KVM: s390: Fix ordering when adding to SCA

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")
Reviewed-by: Steffen Eiden <seiden@linux.ibm.com>
Reviewed-by: Janosch Frank <frankja@linux.ibm.com>
Signed-off-by: Claudio Imbrenda <imbrenda@linux.ibm.com>
Message-ID: <20260803124040.126471-13-imbrenda@linux.ibm.com>

diff --git a/arch/s390/kvm/kvm-s390.c b/arch/s390/kvm/kvm-s390.c
index 9b8a35e7dc822ef64df68dbab6da457d8b8f16df..518a69c55e85c91cd923a18f56289635372aa7cb 100644 (file)
--- a/arch/s390/kvm/kvm-s390.c
+++ b/arch/s390/kvm/kvm-s390.c
@@ -3485,8 +3485,8 @@ 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)