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
next prev parent reply other threads:[~2021-08-18 7:54 UTC|newest]
Thread overview: 13+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-08-16 15:07 [PATCH 0/2] KVM: s390: Some gaccess cleanup Janis Schoetterl-Glausch
2021-08-16 15:07 ` [PATCH 1/2] KVM: s390: gaccess: Cleanup access to guest frames 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
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