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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 1365039d0c ("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>
This commit is contained in:
Christian Borntraeger 2014-11-25 13:17:34 +01:00
parent 488beef144
commit 5de72a2247
1 changed files with 6 additions and 12 deletions
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18
arch/s390/kvm/gaccess.c
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@ -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)