *vcpu)
>>  		 * virtual interrupt delivery.
>>  		 */
>>  		if (vcpu->arch.apicv_active)
>> -			kvm_x86_ops->hwapic_irr_update(vcpu,
>> -				kvm_lapic_find_highest_irr(vcpu));
>> +			kvm_x86_ops->sync_pir_to_irr(vcpu, true);
>>  	}
>>  
>>  	if (kvm_check_request(KVM_REQ_EVENT, vcpu) || req_int_win) {
>> -- 
>> 1.8.3.1
> 
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