Re: [PATCH v1 4/7] vfio: ap: AP Queue Interrupt Control VFIO ioctl calls

[Pierre Morel]

On 08/11/2018 10:14, Cornelia Huck wrote:
> On Wed, 7 Nov 2018 23:23:40 +0100
> Pierre Morel <pmorel@xxxxxxxxxxxxx> wrote:
>
> > On 07/11/2018 10:46, Cornelia Huck wrote:
> > > On Wed, 31 Oct 2018 19:12:54 +0100
> > > Pierre Morel <pmorel@xxxxxxxxxxxxx> wrote:
> > >    
> > > > This is the implementation of the VFIO ioctl calls to handle
> > > > the AQIC interception and use GISA to handle interrupts.
> > > >
> > > > Signed-off-by: Pierre Morel <pmorel@xxxxxxxxxxxxx>
> > > > ---
> > > >    drivers/s390/crypto/vfio_ap_ops.c | 95 +++++++++++++++++++++++++++++++
> > > >    1 file changed, 95 insertions(+)
> > > >
> > > > diff --git a/drivers/s390/crypto/vfio_ap_ops.c b/drivers/s390/crypto/vfio_ap_ops.c
> > > > index 272ef427dcc0..f68102163bf4 100644
> > > > --- a/drivers/s390/crypto/vfio_ap_ops.c
> > > > +++ b/drivers/s390/crypto/vfio_ap_ops.c
> > > > @@ -895,12 +895,107 @@ static int vfio_ap_mdev_get_device_info(unsigned long arg)
> > > >    	return copy_to_user((void __user *)arg, &info, minsz);
> > > >    }
> > > >    
> > > > +static int ap_ioctl_setirq(struct ap_matrix_mdev *matrix_mdev,
> > > > +			   struct vfio_ap_aqic *parm)
> > > > +{
> > > > +	struct aqic_gisa aqic_gisa = reg2aqic(0);
> > > > +	struct kvm_s390_gisa *gisa = matrix_mdev->kvm->arch.gisa;
> > > > +	struct ap_status ap_status = reg2status(0);
> > > > +	unsigned long p;
> > > > +	int ret = -1;
> > > > +	int apqn;
> > > > +	uint32_t gd;
> > > > +
> > > > +	apqn = (int)(parm->cmd & 0xffff);
> > >
> > > It seems you always use cmd & 0xffff only. What if there is other stuff
> > > in the remaining bits of cmd? Do you plan to ignore it in any case, or
> > > should you actively check that there is nothing in it?
> > >    
> >
> > I do not think that the ioctl interface should reflect the hardware
> > interface.
> > The ioctl interface ignores the remaining bits.
> > We ignore the FC because we obviously want to make a AQIC FC=3
> > We ignore the T bit.
> >
> > But we receive the information from the intercepting software, i.e. QEMU
> > which should I think do the checks before using the ioctl interface.
>
> Yes, it should; but you still can't know whether it actually did...

I do not care, I just ignore these bits.

> > It seemed easier to me to pass the complete registers and to ignore some
> > bits in them. In case we get any change in the future
> > But we could also only pass the APQN
>
> I'd prefer to use a well-defined structure that explicitly handles the
> userspace<->kernel communication. Not that we start relying on implicit
> assumptions and then things break when userspace does something
> different...

OK, I can pass a u16 in the ioctl parameters and explicitly reserve the 
ignored bits.

Thanks for the review.

Regards,
Pierre

--
Pierre Morel
Linux/KVM/QEMU in BÃblingen - Germany