linux-kernel - Re: [PATCH v2 1/3] KVM: s390: gaccess: Refactor gpa and length calculation

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Date:   Fri, 19 Nov 2021 09:27:26 +0100
From:   Janosch Frank <frankja@...ux.ibm.com>
To:     Janis Schoetterl-Glausch <scgl@...ux.ibm.com>,
        Christian Borntraeger <borntraeger@...ibm.com>,
        Heiko Carstens <hca@...ux.ibm.com>,
        Vasily Gorbik <gor@...ux.ibm.com>
Cc:     David Hildenbrand <david@...hat.com>,
        Claudio Imbrenda <imbrenda@...ux.ibm.com>,
        Alexander Gordeev <agordeev@...ux.ibm.com>,
        kvm@...r.kernel.org, linux-s390@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2 1/3] KVM: s390: gaccess: Refactor gpa and length
 calculation

On 10/28/21 15:55, Janis Schoetterl-Glausch wrote:
> Improve readability be renaming the length variable and
> not calculating the offset manually.
> 
> Signed-off-by: Janis Schoetterl-Glausch <scgl@...ux.ibm.com>

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

> ---
>   arch/s390/kvm/gaccess.c | 32 +++++++++++++++++---------------
>   1 file changed, 17 insertions(+), 15 deletions(-)
> 
> diff --git a/arch/s390/kvm/gaccess.c b/arch/s390/kvm/gaccess.c
> index 6af59c59cc1b..0d11cea92603 100644
> --- a/arch/s390/kvm/gaccess.c
> +++ b/arch/s390/kvm/gaccess.c
> @@ -831,7 +831,8 @@ int access_guest(struct kvm_vcpu *vcpu, unsigned long ga, u8 ar, void *data,
>   		 unsigned long len, enum gacc_mode mode)
>   {
>   	psw_t *psw = &vcpu->arch.sie_block->gpsw;
> -	unsigned long _len, nr_pages, gpa, idx;
> +	unsigned long nr_pages, gpa, idx;
> +	unsigned int fragment_len;
>   	unsigned long pages_array[2];
>   	unsigned long *pages;
>   	int need_ipte_lock;
> @@ -855,15 +856,15 @@ int access_guest(struct kvm_vcpu *vcpu, unsigned long ga, u8 ar, void *data,
>   		ipte_lock(vcpu);
>   	rc = guest_page_range(vcpu, ga, ar, pages, nr_pages, asce, mode);
>   	for (idx = 0; idx < nr_pages && !rc; idx++) {
> -		gpa = *(pages + idx) + (ga & ~PAGE_MASK);
> -		_len = min(PAGE_SIZE - (gpa & ~PAGE_MASK), len);
> +		gpa = pages[idx] + offset_in_page(ga);
> +		fragment_len = min(PAGE_SIZE - offset_in_page(gpa), len);
>   		if (mode == GACC_STORE)
> -			rc = kvm_write_guest(vcpu->kvm, gpa, data, _len);
> +			rc = kvm_write_guest(vcpu->kvm, gpa, data, fragment_len);
>   		else
> -			rc = kvm_read_guest(vcpu->kvm, gpa, data, _len);
> -		len -= _len;
> -		ga += _len;
> -		data += _len;
> +			rc = kvm_read_guest(vcpu->kvm, gpa, data, fragment_len);
> +		len -= fragment_len;
> +		ga += fragment_len;
> +		data += fragment_len;
>   	}
>   	if (need_ipte_lock)
>   		ipte_unlock(vcpu);
> @@ -875,19 +876,20 @@ int access_guest(struct kvm_vcpu *vcpu, unsigned long ga, u8 ar, void *data,
>   int access_guest_real(struct kvm_vcpu *vcpu, unsigned long gra,
>   		      void *data, unsigned long len, enum gacc_mode mode)
>   {
> -	unsigned long _len, gpa;
> +	unsigned int fragment_len;
> +	unsigned long gpa;
>   	int rc = 0;
>   
>   	while (len && !rc) {
>   		gpa = kvm_s390_real_to_abs(vcpu, gra);
> -		_len = min(PAGE_SIZE - (gpa & ~PAGE_MASK), len);
> +		fragment_len = min(PAGE_SIZE - offset_in_page(gpa), len);
>   		if (mode)
> -			rc = write_guest_abs(vcpu, gpa, data, _len);
> +			rc = write_guest_abs(vcpu, gpa, data, fragment_len);
>   		else
> -			rc = read_guest_abs(vcpu, gpa, data, _len);
> -		len -= _len;
> -		gra += _len;
> -		data += _len;
> +			rc = read_guest_abs(vcpu, gpa, data, fragment_len);
> +		len -= fragment_len;
> +		gra += fragment_len;
> +		data += fragment_len;
>   	}
>   	return rc;
>   }
>