Re: [PATCH v1 3/8] KVM: s390: Fix unlikely race with KVM_CAP_S390_USER_OPEREXEC

[Eric Farman]

On Thu, 2026-07-02 at 17:24 +0200, Claudio Imbrenda wrote:
> Due to a missing barrier, it was theoretically possible that a vCPU
> being created concurrently with enabling KVM_CAP_S390_USER_OPEREXEC
> would end up with the capability not enabled.
> 
> Fix by using WRITE_ONCE(), which is enough on s390.
> 
> Fixes: 8e8678e740ec ("KVM: s390: Add capability that forwards operation exceptions")
> Signed-off-by: Claudio Imbrenda <imbrenda@xxxxxxxxxxxxx>
> ---
>  arch/s390/kvm/kvm-s390.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)

Thanks, Claudio. FWIW,

Reviewed-by: Eric Farman <farman@xxxxxxxxxxxxx>

> 
> diff --git a/arch/s390/kvm/kvm-s390.c b/arch/s390/kvm/kvm-s390.c
> index 4a6d903e3523..784f7d9c79c7 100644
> --- a/arch/s390/kvm/kvm-s390.c
> +++ b/arch/s390/kvm/kvm-s390.c
> @@ -955,7 +955,7 @@ int kvm_vm_ioctl_enable_cap(struct kvm *kvm, struct kvm_enable_cap *cap)
>  		break;
>  	case KVM_CAP_S390_USER_OPEREXEC:
>  		VM_EVENT(kvm, 3, "%s", "ENABLE: CAP_S390_USER_OPEREXEC");
> -		kvm->arch.user_operexec = 1;
> +		WRITE_ONCE(kvm->arch.user_operexec, 1);
>  		icpt_operexc_on_all_vcpus(kvm);
>  		r = 0;
>  		break;