linux-kernel - Re: [PATCH v3 05/14] s390: vfio-ap: base implementation of VFIO AP device driver

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Message-Id: <1d5a5e18-1886-dd73-a17e-9bec617507ba@linux.vnet.ibm.com>
Date:   Thu, 15 Mar 2018 14:25:29 +0100
From:   Pierre Morel <pmorel@...ux.vnet.ibm.com>
To:     Tony Krowiak <akrowiak@...ux.vnet.ibm.com>,
        linux-s390@...r.kernel.org, linux-kernel@...r.kernel.org,
        kvm@...r.kernel.org
Cc:     freude@...ibm.com, schwidefsky@...ibm.com,
        heiko.carstens@...ibm.com, borntraeger@...ibm.com,
        cohuck@...hat.com, kwankhede@...dia.com,
        bjsdjshi@...ux.vnet.ibm.com, pbonzini@...hat.com,
        alex.williamson@...hat.com, alifm@...ux.vnet.ibm.com,
        mjrosato@...ux.vnet.ibm.com, jjherne@...ux.vnet.ibm.com,
        thuth@...hat.com, pasic@...ux.vnet.ibm.com, berrange@...hat.com,
        fiuczy@...ux.vnet.ibm.com, buendgen@...ibm.com
Subject: Re: [PATCH v3 05/14] s390: vfio-ap: base implementation of VFIO AP
 device driver

On 14/03/2018 19:25, Tony Krowiak wrote:
> Introduces a new AP device driver. This device driver
> is built on the VFIO mediated device framework. The framework
> provides sysfs interfaces that facilitate passthrough
> access by guests to devices installed on the linux host.
>
> The VFIO AP device driver will serve two purposes:
>
> 1. Provide the interfaces to reserve AP devices for exclusive
>     use by KVM guests. This is accomplished by unbinding the
>     devices to be reserved for guest usage from the default AP
>     device driver and binding them to the VFIO AP device driver.
>
> 2. Implements the functions, callbacks and sysfs attribute
>     interfaces required to create one or more VFIO mediated
>     devices each of which will be used to configure the AP
>     matrix for a guest and serve as a file descriptor
>     for facilitating communication between QEMU and the
>     VFIO AP device driver.
>
> When the VFIO AP device driver is initialized:
>
> * It registers with the AP bus for control of type 10 (CEX4
>    and newer) AP queue devices. The probe and remove callbacks
>    will be provided to support the binding/unbinding of
>    AP queue devices to/from the VFIO AP device driver.
>
> * Creates a /sys/devices/vfio-ap/matrix device to hold
>    the APQNs of the AP devices bound to the VFIO
>    AP device driver and serves as the parent of the
>    mediated devices created for each guest.
>
> Signed-off-by: Tony Krowiak <akrowiak@...ux.vnet.ibm.com>
> ---
>   MAINTAINERS                           |    2 +
>   arch/s390/Kconfig                     |   11 +++
>   drivers/s390/crypto/Makefile          |    4 +
>   drivers/s390/crypto/vfio_ap_drv.c     |  135 +++++++++++++++++++++++++++++++++
>   drivers/s390/crypto/vfio_ap_private.h |   22 ++++++
>   include/uapi/linux/vfio.h             |    2 +
>   6 files changed, 176 insertions(+), 0 deletions(-)
>   create mode 100644 drivers/s390/crypto/vfio_ap_drv.c
>   create mode 100644 drivers/s390/crypto/vfio_ap_private.h
>
> diff --git a/MAINTAINERS b/MAINTAINERS
> index 72742d5..f129253 100644
> --- a/MAINTAINERS
> +++ b/MAINTAINERS
> @@ -11884,6 +11884,8 @@ W:	http://www.ibm.com/developerworks/linux/linux390/
>   S:	Supported
>   F:	arch/s390/include/asm/kvm/kvm-ap.h
>   F:	arch/s390/kvm/kvm-ap.c
> +F:	drivers/s390/crypto/vfio_ap_drv.c
> +F:	drivers/s390/crypto/vfio_ap_private.h
>
>   S390 ZFCP DRIVER
>   M:	Steffen Maier <maier@...ux.vnet.ibm.com>
> diff --git a/arch/s390/Kconfig b/arch/s390/Kconfig
> index cbe1d97..58509db 100644
> --- a/arch/s390/Kconfig
> +++ b/arch/s390/Kconfig
> @@ -771,6 +771,17 @@ config VFIO_CCW
>   	  To compile this driver as a module, choose M here: the
>   	  module will be called vfio_ccw.
>
> +config VFIO_AP
> +	def_tristate m
not sure it must be module by default.
I would not set it by default.
> +	prompt "VFIO support for AP devices"
> +	depends on ZCRYPT && VFIO_MDEV_DEVICE

VFIO_MDEV_DEVICE is a general feature *needed* by VFIO_AP
and has no use case by its own. If it is set it is obviously because some
mediated device drivers needs it.
while ZCRYPT is a Z feature which may be set without VFIO_AP.

So you need:

config VFIO_AP
     def_tristate n
     prompt "VFIO support for AP devices"
     depends on ZCRYPT
     select VFIO_MDEV
     select VFIO_MDEV_DEVICE
...


Pierre

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