LKML Archive on lore.kernel.org
help / color / mirror / Atom feed
From: David Hildenbrand <david@redhat.com>
To: Janis Schoetterl-Glausch <scgl@linux.ibm.com>,
	kvm@vger.kernel.org, borntraeger@de.ibm.com,
	frankja@linux.ibm.com, imbrenda@linux.ibm.com,
	Heiko Carstens <hca@linux.ibm.com>,
	Vasily Gorbik <gor@linux.ibm.com>
Cc: cohuck@redhat.com, linux-s390@vger.kernel.org,
	linux-kernel@vger.kernel.org
Subject: Re: [PATCH 1/2] KVM: s390: gaccess: Cleanup access to guest frames
Date: Wed, 18 Aug 2021 09:54:49 +0200	[thread overview]
Message-ID: <d11128bb-18f6-5210-6f42-74a89d8edcf7@redhat.com> (raw)
In-Reply-To: <20210816150718.3063877-2-scgl@linux.ibm.com>

On 16.08.21 17:07, 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@linux.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)

I know, "frame" is a beautiful term for "page" -- can we just avoid 
using it because we're not using it anywhere else here? :)

What's wrong with "access_guest_page()" ?


> +{
> +	gfn_t gfn = gpa_to_gfn(gpa);
> +	unsigned int offset = offset_in_page(gpa);
> +	int rc;

You could turn both const. You might want to consider 
reverse-christmas-treeing this.

> +
> +	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);

Personally, I prefer passing in pfn + offset instead of a gpa. Also 
avoids having to convert back and forth.

> +	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;

Dito, reverse christmas tree might be worth keeping.

>   	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);

What does "seg" mean? I certainly know when "len" means -- which is also 
what the function eats.

> +		rc = access_guest_frame(vcpu->kvm, mode, gpa, data, seg);
> +		len -= seg;
> +		gra += seg;
> +		data += seg;
>   	}
>   	return rc;
>   }
> 


-- 
Thanks,

David / dhildenb


  parent reply	other threads:[~2021-08-18  7:55 UTC|newest]

Thread overview: 12+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
     [not found] <20210816150718.3063877-1-scgl@linux.ibm.com>
2021-08-16 15:07 ` Janis Schoetterl-Glausch
2021-08-18  7:46   ` Janosch Frank
2021-08-18  7:54   ` David Hildenbrand [this message]
2021-08-18  8:06     ` Janosch Frank
2021-08-18  8:44       ` David Hildenbrand
2021-08-18  8:48         ` Janis Schoetterl-Glausch
2021-08-19 13:53       ` Janis Schoetterl-Glausch
2021-08-19 14:11         ` Janosch Frank
2021-08-18  9:00     ` Janis Schoetterl-Glausch
2021-08-16 15:07 ` [PATCH 2/2] KVM: s390: gaccess: Refactor access address range check Janis Schoetterl-Glausch
2021-08-18 10:08   ` Claudio Imbrenda
2021-08-19 12:39     ` Janis Schoetterl-Glausch

Reply instructions:

You may reply publicly to this message via plain-text email
using any one of the following methods:

* Save the following mbox file, import it into your mail client,
  and reply-to-all from there: mbox

  Avoid top-posting and favor interleaved quoting:
  https://en.wikipedia.org/wiki/Posting_style#Interleaved_style

* Reply using the --to, --cc, and --in-reply-to
  switches of git-send-email(1):

  git send-email \
    --in-reply-to=d11128bb-18f6-5210-6f42-74a89d8edcf7@redhat.com \
    --to=david@redhat.com \
    --cc=borntraeger@de.ibm.com \
    --cc=cohuck@redhat.com \
    --cc=frankja@linux.ibm.com \
    --cc=gor@linux.ibm.com \
    --cc=hca@linux.ibm.com \
    --cc=imbrenda@linux.ibm.com \
    --cc=kvm@vger.kernel.org \
    --cc=linux-kernel@vger.kernel.org \
    --cc=linux-s390@vger.kernel.org \
    --cc=scgl@linux.ibm.com \
    --subject='Re: [PATCH 1/2] KVM: s390: gaccess: Cleanup access to guest frames' \
    /path/to/YOUR_REPLY

  https://kernel.org/pub/software/scm/git/docs/git-send-email.html

* If your mail client supports setting the In-Reply-To header
  via mailto: links, try the mailto: link

This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for NNTP newsgroup(s).