Re: [qemu-s390x] [RFC 05/19] s390/zcrypt: base implementation of AP matrix device driver

[Pierre Morel]

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 <address@hidden> wrote:
> >
> > > Introduces a new AP matrix device driver. This device driver
> > > will ultimately perform the following functions:
> > >
> > > * Register with the AP bus to let it know that the matrix
> > >    driver can control AP queue devices. This will allow
> > >    an administrator to unbind an AP queue device from its
> > >    device driver and bind it to the matrix device driver.
> > >    This is how AP queue devices will be reserved for use
> > >    by guest machines.
> > >
> > > * Register the matrix device created by the AP matrix bus
> > >    with the VFIO mediated device framework. This will create
> > >    the sysfs entries needed to create mediated matrix devices.
> > >    Each mediated matrix device can be configured with a matrix
> > >    of adapters, usage domains and control domains that can be
> > >    accessed by a guest machine.
> > >
> > > * Process requests via ioctl calls defined for the mediated
> > >    matrix device. The guest can access the ioctl calls via
> > >    the mediated device's file descriptor to:
> > >
> > >      * Grant access to the adapters, usage domains and
> > >        control domains configured for the mediated matrix
> > >        device.
> > >
> > > This device driver
> > > is built on the VFIO mediated device framework. The VFIO mediated
> > > device framework allows a mediated device to be dedicated exclusively
> > > to a single guest VM.
> > >
> > > Signed-off-by: Tony Krowiak <address@hidden>
> > > ---
> > >   MAINTAINERS                                  |    2 +
> > >   arch/s390/Kconfig                            |   13 +++
> > >   arch/s390/configs/default_defconfig          |    1 +
> > >   arch/s390/configs/gcov_defconfig             |    1 +
> > >   arch/s390/configs/performance_defconfig      |    1 +
> > >   arch/s390/defconfig                          |    1 +
> > >   drivers/s390/crypto/Makefile                 |    6 +-
> > >   drivers/s390/crypto/ap_matrix_bus.c          |    8 ++
> > >   drivers/s390/crypto/ap_matrix_bus.h          |    2 +-
> > >   drivers/s390/crypto/vfio_ap_matrix_drv.c     |  102 
> > > ++++++++++++++++++++++++++
> > >   drivers/s390/crypto/vfio_ap_matrix_private.h |   47 ++++++++++++
> > >   11 files changed, 182 insertions(+), 2 deletions(-)
> > >   create mode 100644 drivers/s390/crypto/vfio_ap_matrix_drv.c
> > >   create mode 100644 drivers/s390/crypto/vfio_ap_matrix_private.h
> > >
> > > 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?

Regards,

Pierre

..snip...

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