Re: [PATCH 4/9] KVM: arm/arm64: vgic: Get rid of unnecessary process_maintenance operation

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On 20/03/17 10:58, Christoffer Dall wrote:
> From: Christoffer Dall <christoffer.dall@xxxxxxxxxx>
> 
> Since we always read back the LRs that we wrote to the guest and the
> MISR and EISR registers simply provide a summary of the configuration of
> the bits in the LRs, there is really no need to read back those status
> registers and process them.  We can might as well just signal the
> notifyfd when folding the LR state and save some cycles in the process.
> 
> Signed-off-by: Christoffer Dall <christoffer.dall@xxxxxxxxxx>
> ---
>  virt/kvm/arm/vgic/vgic-v2.c | 55 ++++++++++-----------------------------------
>  virt/kvm/arm/vgic/vgic-v3.c | 47 +++++++++++---------------------------
>  virt/kvm/arm/vgic/vgic.c    |  8 +++----
>  virt/kvm/arm/vgic/vgic.h    |  4 ++--
>  4 files changed, 31 insertions(+), 83 deletions(-)
> 
> diff --git a/virt/kvm/arm/vgic/vgic-v2.c b/virt/kvm/arm/vgic/vgic-v2.c
> index dfe6e5e..0172754 100644
> --- a/virt/kvm/arm/vgic/vgic-v2.c
> +++ b/virt/kvm/arm/vgic/vgic-v2.c
> @@ -22,20 +22,6 @@
>  
>  #include "vgic.h"
>  
> -/*
> - * Call this function to convert a u64 value to an unsigned long * bitmask
> - * in a way that works on both 32-bit and 64-bit LE and BE platforms.
> - *
> - * Warning: Calling this function may modify *val.
> - */
> -static unsigned long *u64_to_bitmask(u64 *val)
> -{
> -#if defined(CONFIG_CPU_BIG_ENDIAN) && BITS_PER_LONG == 32
> -	*val = (*val >> 32) | (*val << 32);
> -#endif
> -	return (unsigned long *)val;
> -}
> -

Getting rid of u64_to_bitmask makes me feel slightly better...

>  static inline void vgic_v2_write_lr(int lr, u32 val)
>  {
>  	void __iomem *base = kvm_vgic_global_state.vctrl_base;
> @@ -51,38 +37,10 @@ void vgic_v2_init_lrs(void)
>  		vgic_v2_write_lr(i, 0);
>  }
>  
> -void vgic_v2_process_maintenance(struct kvm_vcpu *vcpu)
> +void vgic_v2_clear_uie(struct kvm_vcpu *vcpu)
>  {
>  	struct vgic_v2_cpu_if *cpuif = &vcpu->arch.vgic_cpu.vgic_v2;
> -
> -	if (cpuif->vgic_misr & GICH_MISR_EOI) {
> -		u64 eisr = cpuif->vgic_eisr;
> -		unsigned long *eisr_bmap = u64_to_bitmask(&eisr);
> -		int lr;
> -
> -		for_each_set_bit(lr, eisr_bmap, kvm_vgic_global_state.nr_lr) {
> -			u32 intid = cpuif->vgic_lr[lr] & GICH_LR_VIRTUALID;
> -
> -			WARN_ON(cpuif->vgic_lr[lr] & GICH_LR_STATE);
> -
> -			/* Only SPIs require notification */
> -			if (vgic_valid_spi(vcpu->kvm, intid))
> -				kvm_notify_acked_irq(vcpu->kvm, 0,
> -						     intid - VGIC_NR_PRIVATE_IRQS);
> -		}
> -	}
> -
> -	/* check and disable underflow maintenance IRQ */
>  	cpuif->vgic_hcr &= ~GICH_HCR_UIE;
> -
> -	/*
> -	 * In the next iterations of the vcpu loop, if we sync the
> -	 * vgic state after flushing it, but before entering the guest
> -	 * (this happens for pending signals and vmid rollovers), then
> -	 * make sure we don't pick up any old maintenance interrupts
> -	 * here.
> -	 */
> -	cpuif->vgic_eisr = 0;
>  }
>  
>  void vgic_v2_set_underflow(struct kvm_vcpu *vcpu)
> @@ -92,6 +50,12 @@ void vgic_v2_set_underflow(struct kvm_vcpu *vcpu)
>  	cpuif->vgic_hcr |= GICH_HCR_UIE;
>  }
>  
> +static bool lr_signals_eoi_mi(u32 lr_val)
> +{
> +	return !(lr_val & GICH_LR_STATE) && (lr_val & GICH_LR_EOI) &&
> +	       !(lr_val & GICH_LR_HW);
> +}
> +
>  /*
>   * transfer the content of the LRs back into the corresponding ap_list:
>   * - active bit is transferred as is
> @@ -109,6 +73,11 @@ void vgic_v2_fold_lr_state(struct kvm_vcpu *vcpu)
>  		u32 intid = val & GICH_LR_VIRTUALID;
>  		struct vgic_irq *irq;
>  
> +		/* Notify fds when the guest EOI'ed a level-triggered SPI */
> +		if (lr_signals_eoi_mi(val) && vgic_valid_spi(vcpu->kvm, intid))
> +			kvm_notify_acked_irq(vcpu->kvm, 0,
> +					     intid - VGIC_NR_PRIVATE_IRQS);
> +
>  		irq = vgic_get_irq(vcpu->kvm, vcpu, intid);
>  
>  		spin_lock(&irq->irq_lock);
> diff --git a/virt/kvm/arm/vgic/vgic-v3.c b/virt/kvm/arm/vgic/vgic-v3.c
> index 3d7796c..7880c5c 100644
> --- a/virt/kvm/arm/vgic/vgic-v3.c
> +++ b/virt/kvm/arm/vgic/vgic-v3.c
> @@ -21,42 +21,9 @@
>  
>  #include "vgic.h"
>  
> -void vgic_v3_process_maintenance(struct kvm_vcpu *vcpu)
> +void vgic_v3_clear_uie(struct kvm_vcpu *vcpu)
>  {
>  	struct vgic_v3_cpu_if *cpuif = &vcpu->arch.vgic_cpu.vgic_v3;
> -	u32 model = vcpu->kvm->arch.vgic.vgic_model;
> -
> -	if (cpuif->vgic_misr & ICH_MISR_EOI) {
> -		unsigned long eisr_bmap = cpuif->vgic_eisr;
> -		int lr;
> -
> -		for_each_set_bit(lr, &eisr_bmap, kvm_vgic_global_state.nr_lr) {
> -			u32 intid;
> -			u64 val = cpuif->vgic_lr[lr];
> -
> -			if (model == KVM_DEV_TYPE_ARM_VGIC_V3)
> -				intid = val & ICH_LR_VIRTUAL_ID_MASK;
> -			else
> -				intid = val & GICH_LR_VIRTUALID;
> -
> -			WARN_ON(cpuif->vgic_lr[lr] & ICH_LR_STATE);
> -
> -			/* Only SPIs require notification */
> -			if (vgic_valid_spi(vcpu->kvm, intid))
> -				kvm_notify_acked_irq(vcpu->kvm, 0,
> -						     intid - VGIC_NR_PRIVATE_IRQS);
> -		}
> -
> -		/*
> -		 * In the next iterations of the vcpu loop, if we sync
> -		 * the vgic state after flushing it, but before
> -		 * entering the guest (this happens for pending
> -		 * signals and vmid rollovers), then make sure we
> -		 * don't pick up any old maintenance interrupts here.
> -		 */
> -		cpuif->vgic_eisr = 0;
> -	}
> -
>  	cpuif->vgic_hcr &= ~ICH_HCR_UIE;
>  }
>  
> @@ -67,6 +34,12 @@ void vgic_v3_set_underflow(struct kvm_vcpu *vcpu)
>  	cpuif->vgic_hcr |= ICH_HCR_UIE;
>  }
>  
> +static bool lr_signals_eoi_mi(u64 lr_val)
> +{
> +	return !(lr_val & ICH_LR_STATE) && (lr_val & ICH_LR_EOI) &&
> +	       !(lr_val & ICH_LR_HW);
> +}
> +
>  void vgic_v3_fold_lr_state(struct kvm_vcpu *vcpu)
>  {
>  	struct vgic_v3_cpu_if *cpuif = &vcpu->arch.vgic_cpu.vgic_v3;
> @@ -82,6 +55,12 @@ void vgic_v3_fold_lr_state(struct kvm_vcpu *vcpu)
>  			intid = val & ICH_LR_VIRTUAL_ID_MASK;
>  		else
>  			intid = val & GICH_LR_VIRTUALID;
> +
> +		/* Notify fds when the guest EOI'ed a level-triggered IRQ */
> +		if (lr_signals_eoi_mi(val) && vgic_valid_spi(vcpu->kvm, intid))
> +			kvm_notify_acked_irq(vcpu->kvm, 0,
> +					     intid - VGIC_NR_PRIVATE_IRQS);
> +
>  		irq = vgic_get_irq(vcpu->kvm, vcpu, intid);
>  		if (!irq)	/* An LPI could have been unmapped. */
>  			continue;
> diff --git a/virt/kvm/arm/vgic/vgic.c b/virt/kvm/arm/vgic/vgic.c
> index 1436c2e..f5b3c25 100644
> --- a/virt/kvm/arm/vgic/vgic.c
> +++ b/virt/kvm/arm/vgic/vgic.c
> @@ -527,12 +527,12 @@ static void vgic_prune_ap_list(struct kvm_vcpu *vcpu)
>  	spin_unlock(&vgic_cpu->ap_list_lock);
>  }
>  
> -static inline void vgic_process_maintenance_interrupt(struct kvm_vcpu *vcpu)
> +static inline void vgic_clear_uie(struct kvm_vcpu *vcpu)
>  {
>  	if (kvm_vgic_global_state.type == VGIC_V2)
> -		vgic_v2_process_maintenance(vcpu);
> +		vgic_v2_clear_uie(vcpu);
>  	else
> -		vgic_v3_process_maintenance(vcpu);
> +		vgic_v3_clear_uie(vcpu);
>  }
>  
>  static inline void vgic_fold_lr_state(struct kvm_vcpu *vcpu)
> @@ -642,7 +642,7 @@ void kvm_vgic_sync_hwstate(struct kvm_vcpu *vcpu)
>  	if (unlikely(!vgic_initialized(vcpu->kvm)))
>  		return;
>  
> -	vgic_process_maintenance_interrupt(vcpu);
> +	vgic_clear_uie(vcpu);
>  	vgic_fold_lr_state(vcpu);

nit: If you moved vgic_*_clear_uie() into vgic_*_fold_lr_state, you
could get rid of this call, extra prototypes, and save yourself the
extra check. Not a big deal though.

>  	vgic_prune_ap_list(vcpu);
>  
> diff --git a/virt/kvm/arm/vgic/vgic.h b/virt/kvm/arm/vgic/vgic.h
> index 3f64220..72ba9ee 100644
> --- a/virt/kvm/arm/vgic/vgic.h
> +++ b/virt/kvm/arm/vgic/vgic.h
> @@ -112,7 +112,7 @@ void vgic_kick_vcpus(struct kvm *kvm);
>  int vgic_check_ioaddr(struct kvm *kvm, phys_addr_t *ioaddr,
>  		      phys_addr_t addr, phys_addr_t alignment);
>  
> -void vgic_v2_process_maintenance(struct kvm_vcpu *vcpu);
> +void vgic_v2_clear_uie(struct kvm_vcpu *vcpu);
>  void vgic_v2_fold_lr_state(struct kvm_vcpu *vcpu);
>  void vgic_v2_populate_lr(struct kvm_vcpu *vcpu, struct vgic_irq *irq, int lr);
>  void vgic_v2_clear_lr(struct kvm_vcpu *vcpu, int lr);
> @@ -143,7 +143,7 @@ static inline void vgic_get_irq_kref(struct vgic_irq *irq)
>  	kref_get(&irq->refcount);
>  }
>  
> -void vgic_v3_process_maintenance(struct kvm_vcpu *vcpu);
> +void vgic_v3_clear_uie(struct kvm_vcpu *vcpu);
>  void vgic_v3_fold_lr_state(struct kvm_vcpu *vcpu);
>  void vgic_v3_populate_lr(struct kvm_vcpu *vcpu, struct vgic_irq *irq, int lr);
>  void vgic_v3_clear_lr(struct kvm_vcpu *vcpu, int lr);
> 

Reviewed-by: Marc Zyngier <marc.zyngier@xxxxxxx>

Thanks,

	M.
-- 
Jazz is not dead. It just smells funny...



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