[PATCH AUTOSEL 3.18 03/98] s390/kvm: REPLACE barrier fixup with READ_ONCE

Sasha Levin
2018-10-25T14:17:18Z

From: Christian Borntraeger <borntraeger@de.ibm.com>

[ Upstream commit 5de72a2247ac05bde7c89039631b3d0c6186fafb ]

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>
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
arch/s390/kvm/gaccess.c | 18 ++++++------------
1 file 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)
--
2.17.1