Re: [RFC 05/19] s390/zcrypt: base implementation of AP matrix device driver

[Tony Krowiak]

On 11/16/2017 11:47 AM, Cornelia Huck wrote:
> On Thu, 16 Nov 2017 09:25:27 -0500
> Tony Krowiak <akrowiak@xxxxxxxxxxxxxxxxxx> wrote:
>
> > On 11/16/2017 07:35 AM, Cornelia Huck wrote:
> > > On Thu, 16 Nov 2017 13:02:26 +0100
> > > Pierre Morel <pmorel@xxxxxxxxxxxxxxxxxx> wrote:
> > >   
> > > > On 14/11/2017 17:37, Tony Krowiak wrote:
> > > > > On 11/14/2017 07:40 AM, Cornelia Huck wrote:
> > > > > > On Fri, 13 Oct 2017 13:38:50 -0400
> > > > > > Tony Krowiak <akrowiak@xxxxxxxxxxxxxxxxxx> wrote:
> > > > > > > diff --git a/arch/s390/Kconfig b/arch/s390/Kconfig
> > > > > > > index 48af970..411c19a 100644
> > > > > > > --- a/arch/s390/Kconfig
> > > > > > > +++ b/arch/s390/Kconfig
> > > > > > > @@ -722,6 +722,19 @@ config VFIO_CCW
> > > > > > >           To compile this driver as a module, choose M here: the
> > > > > > >           module will be called vfio_ccw.
> > > > > > > +config VFIO_AP_MATRIX
> > > > > > > +    def_tristate m
> > > > > > > +    prompt "Support for Adjunct Processor Matrix device interface"
> > > > > > > +    depends on ZCRYPT
> > > > > > > +    select VFIO
> > > > > > > +    select MDEV
> > > > > > > +    select VFIO_MDEV
> > > > > > > +    select VFIO_MDEV_DEVICE
> > > > > > > +    select IOMMU_API
> > > > > > I think the more common pattern is to depend on the VFIO configs
> > > > > > instead of selecting them.
> > > > > It's ironic because I originally changed from using 'depends on' and
> > > > > changed it based on review comments made
> > > > > on our internal mailing list. I'll go with 'depends on'.
> > > > Is doing like the others a sufficient good reason?
> > > > What if the first who did this did not really think about it?
> > > >
> > > > When an administrator configure the kernel what does he think?
> > > >
> > > > - I want to have AP through AP_VFIO in my guests
> > > > 	and he get implicitly VFIO
> > > > or
> > > > - I want to have VFIO
> > > > 	and he has to explicitly add AP_VFIO too
> > > >
> > > > It seems to me that the first is much more user friendly.
> > > >
> > > > Please tell me if I missed something. dependencies? collateral damages?
> > > > my logic is wrong?
> > > Using select for anything that's not a simple infrastructure dependency
> > > may lead into trouble (we've had issues in the past where options tried
> > > to enable other options but missed dependencies).
> > >
> > > If a user wants to use vfio-ap, I think it is reasonable to expect them
> > > to figure out that they need both ap and vfio for that.
> > >
> > > [And config help has gotten much better than it was years ago; it's not
> > > that hard to figure out what is actually needed.]
> > Is it sufficient to specify 'depends on ZCRYPT && VFIO_MDEV_DEVICE'
> > since 'VFIO_MDEV_DEVICE depends on VFIO && VFIO_MDEV' and 'VFIO_MDEV
> > depends on VFIO' and 'VFIO depends on IOMMU_API'?
> Perhaps ZCRYPT && VFIO_MDEV && VFIO_MDEV_DEVICE, to make it a bit more
> obvious?
Sure, why not.
> [Also, is IOMMU_API only needed to satisfy dependencies?]
Yes, VFIO is dependent upon it.
>