On Tue, 21 Nov 2017 16:18:53 +0100 David Hildenbrand <david@xxxxxxxxxx> wrote: > On 21.11.2017 16:08, Christian Borntraeger wrote: > > 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@xxxxxxxxxx> > > --- > > 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) { > > I don't see the need for if (do I need more coffee?). I think the if can be dropped and flags zeroed unconditionally, as we can't do anything special for flags != 0 anyway. > > > + /* > > + * 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) { > > dito > > > + /* see above */ > > /* same handling as for kvm_s390_set_irq_state() */ I like that comment better. > > > + irq_state.flags = 0; > > + } > > r = kvm_s390_get_irq_state(vcpu, > > (__u8 __user *) irq_state.buf, > > irq_state.len); > > > > We should also document this in Documentation/virtual/kvm/api.txt, I think. (Checking, the documentation for set_irq_state also seems wrong.) -- To unsubscribe from this list: send the line "unsubscribe linux-s390" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html