[PATCH v16 10/14] s390/zcrypt: driver callback to indicate resource in use

[Tony Krowiak]

Introduces a new driver callback to prevent a root user from unbinding
an AP queue from its device driver if the queue is in use. The callback
will be invoked whenever a change to the AP bus's sysfs apmask or aqmask
attributes would result in one or more AP queues being removed from its
driver. If the callback responds in the affirmative for any driver
queried, the change to the apmask or aqmask will be rejected with a device
busy error.

For this patch, only non-default drivers will be queried. Currently,
there is only one non-default driver, the vfio_ap device driver. The
vfio_ap device driver facilitates pass-through of an AP queue to a
guest. The idea here is that a guest may be administered by a different
sysadmin than the host and we don't want AP resources to unexpectedly
disappear from a guest's AP configuration (i.e., adapters and domains
assigned to the matrix mdev). This will enforce the proper procedure for
removing AP resources intended for guest usage which is to
first unassign them from the matrix mdev, then unbind them from the
vfio_ap device driver.

Signed-off-by: Tony Krowiak <akrowiak@xxxxxxxxxxxxx>
Reviewed-by: Harald Freudenberger <freude@xxxxxxxxxxxxx>
Reviewed-by: Halil Pasic <pasic@xxxxxxxxxxxxx>
---
 drivers/s390/crypto/ap_bus.c | 160 ++++++++++++++++++++++++++++++++---
 drivers/s390/crypto/ap_bus.h |   4 +
 2 files changed, 154 insertions(+), 10 deletions(-)

diff --git a/drivers/s390/crypto/ap_bus.c b/drivers/s390/crypto/ap_bus.c
index 2758d05a802d..b7653cec81ac 100644
--- a/drivers/s390/crypto/ap_bus.c
+++ b/drivers/s390/crypto/ap_bus.c
@@ -36,6 +36,7 @@
 #include <linux/mod_devicetable.h>
 #include <linux/debugfs.h>
 #include <linux/ctype.h>
+#include <linux/module.h>
 
 #include "ap_bus.h"
 #include "ap_debug.h"
@@ -1006,6 +1007,23 @@ static int modify_bitmap(const char *str, unsigned long *bitmap, int bits)
 	return 0;
 }
 
+static int ap_parse_bitmap_str(const char *str, unsigned long *bitmap, int bits,
+			       unsigned long *newmap)
+{
+	unsigned long size;
+	int rc;
+
+	size = BITS_TO_LONGS(bits) * sizeof(unsigned long);
+	if (*str == '+' || *str == '-') {
+		memcpy(newmap, bitmap, size);
+		rc = modify_bitmap(str, newmap, bits);
+	} else {
+		memset(newmap, 0, size);
+		rc = hex2bitmap(str, newmap, bits);
+	}
+	return rc;
+}
+
 int ap_parse_mask_str(const char *str,
 		      unsigned long *bitmap, int bits,
 		      struct mutex *lock)
@@ -1025,14 +1043,7 @@ int ap_parse_mask_str(const char *str,
 		kfree(newmap);
 		return -ERESTARTSYS;
 	}
-
-	if (*str == '+' || *str == '-') {
-		memcpy(newmap, bitmap, size);
-		rc = modify_bitmap(str, newmap, bits);
-	} else {
-		memset(newmap, 0, size);
-		rc = hex2bitmap(str, newmap, bits);
-	}
+	rc = ap_parse_bitmap_str(str, bitmap, bits, newmap);
 	if (rc == 0)
 		memcpy(bitmap, newmap, size);
 	mutex_unlock(lock);
@@ -1224,12 +1235,76 @@ static ssize_t apmask_show(struct bus_type *bus, char *buf)
 	return rc;
 }
 
+static int __verify_card_reservations(struct device_driver *drv, void *data)
+{
+	int rc = 0;
+	struct ap_driver *ap_drv = to_ap_drv(drv);
+	unsigned long *newapm = (unsigned long *)data;
+
+	/*
+	 * No need to verify whether the driver is using the queues if it is the
+	 * default driver.
+	 */
+	if (ap_drv->flags & AP_DRIVER_FLAG_DEFAULT)
+		return 0;
+
+	/*
+	 * increase the driver's module refcounter to be sure it is not
+	 * going away when we invoke the callback function.
+	 */
+	if (!try_module_get(drv->owner))
+		return 0;
+
+	if (ap_drv->in_use) {
+		rc = ap_drv->in_use(newapm, ap_perms.aqm);
+		if (rc)
+			rc = -EBUSY;
+	}
+
+	/* release the driver's module */
+	module_put(drv->owner);
+
+	return rc;
+}
+
+static int apmask_commit(unsigned long *newapm)
+{
+	int rc;
+	unsigned long reserved[BITS_TO_LONGS(AP_DEVICES)];
+
+	/*
+	 * Check if any bits in the apmask have been set which will
+	 * result in queues being removed from non-default drivers
+	 */
+	if (bitmap_andnot(reserved, newapm, ap_perms.apm, AP_DEVICES)) {
+		rc = bus_for_each_drv(&ap_bus_type, NULL, reserved,
+				      __verify_card_reservations);
+		if (rc)
+			return rc;
+	}
+
+	memcpy(ap_perms.apm, newapm, APMASKSIZE);
+
+	return 0;
+}
+
 static ssize_t apmask_store(struct bus_type *bus, const char *buf,
 			    size_t count)
 {
 	int rc;
+	DECLARE_BITMAP(newapm, AP_DEVICES);
+
+	if (mutex_lock_interruptible(&ap_perms_mutex))
+		return -ERESTARTSYS;
 
-	rc = ap_parse_mask_str(buf, ap_perms.apm, AP_DEVICES, &ap_perms_mutex);
+	rc = ap_parse_bitmap_str(buf, ap_perms.apm, AP_DEVICES, newapm);
+	if (rc)
+		goto done;
+
+	rc = apmask_commit(newapm);
+
+done:
+	mutex_unlock(&ap_perms_mutex);
 	if (rc)
 		return rc;
 
@@ -1255,12 +1330,77 @@ static ssize_t aqmask_show(struct bus_type *bus, char *buf)
 	return rc;
 }
 
+static int __verify_queue_reservations(struct device_driver *drv, void *data)
+{
+	int rc = 0;
+	struct ap_driver *ap_drv = to_ap_drv(drv);
+	unsigned long *newaqm = (unsigned long *)data;
+
+	/*
+	 * If the reserved bits do not identify queues reserved for use by the
+	 * non-default driver, there is no need to verify the driver is using
+	 * the queues.
+	 */
+	if (ap_drv->flags & AP_DRIVER_FLAG_DEFAULT)
+		return 0;
+
+	/*
+	 * increase the driver's module refcounter to be sure it is not
+	 * going away when we invoke the callback function.
+	 */
+	if (!try_module_get(drv->owner))
+		return 0;
+
+	if (ap_drv->in_use) {
+		rc = ap_drv->in_use(ap_perms.apm, newaqm);
+		if (rc)
+			return -EBUSY;
+	}
+
+	/* release the driver's module */
+	module_put(drv->owner);
+
+	return rc;
+}
+
+static int aqmask_commit(unsigned long *newaqm)
+{
+	int rc;
+	unsigned long reserved[BITS_TO_LONGS(AP_DOMAINS)];
+
+	/*
+	 * Check if any bits in the aqmask have been set which will
+	 * result in queues being removed from non-default drivers
+	 */
+	if (bitmap_andnot(reserved, newaqm, ap_perms.aqm, AP_DOMAINS)) {
+		rc = bus_for_each_drv(&ap_bus_type, NULL, reserved,
+				      __verify_queue_reservations);
+		if (rc)
+			return rc;
+	}
+
+	memcpy(ap_perms.aqm, newaqm, AQMASKSIZE);
+
+	return 0;
+}
+
 static ssize_t aqmask_store(struct bus_type *bus, const char *buf,
 			    size_t count)
 {
 	int rc;
+	DECLARE_BITMAP(newaqm, AP_DOMAINS);
+
+	if (mutex_lock_interruptible(&ap_perms_mutex))
+		return -ERESTARTSYS;
+
+	rc = ap_parse_bitmap_str(buf, ap_perms.aqm, AP_DOMAINS, newaqm);
+	if (rc)
+		goto done;
+
+	rc = aqmask_commit(newaqm);
 
-	rc = ap_parse_mask_str(buf, ap_perms.aqm, AP_DOMAINS, &ap_perms_mutex);
+done:
+	mutex_unlock(&ap_perms_mutex);
 	if (rc)
 		return rc;
 
diff --git a/drivers/s390/crypto/ap_bus.h b/drivers/s390/crypto/ap_bus.h
index 472efd3a755c..95c9da072f81 100644
--- a/drivers/s390/crypto/ap_bus.h
+++ b/drivers/s390/crypto/ap_bus.h
@@ -145,6 +145,7 @@ struct ap_driver {
 
 	int (*probe)(struct ap_device *);
 	void (*remove)(struct ap_device *);
+	int (*in_use)(unsigned long *apm, unsigned long *aqm);
 };
 
 #define to_ap_drv(x) container_of((x), struct ap_driver, driver)
@@ -293,6 +294,9 @@ void ap_queue_init_state(struct ap_queue *aq);
 struct ap_card *ap_card_create(int id, int queue_depth, int raw_device_type,
 			       int comp_device_type, unsigned int functions);
 
+#define APMASKSIZE (BITS_TO_LONGS(AP_DEVICES) * sizeof(unsigned long))
+#define AQMASKSIZE (BITS_TO_LONGS(AP_DOMAINS) * sizeof(unsigned long))
+
 struct ap_perms {
 	unsigned long ioctlm[BITS_TO_LONGS(AP_IOCTLS)];
 	unsigned long apm[BITS_TO_LONGS(AP_DEVICES)];
-- 
2.30.2