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

1 files changed, 2 insertions, 1 deletions

diff --git a/arch/s390/kvm/kvm-s390.c b/arch/s390/kvm/kvm-s390.c
index 62683576f8e2..7337c577e949 100644
--- 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);
         }