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Date: Fri, 8 Mar 2024 12:06:17 +0800
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Subject: Re: [RESEND v3 1/3] KVM: setup empty irq routing when create vm
To: Yi Wang <up2wing@gmail.com>
References: <20240229065313.1871095-1-foxywang@tencent.com>
 <20240229065313.1871095-2-foxywang@tencent.com>
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From: "Yang, Weijiang" <weijiang.yang@intel.com>
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On 2/29/2024 2:53 PM, Yi Wang wrote:
> From: Yi Wang <foxywang@tencent.com>
>
> Add a new function to setup empty irq routing in kvm path, which
> can be invoded in non-architecture-specific functions. The difference
> compared to the kvm_setup_empty_irq_routing() is this function just
> alloc the empty irq routing and does not need synchronize srcu, as
> we will call it in kvm_create_vm().
>
> Using the new adding function, we can setup empty irq routing when
> kvm_create_vm(), so that x86 and s390 no longer need to set
> empty/dummy irq routing when creating an IRQCHIP 'cause it avoid
> an synchronize_srcu.
>
> Signed-off-by: Yi Wang <foxywang@tencent.com>
> ---
>   include/linux/kvm_host.h |  1 +
>   virt/kvm/irqchip.c       | 19 +++++++++++++++++++
>   virt/kvm/kvm_main.c      |  4 ++++
>   3 files changed, 24 insertions(+)
>
> diff --git a/include/linux/kvm_host.h b/include/linux/kvm_host.h
> index 4944136efaa2..e91525c0a4ea 100644
> --- a/include/linux/kvm_host.h
> +++ b/include/linux/kvm_host.h
> @@ -2000,6 +2000,7 @@ int kvm_set_irq_routing(struct kvm *kvm,
>   			const struct kvm_irq_routing_entry *entries,
>   			unsigned nr,
>   			unsigned flags);
> +int kvm_setup_empty_irq_routing_lockless(struct kvm *kvm);
>   int kvm_set_routing_entry(struct kvm *kvm,
>   			  struct kvm_kernel_irq_routing_entry *e,
>   			  const struct kvm_irq_routing_entry *ue);
> diff --git a/virt/kvm/irqchip.c b/virt/kvm/irqchip.c
> index 1e567d1f6d3d..90fc43bd0fe4 100644
> --- a/virt/kvm/irqchip.c
> +++ b/virt/kvm/irqchip.c
> @@ -237,3 +237,22 @@ int kvm_set_irq_routing(struct kvm *kvm,
>   
>   	return r;
>   }
> +
> +int kvm_setup_empty_irq_routing_lockless(struct kvm *kvm)
> +{
> +	struct kvm_irq_routing_table *new;
> +	u32 i, j;
> +
> +	new = kzalloc(struct_size(new, map, 1), GFP_KERNEL_ACCOUNT);
> +	if (!new)
> +		return -ENOMEM;
> +
> +	new->nr_rt_entries = 1;
> +	for (i = 0; i < KVM_NR_IRQCHIPS; i++)
> +		for (j = 0; j < KVM_IRQCHIP_NUM_PINS; j++)
> +			new->chip[i][j] = -1;

Maybe it looks nicer by:
size = sizeof(int) * KVM_NR_IRQCHIPS *KVM_IRQCHIP_NUM_PINS;
memset(new->chip, -1, size);

> +
> +	RCU_INIT_POINTER(kvm->irq_routing, new);
> +
> +	return 0;
> +}
> diff --git a/virt/kvm/kvm_main.c b/virt/kvm/kvm_main.c
> index 7db96875ac46..db1b13fc0502 100644
> --- a/virt/kvm/kvm_main.c
> +++ b/virt/kvm/kvm_main.c
> @@ -1242,6 +1242,10 @@ static struct kvm *kvm_create_vm(unsigned long type, const char *fdname)
>   	if (r)
>   		goto out_err;
>   
> +	r = kvm_setup_empty_irq_routing_lockless(kvm);
> +	if (r)
> +		goto out_err;
> +
>   	mutex_lock(&kvm_lock);
>   	list_add(&kvm->vm_list, &vm_list);
>   	mutex_unlock(&kvm_lock);