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Commit 5de72a22 authored by Christian Borntraeger's avatar Christian Borntraeger
Browse files

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

Signed-off-by: default avatarChristian Borntraeger <borntraeger@de.ibm.com>
Acked-by: default avatarPaul E. McKenney <paulmck@linux.vnet.ibm.com>
parent 488beef1

arch/s390/kvm/gaccess.c

+6 −12
Original line number Diff line number Diff line
@@ -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)