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>

1 files changed, 18 insertions, 8 deletions

diff --git a/arch/s390/kvm/diag.c b/arch/s390/kvm/diag.c
index b374b6cb7785..9254afff250c 100644
--- 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;
 }