Re: [v5 1/3] KVM: setup empty irq routing when create vm

[Christian Borntraeger]

Am 06.05.24 um 12:17 schrieb Yi Wang:
> From: Yi Wang <foxywang@xxxxxxxxxxx>
>
> 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@xxxxxxxxxxx>
Acked-by: Christian Borntraeger <borntraeger@xxxxxxxxxxxxx>

> ---
>   include/linux/kvm_host.h |  2 ++
>   virt/kvm/irqchip.c       | 23 +++++++++++++++++++++++
>   virt/kvm/kvm_main.c      |  9 ++++++++-
>   3 files changed, 33 insertions(+), 1 deletion(-)
>
> diff --git a/include/linux/kvm_host.h b/include/linux/kvm_host.h
> index 48f31dcd318a..a5f12b667ca5 100644
> --- a/include/linux/kvm_host.h
> +++ b/include/linux/kvm_host.h
> @@ -2100,6 +2100,7 @@ int kvm_set_irq_routing(struct kvm *kvm,
>   			const struct kvm_irq_routing_entry *entries,
>   			unsigned nr,
>   			unsigned flags);
> +int kvm_init_irq_routing(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);
> @@ -2108,6 +2109,7 @@ void kvm_free_irq_routing(struct kvm *kvm);
>   #else
>   
>   static inline void kvm_free_irq_routing(struct kvm *kvm) {}
> +int kvm_init_irq_routing(struct kvm *kvm) {}
>   
>   #endif
>   
> diff --git a/virt/kvm/irqchip.c b/virt/kvm/irqchip.c
> index 1e567d1f6d3d..ec1fda7fffea 100644
> --- a/virt/kvm/irqchip.c
> +++ b/virt/kvm/irqchip.c
> @@ -237,3 +237,26 @@ int kvm_set_irq_routing(struct kvm *kvm,
>   
>   	return r;
>   }
> +
> +/*
> + * Alloc empty irq routing.
> + * Called only during vm creation, because we don't synchronize_srcu here.
> + */
> +int kvm_init_irq_routing(struct kvm *kvm)
> +{
> +	struct kvm_irq_routing_table *new;
> +	int chip_size;
> +
> +	new = kzalloc(struct_size(new, map, 1), GFP_KERNEL_ACCOUNT);
> +	if (!new)
> +		return -ENOMEM;
> +
> +	new->nr_rt_entries = 1;
> +
> +	chip_size = sizeof(int) * KVM_NR_IRQCHIPS * KVM_IRQCHIP_NUM_PINS;
> +	memset(new->chip, -1, chip_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 ff0a20565f90..4100ebdd14fe 100644
> --- a/virt/kvm/kvm_main.c
> +++ b/virt/kvm/kvm_main.c
> @@ -1233,6 +1233,11 @@ static struct kvm *kvm_create_vm(unsigned long type, const char *fdname)
>   		goto out_err_no_irq_srcu;
>   
>   	refcount_set(&kvm->users_count, 1);
> +
> +	r = kvm_init_irq_routing(kvm);
> +	if (r)
> +		goto out_err_no_irq_routing;
> +
>   	for (i = 0; i < kvm_arch_nr_memslot_as_ids(kvm); i++) {
>   		for (j = 0; j < 2; j++) {
>   			slots = &kvm->__memslots[i][j];
> @@ -1308,9 +1313,11 @@ static struct kvm *kvm_create_vm(unsigned long type, const char *fdname)
>   out_err_no_disable:
>   	kvm_arch_destroy_vm(kvm);
>   out_err_no_arch_destroy_vm:
> -	WARN_ON_ONCE(!refcount_dec_and_test(&kvm->users_count));
>   	for (i = 0; i < KVM_NR_BUSES; i++)
>   		kfree(kvm_get_bus(kvm, i));
> +	kvm_free_irq_routing(kvm);
> +out_err_no_irq_routing:
> +	WARN_ON_ONCE(!refcount_dec_and_test(&kvm->users_count));
>   	cleanup_srcu_struct(&kvm->irq_srcu);
>   out_err_no_irq_srcu:
>   	cleanup_srcu_struct(&kvm->srcu);