[3.11.y.z extended stable] Patch "KVM: s390: Optimize ucontrol path" has been added to staging queue

Luis Henriques luis.henriques at canonical.com
Wed May 7 11:09:21 UTC 2014

This is a note to let you know that I have just added a patch titled

    KVM: s390: Optimize ucontrol path

to the linux-3.11.y-queue branch of the 3.11.y.z extended stable tree 
which can be found at:


If you, or anyone else, feels it should not be added to this tree, please 
reply to this email.

For more information about the 3.11.y.z tree, see



>From eb81abce47002bd539f0782f263feaa93bfbb424 Mon Sep 17 00:00:00 2001
From: Christian Borntraeger <borntraeger at de.ibm.com>
Date: Thu, 6 Mar 2014 16:01:38 +0100
Subject: KVM: s390: Optimize ucontrol path

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>
[ luis: backported to 3.11: adjusted context ]
Signed-off-by: Luis Henriques <luis.henriques 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 34c1c9a..e13e7af 100644
--- a/arch/s390/kvm/kvm-s390.c
+++ b/arch/s390/kvm/kvm-s390.c
@@ -781,7 +781,8 @@ rerun_vcpu:
 		if (rc)
 		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);
 	} while (!signal_pending(current) && !rc);

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