linux-kernel - Re: [PATCH 1/2] KVM: s390: gaccess: Cleanup access to guest frames

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Date:   Wed, 18 Aug 2021 09:46:46 +0200
From:   Janosch Frank <frankja@...ux.ibm.com>
To:     Janis Schoetterl-Glausch <scgl@...ux.ibm.com>, kvm@...r.kernel.org,
        borntraeger@...ibm.com, imbrenda@...ux.ibm.com,
        Heiko Carstens <hca@...ux.ibm.com>,
        Vasily Gorbik <gor@...ux.ibm.com>
Cc:     david@...hat.com, cohuck@...hat.com, linux-s390@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH 1/2] KVM: s390: gaccess: Cleanup access to guest frames

On 8/16/21 5:07 PM, Janis Schoetterl-Glausch wrote:
> Introduce a helper function for guest frame access.
> Rewrite the calculation of the gpa and the length of the segment
> to be more readable.
> 
> Signed-off-by: Janis Schoetterl-Glausch <scgl@...ux.ibm.com>

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

> ---
>  arch/s390/kvm/gaccess.c | 48 +++++++++++++++++++++++++----------------
>  1 file changed, 29 insertions(+), 19 deletions(-)
> 
> diff --git a/arch/s390/kvm/gaccess.c b/arch/s390/kvm/gaccess.c
> index b9f85b2dc053..df83de0843de 100644
> --- a/arch/s390/kvm/gaccess.c
> +++ b/arch/s390/kvm/gaccess.c
> @@ -827,11 +827,26 @@ static int guest_page_range(struct kvm_vcpu *vcpu, unsigned long ga, u8 ar,
>  	return 0;
>  }
>  
> +static int access_guest_frame(struct kvm *kvm, enum gacc_mode mode, gpa_t gpa,
> +			      void *data, unsigned int len)
> +{
> +	gfn_t gfn = gpa_to_gfn(gpa);
> +	unsigned int offset = offset_in_page(gpa);
> +	int rc;
> +
> +	if (mode == GACC_STORE)
> +		rc = kvm_write_guest_page(kvm, gfn, data, offset, len);
> +	else
> +		rc = kvm_read_guest_page(kvm, gfn, data, offset, len);
> +	return rc;
> +}
> +
>  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 seg;
>  	unsigned long pages_array[2];
>  	unsigned long *pages;
>  	int need_ipte_lock;
> @@ -855,15 +870,12 @@ 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);
> -		if (mode == GACC_STORE)
> -			rc = kvm_write_guest(vcpu->kvm, gpa, data, _len);
> -		else
> -			rc = kvm_read_guest(vcpu->kvm, gpa, data, _len);
> -		len -= _len;
> -		ga += _len;
> -		data += _len;
> +		gpa = pages[idx] + offset_in_page(ga);
> +		seg = min(PAGE_SIZE - offset_in_page(gpa), len);
> +		rc = access_guest_frame(vcpu->kvm, mode, gpa, data, seg);
> +		len -= seg;
> +		ga += seg;
> +		data += seg;
>  	}
>  	if (need_ipte_lock)
>  		ipte_unlock(vcpu);
> @@ -875,19 +887,17 @@ 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 long gpa;
> +	unsigned int seg;
>  	int rc = 0;
>  
>  	while (len && !rc) {
>  		gpa = kvm_s390_real_to_abs(vcpu, gra);
> -		_len = min(PAGE_SIZE - (gpa & ~PAGE_MASK), len);
> -		if (mode)
> -			rc = write_guest_abs(vcpu, gpa, data, _len);
> -		else
> -			rc = read_guest_abs(vcpu, gpa, data, _len);
> -		len -= _len;
> -		gra += _len;
> -		data += _len;
> +		seg = min(PAGE_SIZE - offset_in_page(gpa), len);
> +		rc = access_guest_frame(vcpu->kvm, mode, gpa, data, seg);
> +		len -= seg;
> +		gra += seg;
> +		data += seg;
>  	}
>  	return rc;
>  }
>