KVM: s390: fix memory overwrites when not using SCA entries

Even if we don't have extended SCA support, we can have more than 64 CPUs
if we don't enable any HW features that might use the SCA entries.

Now, this works just fine, but we missed a return, which is why we
would actually store the SCA entries. If we have more than 64 CPUs, this
means writing outside of the basic SCA - bad.

Let's fix this. This allows > 64 CPUs when running nested (under vSIE)
without random crashes.

Fixes: a6940674c384 ("KVM: s390: allow 255 VCPUs when sca entries aren't used")
Reported-by: Christian Borntraeger <borntraeger@de.ibm.com>
Tested-by: Christian Borntraeger <borntraeger@de.ibm.com>
Signed-off-by: David Hildenbrand <david@redhat.com>
Message-Id: <20180306132758.21034-1-david@redhat.com>
Cc: stable@vger.kernel.org
Reviewed-by: Cornelia Huck <cohuck@redhat.com>
Signed-off-by: Christian Borntraeger <borntraeger@de.ibm.com>

diff --git a/arch/s390/kvm/kvm-s390.c b/arch/s390/kvm/kvm-s390.c
index df19f158347e0fb87736262cf6fa5a9953baa84e..339ac0964590a1337935ea55ee0cbc7d7c2e441e 100644 (file)
--- a/arch/s390/kvm/kvm-s390.c
+++ b/arch/s390/kvm/kvm-s390.c
@@ -2147,6 +2147,7 @@ static void sca_add_vcpu(struct kvm_vcpu *vcpu)
                /* we still need the basic sca for the ipte control */
                vcpu->arch.sie_block->scaoh = (__u32)(((__u64)sca) >> 32);
                vcpu->arch.sie_block->scaol = (__u32)(__u64)sca;
+               return;
        }
        read_lock(&vcpu->kvm->arch.sca_lock);
        if (vcpu->kvm->arch.use_esca) {