Commit 42400d99 authored by Heiko Carstens's avatar Heiko Carstens
Browse files

KVM: s390: interrupt: use READ_ONCE() before cmpxchg() 



Use READ_ONCE() before cmpxchg() to prevent that the compiler generates
code that fetches the to be compared old value several times from memory.

Reviewed-by: default avatarChristian Borntraeger <borntraeger@linux.ibm.com>
Acked-by: default avatarChristian Borntraeger <borntraeger@linux.ibm.com>
Reviewed-by: default avatarClaudio Imbrenda <imbrenda@linux.ibm.com>
Link: https://lore.kernel.org/r/20230109145456.2895385-1-hca@linux.ibm.com


Signed-off-by: default avatarHeiko Carstens <hca@linux.ibm.com>
parent e3f360db

arch/s390/kvm/interrupt.c

+8 −4
Original line number Diff line number Diff line
@@ -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);

	}