KVM: s390: Optimize ucontrol path

Since commit 7c470539c95630c1f2a10f109e96f249730b75eb
(s390/kvm: avoid automatic sie reentry) we will run through the C code
of KVM on host interrupts instead of just reentering the guest. This
will result in additional ucontrol exits (at least HZ per second). Let
handle a 0 intercept in the kernel and dont return to userspace,
even if in ucontrol mode.

Signed-off-by: Christian Borntraeger <borntraeger@de.ibm.com>
Reviewed-by: Cornelia Huck <cornelia.huck@de.ibm.com>
CC: stable@vger.kernel.org

diff --git a/arch/s390/kvm/kvm-s390.c b/arch/s390/kvm/kvm-s390.c
index 6268357..7337c57 100644 (file)
--- a/arch/s390/kvm/kvm-s390.c
+++ b/arch/s390/kvm/kvm-s390.c
@@ -896,7 +896,8 @@ static int vcpu_post_run(struct kvm_vcpu *vcpu, int exit_reason)
 
        if (rc == 0) {
                if (kvm_is_ucontrol(vcpu->kvm))
-                       rc = -EOPNOTSUPP;
+                       /* Don't exit for host interrupts. */
+                       rc = vcpu->arch.sie_block->icptcode ? -EOPNOTSUPP : 0;
                else
                        rc = kvm_handle_sie_intercept(vcpu);
        }