Re: [PATCH v8 04/16] s390/zcrypt: driver callback to indicate resource in use

Christian Borntraeger
2020-07-08T12:27:27Z

On 05.06.20 23:39, Tony Krowiak 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 matrix mdev and giving it to
> the host while it is assigned to the matrix mdev. 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.

The alternative would be to tear down the connection in the matrix mdev in this
callback (so that the guest will see a hot unplug), but actually making this
a more conscious decision (requiring 2 steps from the host admin) is certainly
also fine.

>
> 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, domains and
> control 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.

What I said above, we can force a hot unplug to the guest, but we require
to do 2 steps. I think this is fine.

>
> Signed-off-by: Tony Krowiak <akrowiak@linux.ibm.com>
> ---
> drivers/s390/crypto/ap_bus.c | 148 ++++++++++++++++++++++++++++++++---
> drivers/s390/crypto/ap_bus.h | 4 +
> 2 files changed, 142 insertions(+), 10 deletions(-)
>
> diff --git a/drivers/s390/crypto/ap_bus.c b/drivers/s390/crypto/ap_bus.c
> index e71ca4a719a5..40cb5861dad3 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"
> @@ -876,6 +877,23 @@ 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); ^ ^ spaces around the *
> + 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)
> @@ -895,14 +913,7 @@ int ap_parse_mask_str(const char *str,
> kfree(newmap);
> return -ERESTARTSYS;
> }
> -
> - if (*str == '+' || *str == '-') {
> - memcpy(newmap, bitmap, size);

Do we still need the size variable in here?

> - 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);
> @@ -1092,12 +1103,70 @@ static ssize_t apmask_show(struct bus_type *bus, char *buf)
> return rc;
> }
>
> +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;
> +
> + /* The non-default driver's module must be loaded */> + if (!try_module_get(drv->owner))
> + return 0;
> +
> + if (ap_drv->in_use)
> + if (ap_drv->in_use(newapm, ap_perms.aqm))
> + rc = -EADDRINUSE;

I think -EBUSY is more appropriate. (also in the other places)