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SubjectRe: [PATCH 8/9] s390/kvm: REPLACE ACCESS_ONCE with READ_ONCE
On Wed, Dec 03, 2014 at 11:30:20PM +0100, Christian Borntraeger wrote:
> 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)
>
> Change the ipte lock code to replace ACCESS_ONCE with READ_ONCE.
>
> Signed-off-by: Christian Borntraeger <borntraeger@de.ibm.com>

Acked-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>

> ---
> arch/s390/kvm/gaccess.c | 14 ++++++++------
> 1 file changed, 8 insertions(+), 6 deletions(-)
>
> diff --git a/arch/s390/kvm/gaccess.c b/arch/s390/kvm/gaccess.c
> index 0f961a1..8f195fa 100644
> --- a/arch/s390/kvm/gaccess.c
> +++ b/arch/s390/kvm/gaccess.c
> @@ -229,10 +229,10 @@ static void ipte_lock_simple(struct kvm_vcpu *vcpu)
> goto out;
> ic = &vcpu->kvm->arch.sca->ipte_control;
> do {
> - old = ACCESS_ONCE(*ic);
> + old = READ_ONCE(*ic);
> while (old.k) {
> cond_resched();
> - old = ACCESS_ONCE(*ic);
> + old = READ_ONCE(*ic);
> }
> new = old;
> new.k = 1;
> @@ -251,7 +251,8 @@ static void ipte_unlock_simple(struct kvm_vcpu *vcpu)
> goto out;
> ic = &vcpu->kvm->arch.sca->ipte_control;
> do {
> - new = old = ACCESS_ONCE(*ic);
> + old = READ_ONCE(*ic);
> + new = old;
> new.k = 0;
> } while (cmpxchg(&ic->val, old.val, new.val) != old.val);
> wake_up(&vcpu->kvm->arch.ipte_wq);
> @@ -265,10 +266,10 @@ static void ipte_lock_siif(struct kvm_vcpu *vcpu)
>
> ic = &vcpu->kvm->arch.sca->ipte_control;
> do {
> - old = ACCESS_ONCE(*ic);
> + old = READ_ONCE(*ic);
> while (old.kg) {
> cond_resched();
> - old = ACCESS_ONCE(*ic);
> + old = READ_ONCE(*ic);
> }
> new = old;
> new.k = 1;
> @@ -282,7 +283,8 @@ static void ipte_unlock_siif(struct kvm_vcpu *vcpu)
>
> ic = &vcpu->kvm->arch.sca->ipte_control;
> do {
> - new = old = ACCESS_ONCE(*ic);
> + old = READ_ONCE(*ic);
> + new = old;
> new.kh--;
> if (!new.kh)
> new.k = 0;
> --
> 1.9.3
>



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