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.)
