On 4/14/20 8:08 AM, Cornelia Huck wrote:
On Tue, 7 Apr 2020 15:20:03 -0400
Tony Krowiak <akrowiak@xxxxxxxxxxxxx> wrote:
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 intent of
this callback is to provide a driver with the means to prevent a root user
from inadvertently taking a queue away from a guest and giving it to the
host while the guest is still using it. 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
in use 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 manages AP queues passed through to one or more
guests and we don't want to unexpectedly take AP resources away from
guests which are most likely independently administered.
Signed-off-by: Tony Krowiak <akrowiak@xxxxxxxxxxxxx>
---
drivers/s390/crypto/ap_bus.c | 144 +++++++++++++++++++++++++++++++++--
drivers/s390/crypto/ap_bus.h | 4 +
2 files changed, 142 insertions(+), 6 deletions(-)
diff --git a/drivers/s390/crypto/ap_bus.c b/drivers/s390/crypto/ap_bus.c
index 5256e3ce84e5..af15c095e76a 100644
--- a/drivers/s390/crypto/ap_bus.c
+++ b/drivers/s390/crypto/ap_bus.c
@@ -35,6 +35,7 @@
#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"
@@ -995,9 +996,11 @@ int ap_parse_mask_str(const char *str,
newmap = kmalloc(size, GFP_KERNEL);
if (!newmap)
return -ENOMEM;
- if (mutex_lock_interruptible(lock)) {
- kfree(newmap);
- return -ERESTARTSYS;
+ if (lock) {
+ if (mutex_lock_interruptible(lock)) {
+ kfree(newmap);
+ return -ERESTARTSYS;
+ }
This whole function is a bit odd. It seems all masks we want to
manipulate are always guarded by the ap_perms_mutex, and the need for
allowing lock == NULL comes from wanting to call this function with the
ap_perms_mutex already held.
That would argue for a locked/unlocked version of this function... but
looking at it, why do we lock the way we do? The one thing this
function (prior to this patch) does outside of the holding of the mutex
is the allocation and freeing of newmap. But with this patch, we do the
allocation and freeing of newmap while holding the mutex. Something
seems a bit weird here.
Note that the ap_parse_mask function copies the newmap
to the bitmap passed in as a parameter to the function.
Prior to the introduction of this patch, the calling functions - i.e.,
apmask_store(), aqmask_store() and ap_perms_init() - passed
in the actual bitmap (i.e., ap_perms.apm or ap_perms aqm),
so the ap_perms were changed directly by this function.
With this patch, the apmask_store() and aqmask_store()
functions now pass in a copy of those bitmaps. This is so
we can verify that any APQNs being removed are not
in use by the vfio_ap device driver before committing the
change to ap_perms. Consequently, it is now necessary
to take the lock for the until the changes are committed.
Having explained that, you make a valid argument that
this calls for a locked/unlocked version of this function, so
I will modify this patch to that effect.
}
if (*str == '+' || *str == '-') {
