Subject: [PATCH v3 06/19] arm/arm64: KVM: move [sg]et_lr into per-VM ops

From: [email-masked] (Christoffer Dall)
Date: Mon, 3 Nov 2014 15:15:10 +0100

On Fri, Oct 31, 2014 at 05:26:41PM +0000, Andre Przywara wrote:
> The function to set the VGIC's list registers are not only dependent
> on the host GIC model, but need to behave slightly different for
> the type of emulated guest GIC.
> So move the functions into the new struct vgic_vm_ops and initialize
> them properly to prepare for guest GICv3 support later.
> 
> Signed-off-by: Andre Przywara <[email-masked]>
> ---
>  include/kvm/arm_vgic.h |    5 +++--
>  virt/kvm/arm/vgic-v2.c |   17 +++++++++++++++--
>  virt/kvm/arm/vgic-v3.c |   16 ++++++++++++++--
>  virt/kvm/arm/vgic.c    |    9 +++++++--
>  4 files changed, 39 insertions(+), 8 deletions(-)
> 
> diff --git a/include/kvm/arm_vgic.h b/include/kvm/arm_vgic.h
> index bfb660a..a6d41f1 100644
> --- a/include/kvm/arm_vgic.h
> +++ b/include/kvm/arm_vgic.h
> @@ -108,8 +108,6 @@ struct vgic_vmcr {
>  };
>  
>  struct vgic_ops {
> -	struct vgic_lr	(*get_lr)(const struct kvm_vcpu *, int);
> -	void	(*set_lr)(struct kvm_vcpu *, int, struct vgic_lr);
>  	void	(*sync_lr_elrsr)(struct kvm_vcpu *, int, struct vgic_lr);
>  	u64	(*get_elrsr)(const struct kvm_vcpu *vcpu);
>  	u64	(*get_eisr)(const struct kvm_vcpu *vcpu);
> @@ -132,9 +130,12 @@ struct vgic_params {
>  	unsigned int	maint_irq;
>  	/* Virtual control interface base address */
>  	void __iomem	*vctrl_base;
> +	bool (*init_emul)(struct kvm *kvm, int type);
>  };
>  
>  struct vgic_vm_ops {
> +	struct vgic_lr	(*get_lr)(const struct kvm_vcpu *, int);
> +	void	(*set_lr)(struct kvm_vcpu *, int, struct vgic_lr);
>  	bool	(*handle_mmio)(struct kvm_vcpu *, struct kvm_run *,
>  			       struct kvm_exit_mmio *);
>  	bool	(*queue_sgi)(struct kvm_vcpu *vcpu, int irq);

this has now become incredibly confusing, what are your thoughts on
renaming vgic_ops to kvm_gic_ops to make it clear that this structure is
about hardware-managing ops and vgic_vm_ops is about the vgic, the
virtual instance?

> diff --git a/virt/kvm/arm/vgic-v2.c b/virt/kvm/arm/vgic-v2.c
> index 2935405..bdc8d97 100644
> --- a/virt/kvm/arm/vgic-v2.c
> +++ b/virt/kvm/arm/vgic-v2.c
> @@ -143,8 +143,6 @@ static void vgic_v2_enable(struct kvm_vcpu *vcpu)
>  }
>  
>  static const struct vgic_ops vgic_v2_ops = {
> -	.get_lr			= vgic_v2_get_lr,
> -	.set_lr			= vgic_v2_set_lr,
>  	.sync_lr_elrsr		= vgic_v2_sync_lr_elrsr,
>  	.get_elrsr		= vgic_v2_get_elrsr,
>  	.get_eisr		= vgic_v2_get_eisr,
> @@ -158,6 +156,20 @@ static const struct vgic_ops vgic_v2_ops = {
>  
>  static struct vgic_params vgic_v2_params;
>  
> +static bool vgic_v2_init_emul(struct kvm *kvm, int type)
> +{
> +	struct vgic_vm_ops *vm_ops = &kvm->arch.vgic.vm_ops;
> +
> +	switch (type) {
> +	case KVM_DEV_TYPE_ARM_VGIC_V2:
> +		vm_ops->get_lr = vgic_v2_get_lr;
> +		vm_ops->set_lr = vgic_v2_set_lr;
> +		return true;
> +	}
> +
> +	return false;
> +}
> +
>  /**
>   * vgic_v2_probe - probe for a GICv2 compatible interrupt controller in DT
>   * @node:	pointer to the DT node
> @@ -196,6 +208,7 @@ int vgic_v2_probe(struct device_node *vgic_node,
>  		ret = -ENOMEM;
>  		goto out;
>  	}
> +	vgic->init_emul = vgic_v2_init_emul;
>  
>  	vgic->nr_lr = readl_relaxed(vgic->vctrl_base + GICH_VTR);
>  	vgic->nr_lr = (vgic->nr_lr & 0x3f) + 1;
> diff --git a/virt/kvm/arm/vgic-v3.c b/virt/kvm/arm/vgic-v3.c
> index 1c2c8ee..a38339e 100644
> --- a/virt/kvm/arm/vgic-v3.c
> +++ b/virt/kvm/arm/vgic-v3.c
> @@ -157,8 +157,6 @@ static void vgic_v3_enable(struct kvm_vcpu *vcpu)
>  }
>  
>  static const struct vgic_ops vgic_v3_ops = {
> -	.get_lr			= vgic_v3_get_lr,
> -	.set_lr			= vgic_v3_set_lr,
>  	.sync_lr_elrsr		= vgic_v3_sync_lr_elrsr,
>  	.get_elrsr		= vgic_v3_get_elrsr,
>  	.get_eisr		= vgic_v3_get_eisr,
> @@ -170,6 +168,19 @@ static const struct vgic_ops vgic_v3_ops = {
>  	.enable			= vgic_v3_enable,
>  };
>  
> +static bool vgic_v3_init_emul_compat(struct kvm *kvm, int type)
> +{
> +	struct vgic_vm_ops *vm_ops = &kvm->arch.vgic.vm_ops;
> +
> +	switch (type) {
> +	case KVM_DEV_TYPE_ARM_VGIC_V2:
> +		vm_ops->get_lr = vgic_v3_get_lr;
> +		vm_ops->set_lr = vgic_v3_set_lr;
> +		return true;
> +	}
> +	return false;
> +}
> +
>  static struct vgic_params vgic_v3_params;
>  
>  /**
> @@ -231,6 +242,7 @@ int vgic_v3_probe(struct device_node *vgic_node,
>  		goto out;
>  	}
>  
> +	vgic->init_emul = vgic_v3_init_emul_compat;
>  	vgic->vcpu_base = vcpu_res.start;
>  	vgic->vctrl_base = NULL;
>  	vgic->type = VGIC_V3;
> diff --git a/virt/kvm/arm/vgic.c b/virt/kvm/arm/vgic.c
> index 2c16684..8c2e707 100644
> --- a/virt/kvm/arm/vgic.c
> +++ b/virt/kvm/arm/vgic.c
> @@ -1278,13 +1278,13 @@ static void vgic_update_state(struct kvm *kvm)
>  
>  static struct vgic_lr vgic_get_lr(const struct kvm_vcpu *vcpu, int lr)
>  {
> -	return vgic_ops->get_lr(vcpu, lr);
> +	return vgic_vm_op(vcpu->kvm, get_lr)(vcpu, lr);
>  }
>  
>  static void vgic_set_lr(struct kvm_vcpu *vcpu, int lr,
>  			       struct vgic_lr vlr)
>  {
> -	vgic_ops->set_lr(vcpu, lr, vlr);
> +	return vgic_vm_op(vcpu->kvm, set_lr)(vcpu, lr, vlr);
>  }
>  
>  static void vgic_sync_lr_elrsr(struct kvm_vcpu *vcpu, int lr,
> @@ -2072,6 +2072,11 @@ int kvm_vgic_create(struct kvm *kvm, u32 type)
>  		}
>  	}
>  
> +	if (!vgic->init_emul(kvm, type)) {
> +		ret = -ENODEV;
> +		goto out_unlock;
> +	}
> +
>  	spin_lock_init(&kvm->arch.vgic.lock);
>  	kvm->arch.vgic.in_kernel = true;
>  	kvm->arch.vgic.vgic_model = type;
> -- 
> 1.7.9.5
> 

Thanks for splitting up the patches, it's certainly better to review.

However, my question from the last round still stands.  What you're
doing here is setting a sh*tload of function pointers through an amazing
amount of abstractions to avoid something like

void vgic_v2_set_lr(struct kvm_vgic *vgic)
{
	switch (vgic->type) {
	case KVM_DEV_TYPE_ARM_VGIC_V2:
		foo();
		break;
	case KVM_DEV_TYPE_ARM_VGIC_V3:
		bar();
		break;
	}
}

So I have to ask: What's the benefit? That you'll have fewer
conditionals?  But god have mercy on the poor people having to debug
some issue and figure out which function the code actually calls when it
(inside another complicated piece of logic) sets a LR.

This just feels like we're doing something incredibly wrong...

Thoughts?

-Christoffer