linux-kernel - Re: [PATCH v7 09/14] KVM: s390: Dispatch to implementing function at top level of vm mem

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Message-ID: <f37f0057-c872-4cb0-fd15-12d2ef280f49@linux.ibm.com>
Date:   Tue, 7 Feb 2023 14:08:54 +0100
From:   Janosch Frank <frankja@...ux.ibm.com>
To:     Janis Schoetterl-Glausch <scgl@...ux.ibm.com>,
        Christian Borntraeger <borntraeger@...ux.ibm.com>,
        Claudio Imbrenda <imbrenda@...ux.ibm.com>,
        Heiko Carstens <hca@...ux.ibm.com>,
        Vasily Gorbik <gor@...ux.ibm.com>,
        Alexander Gordeev <agordeev@...ux.ibm.com>
Cc:     David Hildenbrand <david@...hat.com>,
        Jonathan Corbet <corbet@....net>, kvm@...r.kernel.org,
        linux-doc@...r.kernel.org, linux-kernel@...r.kernel.org,
        linux-kselftest@...r.kernel.org, linux-s390@...r.kernel.org,
        Paolo Bonzini <pbonzini@...hat.com>,
        Shuah Khan <shuah@...nel.org>,
        Sven Schnelle <svens@...ux.ibm.com>,
        Thomas Huth <thuth@...hat.com>
Subject: Re: [PATCH v7 09/14] KVM: s390: Dispatch to implementing function at
 top level of vm mem_op

On 2/6/23 17:45, Janis Schoetterl-Glausch wrote:
> Instead of having one function covering all mem_op operations,
> have a function implementing absolute access and dispatch to that
> function in its caller, based on the operation code.
> This way additional future operations can be implemented by adding an
> implementing function without changing existing operations.
> 
> Suggested-by: Janosch Frank <frankja@...ux.ibm.com>
> Signed-off-by: Janis Schoetterl-Glausch <scgl@...ux.ibm.com>
> Reviewed-by: Thomas Huth <thuth@...hat.com>

Reviewed-by: Janosch Frank <frankja@...ux.ibm.com>

> ---
>   arch/s390/kvm/kvm-s390.c | 38 ++++++++++++++++++++++++--------------
>   1 file changed, 24 insertions(+), 14 deletions(-)
> 
> diff --git a/arch/s390/kvm/kvm-s390.c b/arch/s390/kvm/kvm-s390.c
> index 0367c1a7e69a..707967a296f1 100644
> --- a/arch/s390/kvm/kvm-s390.c
> +++ b/arch/s390/kvm/kvm-s390.c
> @@ -2779,7 +2779,7 @@ static int mem_op_validate_common(struct kvm_s390_mem_op *mop, u64 supported_fla
>   	return 0;
>   }
>   
> -static int kvm_s390_vm_mem_op(struct kvm *kvm, struct kvm_s390_mem_op *mop)
> +static int kvm_s390_vm_mem_op_abs(struct kvm *kvm, struct kvm_s390_mem_op *mop)
>   {
>   	void __user *uaddr = (void __user *)mop->buf;
>   	void *tmpbuf = NULL;
> @@ -2790,17 +2790,6 @@ static int kvm_s390_vm_mem_op(struct kvm *kvm, struct kvm_s390_mem_op *mop)
>   	if (r)
>   		return r;
>   
> -	/*
> -	 * This is technically a heuristic only, if the kvm->lock is not
> -	 * taken, it is not guaranteed that the vm is/remains non-protected.
> -	 * This is ok from a kernel perspective, wrongdoing is detected
> -	 * on the access, -EFAULT is returned and the vm may crash the
> -	 * next time it accesses the memory in question.
> -	 * There is no sane usecase to do switching and a memop on two
> -	 * different CPUs at the same time.
> -	 */
> -	if (kvm_s390_pv_get_handle(kvm))
> -		return -EINVAL;
>   	if (!(mop->flags & KVM_S390_MEMOP_F_CHECK_ONLY)) {
>   		tmpbuf = vmalloc(mop->size);
>   		if (!tmpbuf)
> @@ -2841,8 +2830,6 @@ static int kvm_s390_vm_mem_op(struct kvm *kvm, struct kvm_s390_mem_op *mop)
>   		}
>   		break;
>   	}
> -	default:
> -		r = -EINVAL;
>   	}
>   
>   out_unlock:
> @@ -2852,6 +2839,29 @@ static int kvm_s390_vm_mem_op(struct kvm *kvm, struct kvm_s390_mem_op *mop)
>   	return r;
>   }
>   
> +static int kvm_s390_vm_mem_op(struct kvm *kvm, struct kvm_s390_mem_op *mop)
> +{
> +	/*
> +	 * This is technically a heuristic only, if the kvm->lock is not
> +	 * taken, it is not guaranteed that the vm is/remains non-protected.
> +	 * This is ok from a kernel perspective, wrongdoing is detected
> +	 * on the access, -EFAULT is returned and the vm may crash the
> +	 * next time it accesses the memory in question.
> +	 * There is no sane usecase to do switching and a memop on two
> +	 * different CPUs at the same time.
> +	 */
> +	if (kvm_s390_pv_get_handle(kvm))
> +		return -EINVAL;
> +
> +	switch (mop->op) {
> +	case KVM_S390_MEMOP_ABSOLUTE_READ:
> +	case KVM_S390_MEMOP_ABSOLUTE_WRITE:
> +		return kvm_s390_vm_mem_op_abs(kvm, mop);
> +	default:
> +		return -EINVAL;
> +	}
> +}
> +
>   long kvm_arch_vm_ioctl(struct file *filp,
>   		       unsigned int ioctl, unsigned long arg)
>   {