Re: [PATCH 1/5] KVM: Move wiping of the kvm->vcpus array to common code

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On Fri,  5 Nov 2021 19:20:57 +0000
Marc Zyngier <maz@xxxxxxxxxx> wrote:

> All architectures have similar loops iterating over the vcpus,
> freeing one vcpu at a time, and eventually wiping the reference
> off the vcpus array. They are also inconsistently taking
> the kvm->lock mutex when wiping the references from the array.
> 
> Make this code common, which will simplify further changes.
> 
> Signed-off-by: Marc Zyngier <maz@xxxxxxxxxx>

no objections

Reviewed-by: Claudio Imbrenda <imbrenda@xxxxxxxxxxxxx>

> ---
>  arch/arm64/kvm/arm.c       | 10 +---------
>  arch/mips/kvm/mips.c       | 21 +--------------------
>  arch/powerpc/kvm/powerpc.c | 10 +---------
>  arch/riscv/kvm/vm.c        | 10 +---------
>  arch/s390/kvm/kvm-s390.c   | 18 +-----------------
>  arch/x86/kvm/x86.c         |  9 +--------
>  include/linux/kvm_host.h   |  2 +-
>  virt/kvm/kvm_main.c        | 20 ++++++++++++++++++--
>  8 files changed, 25 insertions(+), 75 deletions(-)
> 
> diff --git a/arch/arm64/kvm/arm.c b/arch/arm64/kvm/arm.c
> index f5490afe1ebf..75bb7215da03 100644
> --- a/arch/arm64/kvm/arm.c
> +++ b/arch/arm64/kvm/arm.c
> @@ -175,19 +175,11 @@ vm_fault_t kvm_arch_vcpu_fault(struct kvm_vcpu *vcpu, struct vm_fault *vmf)
>   */
>  void kvm_arch_destroy_vm(struct kvm *kvm)
>  {
> -	int i;
> -
>  	bitmap_free(kvm->arch.pmu_filter);
>  
>  	kvm_vgic_destroy(kvm);
>  
> -	for (i = 0; i < KVM_MAX_VCPUS; ++i) {
> -		if (kvm->vcpus[i]) {
> -			kvm_vcpu_destroy(kvm->vcpus[i]);
> -			kvm->vcpus[i] = NULL;
> -		}
> -	}
> -	atomic_set(&kvm->online_vcpus, 0);
> +	kvm_destroy_vcpus(kvm);
>  }
>  
>  int kvm_vm_ioctl_check_extension(struct kvm *kvm, long ext)
> diff --git a/arch/mips/kvm/mips.c b/arch/mips/kvm/mips.c
> index 562aa878b266..ceacca74f808 100644
> --- a/arch/mips/kvm/mips.c
> +++ b/arch/mips/kvm/mips.c
> @@ -171,25 +171,6 @@ int kvm_arch_init_vm(struct kvm *kvm, unsigned long type)
>  	return 0;
>  }
>  
> -void kvm_mips_free_vcpus(struct kvm *kvm)
> -{
> -	unsigned int i;
> -	struct kvm_vcpu *vcpu;
> -
> -	kvm_for_each_vcpu(i, vcpu, kvm) {
> -		kvm_vcpu_destroy(vcpu);
> -	}
> -
> -	mutex_lock(&kvm->lock);
> -
> -	for (i = 0; i < atomic_read(&kvm->online_vcpus); i++)
> -		kvm->vcpus[i] = NULL;
> -
> -	atomic_set(&kvm->online_vcpus, 0);
> -
> -	mutex_unlock(&kvm->lock);
> -}
> -
>  static void kvm_mips_free_gpa_pt(struct kvm *kvm)
>  {
>  	/* It should always be safe to remove after flushing the whole range */
> @@ -199,7 +180,7 @@ static void kvm_mips_free_gpa_pt(struct kvm *kvm)
>  
>  void kvm_arch_destroy_vm(struct kvm *kvm)
>  {
> -	kvm_mips_free_vcpus(kvm);
> +	kvm_destroy_vcpus(kvm);
>  	kvm_mips_free_gpa_pt(kvm);
>  }
>  
> diff --git a/arch/powerpc/kvm/powerpc.c b/arch/powerpc/kvm/powerpc.c
> index 35e9cccdeef9..492e4a4121cb 100644
> --- a/arch/powerpc/kvm/powerpc.c
> +++ b/arch/powerpc/kvm/powerpc.c
> @@ -463,9 +463,6 @@ int kvm_arch_init_vm(struct kvm *kvm, unsigned long type)
>  
>  void kvm_arch_destroy_vm(struct kvm *kvm)
>  {
> -	unsigned int i;
> -	struct kvm_vcpu *vcpu;
> -
>  #ifdef CONFIG_KVM_XICS
>  	/*
>  	 * We call kick_all_cpus_sync() to ensure that all
> @@ -476,14 +473,9 @@ void kvm_arch_destroy_vm(struct kvm *kvm)
>  		kick_all_cpus_sync();
>  #endif
>  
> -	kvm_for_each_vcpu(i, vcpu, kvm)
> -		kvm_vcpu_destroy(vcpu);
> +	kvm_destroy_vcpus(kvm);
>  
>  	mutex_lock(&kvm->lock);
> -	for (i = 0; i < atomic_read(&kvm->online_vcpus); i++)
> -		kvm->vcpus[i] = NULL;
> -
> -	atomic_set(&kvm->online_vcpus, 0);
>  
>  	kvmppc_core_destroy_vm(kvm);
>  
> diff --git a/arch/riscv/kvm/vm.c b/arch/riscv/kvm/vm.c
> index 26399df15b63..6af6cde295eb 100644
> --- a/arch/riscv/kvm/vm.c
> +++ b/arch/riscv/kvm/vm.c
> @@ -46,15 +46,7 @@ int kvm_arch_init_vm(struct kvm *kvm, unsigned long type)
>  
>  void kvm_arch_destroy_vm(struct kvm *kvm)
>  {
> -	int i;
> -
> -	for (i = 0; i < KVM_MAX_VCPUS; ++i) {
> -		if (kvm->vcpus[i]) {
> -			kvm_vcpu_destroy(kvm->vcpus[i]);
> -			kvm->vcpus[i] = NULL;
> -		}
> -	}
> -	atomic_set(&kvm->online_vcpus, 0);
> +	kvm_destroy_vcpus(kvm);
>  }
>  
>  int kvm_vm_ioctl_check_extension(struct kvm *kvm, long ext)
> diff --git a/arch/s390/kvm/kvm-s390.c b/arch/s390/kvm/kvm-s390.c
> index c6257f625929..7af53b8788fa 100644
> --- a/arch/s390/kvm/kvm-s390.c
> +++ b/arch/s390/kvm/kvm-s390.c
> @@ -2819,27 +2819,11 @@ void kvm_arch_vcpu_destroy(struct kvm_vcpu *vcpu)
>  	free_page((unsigned long)(vcpu->arch.sie_block));
>  }
>  
> -static void kvm_free_vcpus(struct kvm *kvm)
> -{
> -	unsigned int i;
> -	struct kvm_vcpu *vcpu;
> -
> -	kvm_for_each_vcpu(i, vcpu, kvm)
> -		kvm_vcpu_destroy(vcpu);
> -
> -	mutex_lock(&kvm->lock);
> -	for (i = 0; i < atomic_read(&kvm->online_vcpus); i++)
> -		kvm->vcpus[i] = NULL;
> -
> -	atomic_set(&kvm->online_vcpus, 0);
> -	mutex_unlock(&kvm->lock);
> -}
> -
>  void kvm_arch_destroy_vm(struct kvm *kvm)
>  {
>  	u16 rc, rrc;
>  
> -	kvm_free_vcpus(kvm);
> +	kvm_destroy_vcpus(kvm);
>  	sca_dispose(kvm);
>  	kvm_s390_gisa_destroy(kvm);
>  	/*
> diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
> index c1c4e2b05a63..498a43126615 100644
> --- a/arch/x86/kvm/x86.c
> +++ b/arch/x86/kvm/x86.c
> @@ -11302,15 +11302,8 @@ static void kvm_free_vcpus(struct kvm *kvm)
>  		kvm_clear_async_pf_completion_queue(vcpu);
>  		kvm_unload_vcpu_mmu(vcpu);
>  	}
> -	kvm_for_each_vcpu(i, vcpu, kvm)
> -		kvm_vcpu_destroy(vcpu);
> -
> -	mutex_lock(&kvm->lock);
> -	for (i = 0; i < atomic_read(&kvm->online_vcpus); i++)
> -		kvm->vcpus[i] = NULL;
>  
> -	atomic_set(&kvm->online_vcpus, 0);
> -	mutex_unlock(&kvm->lock);
> +	kvm_destroy_vcpus(kvm);
>  }
>  
>  void kvm_arch_sync_events(struct kvm *kvm)
> diff --git a/include/linux/kvm_host.h b/include/linux/kvm_host.h
> index 60a35d9fe259..36967291b8c6 100644
> --- a/include/linux/kvm_host.h
> +++ b/include/linux/kvm_host.h
> @@ -725,7 +725,7 @@ static inline struct kvm_vcpu *kvm_get_vcpu_by_id(struct kvm *kvm, int id)
>  		if (WARN_ON_ONCE(!memslot->npages)) {			\
>  		} else
>  
> -void kvm_vcpu_destroy(struct kvm_vcpu *vcpu);
> +void kvm_destroy_vcpus(struct kvm *kvm);
>  
>  void vcpu_load(struct kvm_vcpu *vcpu);
>  void vcpu_put(struct kvm_vcpu *vcpu);
> diff --git a/virt/kvm/kvm_main.c b/virt/kvm/kvm_main.c
> index 3f6d450355f0..d83553eeea21 100644
> --- a/virt/kvm/kvm_main.c
> +++ b/virt/kvm/kvm_main.c
> @@ -435,7 +435,7 @@ static void kvm_vcpu_init(struct kvm_vcpu *vcpu, struct kvm *kvm, unsigned id)
>  	vcpu->last_used_slot = 0;
>  }
>  
> -void kvm_vcpu_destroy(struct kvm_vcpu *vcpu)
> +static void kvm_vcpu_destroy(struct kvm_vcpu *vcpu)
>  {
>  	kvm_dirty_ring_free(&vcpu->dirty_ring);
>  	kvm_arch_vcpu_destroy(vcpu);
> @@ -450,7 +450,23 @@ void kvm_vcpu_destroy(struct kvm_vcpu *vcpu)
>  	free_page((unsigned long)vcpu->run);
>  	kmem_cache_free(kvm_vcpu_cache, vcpu);
>  }
> -EXPORT_SYMBOL_GPL(kvm_vcpu_destroy);
> +
> +void kvm_destroy_vcpus(struct kvm *kvm)
> +{
> +	unsigned int i;
> +	struct kvm_vcpu *vcpu;
> +
> +	kvm_for_each_vcpu(i, vcpu, kvm)
> +		kvm_vcpu_destroy(vcpu);
> +
> +	mutex_lock(&kvm->lock);
> +	for (i = 0; i < atomic_read(&kvm->online_vcpus); i++)
> +		kvm->vcpus[i] = NULL;
> +
> +	atomic_set(&kvm->online_vcpus, 0);
> +	mutex_unlock(&kvm->lock);
> +}
> +EXPORT_SYMBOL_GPL(kvm_destroy_vcpus);
>  
>  #if defined(CONFIG_MMU_NOTIFIER) && defined(KVM_ARCH_WANT_MMU_NOTIFIER)
>  static inline struct kvm *mmu_notifier_to_kvm(struct mmu_notifier *mn)

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