Messages in this thread | | | Date | Tue, 10 Jan 2023 20:15:50 +0100 | Subject | Re: [PATCH v2] KVM: s390: interrupt: use READ_ONCE() before cmpxchg() | From | Christian Borntraeger <> |
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Am 09.01.23 um 15:54 schrieb Heiko Carstens: > Use READ_ONCE() before cmpxchg() to prevent that the compiler generates > code that fetches the to be compared old value several times from memory. > > Signed-off-by: Heiko Carstens <hca@linux.ibm.com>
Looks sane.
Reviewed-by: Christian Borntraeger <borntraeger@linux.ibm.com>
In case you want to take it via the s390 tree: Acked-by: Christian Borntraeger <borntraeger@linux.ibm.com>
> --- > > v2: make it compile > > arch/s390/kvm/interrupt.c | 12 ++++++++---- > 1 file changed, 8 insertions(+), 4 deletions(-) > > diff --git a/arch/s390/kvm/interrupt.c b/arch/s390/kvm/interrupt.c > index 1dae78deddf2..ab26aa53ee37 100644 > --- a/arch/s390/kvm/interrupt.c > +++ b/arch/s390/kvm/interrupt.c > @@ -83,8 +83,9 @@ static int sca_inject_ext_call(struct kvm_vcpu *vcpu, int src_id) > struct esca_block *sca = vcpu->kvm->arch.sca; > union esca_sigp_ctrl *sigp_ctrl = > &(sca->cpu[vcpu->vcpu_id].sigp_ctrl); > - union esca_sigp_ctrl new_val = {0}, old_val = *sigp_ctrl; > + union esca_sigp_ctrl new_val = {0}, old_val; > > + old_val = READ_ONCE(*sigp_ctrl); > new_val.scn = src_id; > new_val.c = 1; > old_val.c = 0; > @@ -95,8 +96,9 @@ static int sca_inject_ext_call(struct kvm_vcpu *vcpu, int src_id) > struct bsca_block *sca = vcpu->kvm->arch.sca; > union bsca_sigp_ctrl *sigp_ctrl = > &(sca->cpu[vcpu->vcpu_id].sigp_ctrl); > - union bsca_sigp_ctrl new_val = {0}, old_val = *sigp_ctrl; > + union bsca_sigp_ctrl new_val = {0}, old_val; > > + old_val = READ_ONCE(*sigp_ctrl); > new_val.scn = src_id; > new_val.c = 1; > old_val.c = 0; > @@ -126,16 +128,18 @@ static void sca_clear_ext_call(struct kvm_vcpu *vcpu) > struct esca_block *sca = vcpu->kvm->arch.sca; > union esca_sigp_ctrl *sigp_ctrl = > &(sca->cpu[vcpu->vcpu_id].sigp_ctrl); > - union esca_sigp_ctrl old = *sigp_ctrl; > + union esca_sigp_ctrl old; > > + old = READ_ONCE(*sigp_ctrl); > expect = old.value; > rc = cmpxchg(&sigp_ctrl->value, old.value, 0); > } else { > struct bsca_block *sca = vcpu->kvm->arch.sca; > union bsca_sigp_ctrl *sigp_ctrl = > &(sca->cpu[vcpu->vcpu_id].sigp_ctrl); > - union bsca_sigp_ctrl old = *sigp_ctrl; > + union bsca_sigp_ctrl old; > > + old = READ_ONCE(*sigp_ctrl); > expect = old.value; > rc = cmpxchg(&sigp_ctrl->value, old.value, 0); > }
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