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>

diff --git a/arch/s390/kvm/gaccess.c b/arch/s390/kvm/gaccess.c
index 6dc0ad9c7050a11bb812884285a398a48530e6c6..8f195fa904a1eaf82fbf711ad12c02e7371ffe02 100644 (file)
--- 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)