[PATCH 1/1] KVM: s390: mark irq_state.flags as non-usable

[Christian Borntraeger <borntraeger@de.ibm.com>]

Old kernels did not check for zero in the irq_state.flags field and old
QEMUs did not zero the flag field when calling KVM_S390_*_IRQ_STATE.
Let's add a comment and dummy code to prevent future usage of flags
and pad.

Signed-off-by: Christian Borntraeger <borntraeger@de.ibm.com>
---
 arch/s390/kvm/kvm-s390.c | 14 ++++++++++++++
 1 file changed, 14 insertions(+)

diff --git a/arch/s390/kvm/kvm-s390.c b/arch/s390/kvm/kvm-s390.c
index 6a5e02f..1baa393 100644
--- a/arch/s390/kvm/kvm-s390.c
+++ b/arch/s390/kvm/kvm-s390.c
@@ -3834,6 +3834,16 @@ long kvm_arch_vcpu_ioctl(struct file *filp,
 			r = -EINVAL;
 			break;
 		}
+		if (irq_state.flags) {
+			/*
+			 * This is a placeholder to make sure that nobody uses
+			 * flags and pad. Old kernels did not check for zero
+			 * and old QEMUs did not zero the flag field.
+			 * That means that we cannot use the flags field for
+			 * any possible extension.
+			 */
+			irq_state.flags = 0;
+		}
 		r = kvm_s390_set_irq_state(vcpu,
 					   (void __user *) irq_state.buf,
 					   irq_state.len);
@@ -3849,6 +3859,10 @@ long kvm_arch_vcpu_ioctl(struct file *filp,
 			r = -EINVAL;
 			break;
 		}
+		if (irq_state.flags) {
+			/* see above */
+			irq_state.flags = 0;
+		}
 		r = kvm_s390_get_irq_state(vcpu,
 					   (__u8 __user *)  irq_state.buf,
 					   irq_state.len);
-- 
2.9.4