[PATCH 3.13 051/151] KVM: s390: Optimize ucontrol path

Kamal Mostafa kamal at canonical.com
Fri May 2 15:37:19 UTC 2014 -stable review patch.  If anyone has any objections, please let me know.


From: Christian Borntraeger <borntraeger at de.ibm.com>

commit 2955c83f72801245afd0fe5c560cc75b82bea9aa upstream.

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 at de.ibm.com>
Reviewed-by: Cornelia Huck <cornelia.huck at de.ibm.com>
Signed-off-by: Kamal Mostafa <kamal at canonical.com>
 arch/s390/kvm/kvm-s390.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/arch/s390/kvm/kvm-s390.c b/arch/s390/kvm/kvm-s390.c
index bb383df..bfe7726 100644
--- a/arch/s390/kvm/kvm-s390.c
+++ b/arch/s390/kvm/kvm-s390.c
@@ -746,7 +746,8 @@ 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;
 			rc = kvm_handle_sie_intercept(vcpu);

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