KVM: s390/cmm: Fix prefix handling for diag 10 balloon

The old handling of prefix pages was broken in the diag10 ballooner.
We now rely on gmap_discard to check for start > end and do a
slow path if the prefix swap pages are affected:
1. discard the pages from start to prefix
2. discard the absolute 0 pages
3. discard the pages after prefix swap to end

Signed-off-by: Christian Borntraeger <borntraeger@de.ibm.com>
Reviewed-by: Thomas Huth <thuth@linux.vnet.ibm.com>

diff --git a/arch/s390/kvm/diag.c b/arch/s390/kvm/diag.c
index b374b6cb778534bd22b8dd9e222d779d7901fa73..9254afff250c968682db79c453d0542868bfdd9c 100644 (file)
--- a/arch/s390/kvm/diag.c
+++ b/arch/s390/kvm/diag.c
@@ -28,22 +28,32 @@ static int diag_release_pages(struct kvm_vcpu *vcpu)
        start = vcpu->run->s.regs.gprs[(vcpu->arch.sie_block->ipa & 0xf0) >> 4];
        end = vcpu->run->s.regs.gprs[vcpu->arch.sie_block->ipa & 0xf] + 4096;
 
-       if (start & ~PAGE_MASK || end & ~PAGE_MASK || start > end
+       if (start & ~PAGE_MASK || end & ~PAGE_MASK || start >= end
            || start < 2 * PAGE_SIZE)
                return kvm_s390_inject_program_int(vcpu, PGM_SPECIFICATION);
 
        VCPU_EVENT(vcpu, 5, "diag release pages %lX %lX", start, end);
        vcpu->stat.diagnose_10++;
 
-       /* we checked for start > end above */
-       if (end < prefix || start >= prefix + 2 * PAGE_SIZE) {
+       /*
+        * We checked for start >= end above, so lets check for the
+        * fast path (no prefix swap page involved)
+        */
+       if (end <= prefix || start >= prefix + 2 * PAGE_SIZE) {
                gmap_discard(vcpu->arch.gmap, start, end);
        } else {
-               if (start < prefix)
-                       gmap_discard(vcpu->arch.gmap, start, prefix);
-               if (end >= prefix)
-                       gmap_discard(vcpu->arch.gmap,
-                                    prefix + 2 * PAGE_SIZE, end);
+               /*
+                * This is slow path.  gmap_discard will check for start
+                * so lets split this into before prefix, prefix, after
+                * prefix and let gmap_discard make some of these calls
+                * NOPs.
+                */
+               gmap_discard(vcpu->arch.gmap, start, prefix);
+               if (start <= prefix)
+                       gmap_discard(vcpu->arch.gmap, 0, 4096);
+               if (end > prefix + 4096)
+                       gmap_discard(vcpu->arch.gmap, 4096, 8192);
+               gmap_discard(vcpu->arch.gmap, prefix + 2 * PAGE_SIZE, end);
        }
        return 0;
 }