On 8/18/21 9:54 AM, David Hildenbrand wrote:

On 16.08.21 17:07, Janis Schoetterl-Glausch wrote:

quoted

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 <redacted>
---
  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.

quoted

+{
+    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

quoted

+
+    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.

quoted

+    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.

quoted

      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.

quoted

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