linux-kernel - Re: [PATCH v3 1/3] KVM: s390: gaccess: Refactor gpa and length calculation

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Message-ID: <20211129095528.1a92e72d@p-imbrenda>
Date:   Mon, 29 Nov 2021 09:55:28 +0100
From:   Claudio Imbrenda <imbrenda@...ux.ibm.com>
To:     Janis Schoetterl-Glausch <scgl@...ux.ibm.com>
Cc:     Christian Borntraeger <borntraeger@...ibm.com>,
        Janosch Frank <frankja@...ux.ibm.com>,
        Heiko Carstens <hca@...ux.ibm.com>,
        Vasily Gorbik <gor@...ux.ibm.com>,
        David Hildenbrand <david@...hat.com>,
        Alexander Gordeev <agordeev@...ux.ibm.com>,
        kvm@...r.kernel.org, linux-s390@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH v3 1/3] KVM: s390: gaccess: Refactor gpa and length
 calculation

On Fri, 26 Nov 2021 17:45:47 +0100
Janis Schoetterl-Glausch <scgl@...ux.ibm.com> wrote:

> Improve readability by 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>

Reviewed-by: Claudio Imbrenda <imbrenda@...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..45966fbba182 100644
> --- a/arch/s390/kvm/gaccess.c
> +++ b/arch/s390/kvm/gaccess.c
> @@ -831,8 +831,9 @@ 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 long pages_array[2];
> +	unsigned int fragment_len;
>  	unsigned long *pages;
>  	int need_ipte_lock;
>  	union asce asce;
> @@ -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;
>  }