Re: [PATCH v3 09/10] KVM: s390: Fix ordering when adding to SCA

[Janosch Frank]

On 7/27/26 17:02, Claudio Imbrenda wrote:
> When adding a new vCPU to the SCA area, the validity bit in the MCN was
> set before the pointer to the state description, potentially allowing
> for a race.
>
> Fix by setting the pointer before setting the bit.
>
> Fixes: 14542a0a54c5 ("KVM: S390: Remove sca_lock")
> Signed-off-by: Claudio Imbrenda <imbrenda@xxxxxxxxxxxxx>
> ---
>   arch/s390/kvm/kvm-s390.c | 2 +-
>   1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/arch/s390/kvm/kvm-s390.c b/arch/s390/kvm/kvm-s390.c
> index 8afb88a2b73d..85dcd40b2fa1 100644
> --- a/arch/s390/kvm/kvm-s390.c
> +++ b/arch/s390/kvm/kvm-s390.c
> @@ -3481,8 +3481,8 @@ static void sca_add_vcpu(struct kvm_vcpu *vcpu)
>   	if (!kvm_s390_use_sca_entries())
>   		return;
>   
> +	WRITE_ONCE(sca->cpu[vcpu->vcpu_id].sda, virt_to_phys(vcpu->arch.sie_block));
>   	set_bit_inv(vcpu->vcpu_id, (unsigned long *)sca->mcn);
> -	sca->cpu[vcpu->vcpu_id].sda = virt_to_phys(vcpu->arch.sie_block);
>   }
>   
>   static int sca_can_add_vcpu(struct kvm *kvm, unsigned int id)

Reviewed-by: Janosch Frank <frankja@xxxxxxxxxxxxx>