On 8/18/21 9:54 AM, David Hildenbrand wrote:
> 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@xxxxxxxxxxxxx>
>> ---
>> 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()" ?
Ok, I'll use page for consistency's sake.
>
>
>> +{
>> + 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.
Ok
>
>> +
>> + 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.
In access_guest_real we get back the gpa directly from the translation function.
After the next patch the same is true for access_guest.
So using gpas everywhere is nicer.
And if we were to introduce a len_in_page function the offset would not even show up as an intermediary.
>
>> + 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;
>> }
>>
>
>
