s390/kvm: REPLACE barrier fixup with READ_ONCE

ACCESS_ONCE does not work reliably on non-scalar types. For
example gcc 4.6 and 4.7 might remove the volatile tag for such
accesses during the SRA (scalar replacement of aggregates) step
(https://gcc.gnu.org/bugzilla/show_bug.cgi?id=58145)

Commit 1365039d0cb3 ("KVM: s390: Fix ipte locking") replace
ACCESS_ONCE with barriers. Lets use READ_ONCE instead.

Signed-off-by: Christian Borntraeger <borntraeger@de.ibm.com>
Acked-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>

1 files changed, 6 insertions, 12 deletions

diff --git a/arch/s390/kvm/gaccess.c b/arch/s390/kvm/gaccess.c
index 6dc0ad9c7050..8f195fa904a1 100644
--- a/arch/s390/kvm/gaccess.c
+++ b/arch/s390/kvm/gaccess.c
@@ -229,12 +229,10 @@ static void ipte_lock_simple(struct kvm_vcpu *vcpu)
                 goto out;
         ic = &vcpu->kvm->arch.sca->ipte_control;
         do {
-                old = *ic;
-                barrier();
+                old = READ_ONCE(*ic);
                 while (old.k) {
                         cond_resched();
-                        old = *ic;
-                        barrier();
+                        old = READ_ONCE(*ic);
                 }
                 new = old;
                 new.k = 1;
@@ -253,8 +251,7 @@ static void ipte_unlock_simple(struct kvm_vcpu *vcpu)
                 goto out;
         ic = &vcpu->kvm->arch.sca->ipte_control;
         do {
-                old = *ic;
-                barrier();
+                old = READ_ONCE(*ic);
                 new = old;
                 new.k = 0;
         } while (cmpxchg(&ic->val, old.val, new.val) != old.val);
@@ -269,12 +266,10 @@ static void ipte_lock_siif(struct kvm_vcpu *vcpu)
 
         ic = &vcpu->kvm->arch.sca->ipte_control;
         do {
-                old = *ic;
-                barrier();
+                old = READ_ONCE(*ic);
                 while (old.kg) {
                         cond_resched();
-                        old = *ic;
-                        barrier();
+                        old = READ_ONCE(*ic);
                 }
                 new = old;
                 new.k = 1;
@@ -288,8 +283,7 @@ static void ipte_unlock_siif(struct kvm_vcpu *vcpu)
 
         ic = &vcpu->kvm->arch.sca->ipte_control;
         do {
-                old = *ic;
-                barrier();
+                old = READ_ONCE(*ic);
                 new = old;
                 new.kh--;
                 if (!new.kh)