[PATCH 3.12 030/182] KVM: s390: Optimize ucontrol path

[Jiri Slaby]

From: Christian Borntraeger <borntraeger@xxxxxxxxxx>

3.12-stable review patch.  If anyone has any objections, please let me know.

===============

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@xxxxxxxxxx>
Reviewed-by: Cornelia Huck <cornelia.huck@xxxxxxxxxx>
Signed-off-by: Jiri Slaby <jslaby@xxxxxxx>
---
 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 776dafe918db..48bb1c129963 100644
--- a/arch/s390/kvm/kvm-s390.c
+++ b/arch/s390/kvm/kvm-s390.c
@@ -788,7 +788,8 @@ rerun_vcpu:
 		if (rc)
 			break;
 		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);
 	} while (!signal_pending(current) && !rc);
-- 
1.9.3

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