[PATCH] s390/vfio-ap: Driver feature advertisement

Jason J. Herne
2024-09-05T12:43:56Z

Advertise features of the driver for the benefit of automated tooling
like Libvirt and mdevctl.

Signed-off-by: Jason J. Herne <jjherne@linux.ibm.com>
Reviewed-by: Anthony Krowiak <akrowiak@linux.ibm.com>
---
Documentation/arch/s390/vfio-ap.rst | 34 +++++++++++++++++++++++++++++
drivers/s390/crypto/vfio_ap_drv.c | 13 +++++++++++
2 files changed, 47 insertions(+)

diff --git a/Documentation/arch/s390/vfio-ap.rst b/Documentation/arch/s390/vfio-ap.rst
index ea744cbc8687..22f1965af500 100644
--- a/Documentation/arch/s390/vfio-ap.rst
+++ b/Documentation/arch/s390/vfio-ap.rst
@@ -999,6 +999,40 @@ the vfio_ap mediated device to which it is assigned as long as each new APQN
resulting from plugging it in references a queue device bound to the vfio_ap
device driver.

+Driver Features
+===============
+The vfio_ap driver exposes a sysfs file containing supported features.
+This exists so third party tools (like Libvirt and mdevctl) can query the
+availability of specific features.
+
+The features list can be found here: /sys/bus/matrix/devices/matrix/features
+
+Entries are \n delimited. Each entry contains a key value pair. The key is made
+up of a combination of alphanumeric and underscore characters. The separator
+consists of a space, a colon and then another space. The value consists of
+alphanumeric, space, and underscore characters.
+
+Example:
+cat /sys/bus/matrix/devices/matrix/features
+flags : guest_matrix dyn ap_config
+
+Presently only a single field named flags is defined. It is meant to advertise a
+list of features the driver provides. The flags fields advertises the following
+features:
+
+---------------+---------------------------------------------------------------+
+| Flag | Description |
++==============+===============================================================+
+| guest_matrix | guest_matrix attribute exists. It reports the matrix of |
+| | adapters and domains that are or will be passed through to a |
+| | guest when the mdev is attached to it. |
++--------------+---------------------------------------------------------------+
+| hotplug | Indicates hot plug/unplug of AP adapters, domains and control |
+| | domains for a guest to which the mdev is attached. |
++------------+-----------------------------------------------------------------+
+| ap_config | ap_config interface for one-shot modifications to mdev config |
++--------------+---------------------------------------------------------------+
+
Limitations
===========
Live guest migration is not supported for guests using AP devices without
diff --git a/drivers/s390/crypto/vfio_ap_drv.c b/drivers/s390/crypto/vfio_ap_drv.c
index 4aeb3e1213c7..85b8094f5e69 100644
--- a/drivers/s390/crypto/vfio_ap_drv.c
+++ b/drivers/s390/crypto/vfio_ap_drv.c
@@ -26,6 +26,18 @@ MODULE_LICENSE("GPL v2");
struct ap_matrix_dev *matrix_dev;
debug_info_t *vfio_ap_dbf_info;

+static ssize_t features_show(struct device *dev, struct device_attribute *attr, char *buf)
+{
+ return sprintf(buf, "flags : guest_matrix hotplug ap_config\n");
+}
+static DEVICE_ATTR_RO(features);
+
+static struct attribute *matrix_dev_attrs[] = {
+ &dev_attr_features.attr,
+ NULL,
+};
+ATTRIBUTE_GROUPS(matrix_dev);
+
/* Only type 10 adapters (CEX4 and later) are supported
* by the AP matrix device driver
*/
@@ -68,6 +80,7 @@ static struct device_driver matrix_driver = {
.name = "vfio_ap",
.bus = &matrix_bus,
.suppress_bind_attrs = true,
+ .dev_groups = matrix_dev_groups,
};

static int vfio_ap_matrix_dev_create(void)
--
2.46.0