linux-kernel - Re: [PATCH 6/7] KVM: arm64: Change return type of kvm_vm_ioctl_mte_copy

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Date:   Tue, 7 Feb 2023 11:09:39 +1100
From:   Gavin Shan <gshan@...hat.com>
To:     Thomas Huth <thuth@...hat.com>, kvm@...r.kernel.org,
        Paolo Bonzini <pbonzini@...hat.com>,
        Sean Christopherson <seanjc@...gle.com>
Cc:     kvmarm@...ts.linux.dev, linux-kernel@...r.kernel.org,
        kvm-riscv@...ts.infradead.org, Marc Zyngier <maz@...nel.org>,
        James Morse <james.morse@....com>,
        Suzuki K Poulose <suzuki.poulose@....com>,
        Oliver Upton <oliver.upton@...ux.dev>,
        Zenghui Yu <yuzenghui@...wei.com>,
        Christian Borntraeger <borntraeger@...ux.ibm.com>,
        Janosch Frank <frankja@...ux.ibm.com>,
        Claudio Imbrenda <imbrenda@...ux.ibm.com>,
        David Hildenbrand <david@...hat.com>,
        linuxppc-dev@...ts.ozlabs.org
Subject: Re: [PATCH 6/7] KVM: arm64: Change return type of
 kvm_vm_ioctl_mte_copy_tags() to "int"

Hi Thomas,

On 2/3/23 8:42 PM, Thomas Huth wrote:
> This function only returns normal integer values, so there is
> no need to declare its return value as "long".
> 
> Signed-off-by: Thomas Huth <thuth@...hat.com>
> ---
>   arch/arm64/include/asm/kvm_host.h | 4 ++--
>   arch/arm64/kvm/guest.c            | 4 ++--
>   2 files changed, 4 insertions(+), 4 deletions(-)
> 
> diff --git a/arch/arm64/include/asm/kvm_host.h b/arch/arm64/include/asm/kvm_host.h
> index 35a159d131b5..b1a16343767f 100644
> --- a/arch/arm64/include/asm/kvm_host.h
> +++ b/arch/arm64/include/asm/kvm_host.h
> @@ -963,8 +963,8 @@ int kvm_arm_vcpu_arch_get_attr(struct kvm_vcpu *vcpu,
>   int kvm_arm_vcpu_arch_has_attr(struct kvm_vcpu *vcpu,
>   			       struct kvm_device_attr *attr);
>   
> -long kvm_vm_ioctl_mte_copy_tags(struct kvm *kvm,
> -				struct kvm_arm_copy_mte_tags *copy_tags);
> +int kvm_vm_ioctl_mte_copy_tags(struct kvm *kvm,
> +			       struct kvm_arm_copy_mte_tags *copy_tags);
>   
>   /* Guest/host FPSIMD coordination helpers */
>   int kvm_arch_vcpu_run_map_fp(struct kvm_vcpu *vcpu);
> diff --git a/arch/arm64/kvm/guest.c b/arch/arm64/kvm/guest.c
> index cf4c495a4321..80e530549c34 100644
> --- a/arch/arm64/kvm/guest.c
> +++ b/arch/arm64/kvm/guest.c
> @@ -1013,8 +1013,8 @@ int kvm_arm_vcpu_arch_has_attr(struct kvm_vcpu *vcpu,
>   	return ret;
>   }
>   
> -long kvm_vm_ioctl_mte_copy_tags(struct kvm *kvm,
> -				struct kvm_arm_copy_mte_tags *copy_tags)
> +int kvm_vm_ioctl_mte_copy_tags(struct kvm *kvm,
> +			       struct kvm_arm_copy_mte_tags *copy_tags)
>   {
>   	gpa_t guest_ipa = copy_tags->guest_ipa;
>   	size_t length = copy_tags->length;
> 

It's possible for the function to return number of bytes have been copied.
Its type is 'size_t', same to 'unsigned long'. So 'int' doesn't have sufficient
space for it if I'm correct.

long kvm_vm_ioctl_mte_copy_tags(struct kvm *kvm,
                                 struct kvm_arm_copy_mte_tags *copy_tags)
{
         gpa_t guest_ipa = copy_tags->guest_ipa;
         size_t length = copy_tags->length;
         :
         :
out:
         mutex_unlock(&kvm->slots_lock);
         /* If some data has been copied report the number of bytes copied */
         if (length != copy_tags->length)
                 return copy_tags->length - length;
         return ret;
}

Thanks,
Gavin