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

[Pierre Morel <pmorel@linux.vnet.ibm.com>]

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@linux.vnet.ibm.com> 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 <akrowiak@linux.vnet.ibm.com>
>>> ---
>>>   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