From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mx0b-001b2d01.pphosted.com ([148.163.158.5]:57244 "EHLO mx0b-001b2d01.pphosted.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1727686AbgIOTdr (ORCPT ); Tue, 15 Sep 2020 15:33:47 -0400 Subject: Re: [PATCH v10 04/16] s390/zcrypt: driver callback to indicate resource in use References: <20200821195616.13554-1-akrowiak@linux.ibm.com> <20200821195616.13554-5-akrowiak@linux.ibm.com> <20200914172947.533ddf56.cohuck@redhat.com> From: Tony Krowiak Message-ID: Date: Tue, 15 Sep 2020 15:32:35 -0400 MIME-Version: 1.0 In-Reply-To: <20200914172947.533ddf56.cohuck@redhat.com> Content-Type: text/plain; charset=utf-8; format=flowed Content-Transfer-Encoding: 7bit Content-Language: en-US Sender: linux-s390-owner@vger.kernel.org List-ID: To: Cornelia Huck Cc: linux-s390@vger.kernel.org, linux-kernel@vger.kernel.org, kvm@vger.kernel.org, freude@linux.ibm.com, borntraeger@de.ibm.com, mjrosato@linux.ibm.com, pasic@linux.ibm.com, alex.williamson@redhat.com, kwankhede@nvidia.com, fiuczy@linux.ibm.com, frankja@linux.ibm.com, david@redhat.com, imbrenda@linux.ibm.com, hca@linux.ibm.com, gor@linux.ibm.com, kernel test robot On 9/14/20 11:29 AM, Cornelia Huck wrote: > On Fri, 21 Aug 2020 15:56:04 -0400 > 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. >> >> 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. >> >> Signed-off-by: Tony Krowiak >> Reported-by: kernel test robot > This looks a bit odd... I've removed all of those. These kernel test robot errors were flagged in the last series. The review comments from the robot suggested the reported-by, but I assume that was for patches intended to fix those errors, so I am removing these as per Christian's comments. > >> --- >> drivers/s390/crypto/ap_bus.c | 148 ++++++++++++++++++++++++++++++++--- >> drivers/s390/crypto/ap_bus.h | 4 + >> 2 files changed, 142 insertions(+), 10 deletions(-) >> > (...) > >> @@ -1107,12 +1118,70 @@ 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; >> + >> + /* 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; > ISTR that Christian suggested -EBUSY in a past revision of this series? > I think that would be more appropriate. I went back and looked and sure enough, he did recommend that. You have a great memory! I didn't respond to that comment, so I must have missed it at the time. I personally prefer EADDRINUSE because I think it is more indicative of the reason an AP resource can not be assigned back to the host drivers is because it is in use by a guest or, at the very least, reserved for use by a guest (i.e., assigned to an mdev). To say it is busy implies that the device is busy performing encryption services which may or may not be true at a given moment. Even if so, that is not the reason for refusing to allow reassignment of the device. > > Also, I know we have discussed this before, but it is very hard to > figure out the offending device(s) if the sysfs manipulation failed. Can > we at least drop something into the syslog? That would be far from > perfect, but it gives an admin at least a chance to figure out why they > got an error. Some more structured way that would be usable from tools > can still be added later. I see you found the patch that logged this:) > >> + >> + module_put(drv->owner); >> + >> + return rc; >> +}