Re: [PATCH v2 3/3] KVM: s390: gaccess: Cleanup access to guest frames

David Hildenbrand
2021-10-28T14:25:13Z

On 28.10.21 15:55, Janis Schoetterl-Glausch wrote:
> Introduce a helper function for guest frame access.

"guest page access"

But I do wonder if you actually want to call it

"access_guest_abs"

and say "guest absolute access" instead here.

Because we're dealing with absolute addresses and the fact that we are
accessing it page-wise is just because we have to perform a page-wise
translation in the callers (either virtual->absolute or real->absolute).

Theoretically, if you know you're across X pages but they are contiguous
in absolute address space, nothing speaks against using that function
directly across X pages with a single call.

>
> Signed-off-by: Janis Schoetterl-Glausch <scgl@linux.ibm.com>
> ---
> arch/s390/kvm/gaccess.c | 24 ++++++++++++++++--------
> 1 file changed, 16 insertions(+), 8 deletions(-)
>
> diff --git a/arch/s390/kvm/gaccess.c b/arch/s390/kvm/gaccess.c
> index f0848c37b003..9a633310b6fe 100644
> --- a/arch/s390/kvm/gaccess.c
> +++ b/arch/s390/kvm/gaccess.c
> @@ -866,6 +866,20 @@ static int guest_range_to_gpas(struct kvm_vcpu *vcpu, unsigned long ga, u8 ar,
> return 0;
> }
>
> +static int access_guest_page(struct kvm *kvm, enum gacc_mode mode, gpa_t gpa,
> + void *data, unsigned int len)
> +{
> + const unsigned int offset = offset_in_page(gpa);
> + const gfn_t gfn = gpa_to_gfn(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)
> {
> @@ -896,10 +910,7 @@ int access_guest(struct kvm_vcpu *vcpu, unsigned long ga, u8 ar, void *data,
> rc = guest_range_to_gpas(vcpu, ga, ar, gpas, len, asce, mode);
> for (idx = 0; idx < nr_pages && !rc; idx++) {
> fragment_len = min(PAGE_SIZE - offset_in_page(gpas[idx]), len);
> - if (mode == GACC_STORE)
> - rc = kvm_write_guest(vcpu->kvm, gpas[idx], data, fragment_len);
> - else
> - rc = kvm_read_guest(vcpu->kvm, gpas[idx], data, fragment_len);
> + rc = access_guest_page(vcpu->kvm, mode, gpas[idx], data, fragment_len);
> len -= fragment_len;
> data += fragment_len;
> }
> @@ -920,10 +931,7 @@ int access_guest_real(struct kvm_vcpu *vcpu, unsigned long gra,
> while (len && !rc) {
> gpa = kvm_s390_real_to_abs(vcpu, gra);
> fragment_len = min(PAGE_SIZE - offset_in_page(gpa), len);
> - if (mode)
> - rc = write_guest_abs(vcpu, gpa, data, fragment_len);
> - else
> - rc = read_guest_abs(vcpu, gpa, data, fragment_len);
> + rc = access_guest_page(vcpu->kvm, mode, gpa, data, fragment_len);
> len -= fragment_len;
> gra += fragment_len;
> data += fragment_len;
>

--
Thanks,

David / dhildenb