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SubjectRe: [PATCH v9 09/22] s390: vfio-ap: register matrix device with VFIO mdev framework
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On 08/14/2018 07:19 AM, Cornelia Huck wrote:
> On Mon, 13 Aug 2018 17:48:06 -0400
> Tony Krowiak <akrowiak@linux.vnet.ibm.com> wrote:
>
>> From: Tony Krowiak <akrowiak@linux.ibm.com>
>>
>> Registers the matrix device created by the VFIO AP device
>> driver with the VFIO mediated device framework.
>> Registering the matrix device will create the sysfs
>> structures needed to create mediated matrix devices
>> each of which will be used to configure the AP matrix
>> for a guest and connect it to the VFIO AP device driver.
>>
>> Registering the matrix device with the VFIO mediated device
>> framework will create the following sysfs structures:
>>
>> /sys/devices/vfio_ap/matrix/
>> ...... [mdev_supported_types]
>> ......... [vfio_ap-passthrough]
>> ............ create
>>
>> To create a mediated device for the AP matrix device, write a UUID
>> to the create file:
>>
>> uuidgen > create
>>
>> A symbolic link to the mediated device's directory will be created in the
>> devices subdirectory named after the generated $uuid:
>>
>> /sys/devices/vfio_ap/matrix/
>> ...... [mdev_supported_types]
>> ......... [vfio_ap-passthrough]
>> ............ [devices]
>> ............... [$uuid]
>>
>> A symbolic link to the mediated device will also be created
>> in the vfio_ap matrix's directory:
>>
>> /sys/devices/vfio_ap/matrix/[$uuid]
>>
>> Signed-off-by: Tony Krowiak <akrowiak@linux.ibm.com>
>> Reviewed-by: Halil Pasic <pasic@linux.ibm.com>
>> Tested-by: Michael Mueller <mimu@linux.ibm.com>
>> Tested-by: Farhan Ali <alifm@linux.ibm.com>
>> Signed-off-by: Christian Borntraeger <borntraeger@de.ibm.com>
>> ---
>> MAINTAINERS | 1 +
>> drivers/s390/crypto/Makefile | 2 +-
>> drivers/s390/crypto/vfio_ap_drv.c | 23 ++++++
>> drivers/s390/crypto/vfio_ap_ops.c | 124 +++++++++++++++++++++++++++++++++
>> drivers/s390/crypto/vfio_ap_private.h | 45 ++++++++++++
>> include/uapi/linux/vfio.h | 1 +
>> 6 files changed, 195 insertions(+), 1 deletions(-)
>> create mode 100644 drivers/s390/crypto/vfio_ap_ops.c
>>
>
>> diff --git a/drivers/s390/crypto/vfio_ap_ops.c b/drivers/s390/crypto/vfio_ap_ops.c
>> new file mode 100644
>> index 0000000..8018c2d
>> --- /dev/null
>> +++ b/drivers/s390/crypto/vfio_ap_ops.c
>> @@ -0,0 +1,124 @@
>> +// SPDX-License-Identifier: GPL-2.0+
>> +/*
>> + * Adjunct processor matrix VFIO device driver callbacks.
>> + *
>> + * Copyright IBM Corp. 2018
>> + *
>> + * Author(s): Tony Krowiak <akrowiak@linux.ibm.com>
>> + * Halil Pasic <pasic@linux.ibm.com>
>> + * Pierre Morel <pmorel@linux.ibm.com>
>> + */
>> +#include <linux/string.h>
>> +#include <linux/vfio.h>
>> +#include <linux/device.h>
>> +#include <linux/list.h>
>> +#include <linux/ctype.h>
>> +
>> +#include "vfio_ap_private.h"
>> +
>> +#define VFIO_AP_MDEV_TYPE_HWVIRT "passthrough"
>> +#define VFIO_AP_MDEV_NAME_HWVIRT "VFIO AP Passthrough Device"
>> +
>> +static void vfio_ap_matrix_init(struct ap_config_info *info,
>> + struct ap_matrix *matrix)
>> +{
>> + matrix->apm_max = info->apxa ? info->Na : 63;
>> + matrix->aqm_max = info->apxa ? info->Nd : 15;
>> + matrix->adm_max = info->apxa ? info->Nd : 15;
>> +}
>> +
>> +static int vfio_ap_mdev_create(struct kobject *kobj, struct mdev_device *mdev)
>> +{
>> + struct ap_matrix_mdev *matrix_mdev;
>> +
>> + matrix_mdev = kzalloc(sizeof(*matrix_mdev), GFP_KERNEL);
>> + if (!matrix_mdev)
>> + return -ENOMEM;
>> +
>> + matrix_mdev->name = dev_name(mdev_dev(mdev));
>> + vfio_ap_matrix_init(&matrix_dev.info, &matrix_mdev->matrix);
>> + mdev_set_drvdata(mdev, matrix_mdev);
>> +
>> + if (atomic_dec_if_positive(&matrix_dev.available_instances) < 0) {
>> + kfree(matrix_mdev);
>> + return -EPERM;
>> + }
> Maybe move this check to the top of the function?

Please ignore my previous response to your comment. I can't move the call to
atomic_dec_if_positive() to the top of the function because it
decrements the
available_instances and if the kzalloc() of matrix_mdev fails, then the
value
would have to then be incremented to remain valid. What I can do is this:

1. Check the value of available_instances using atomic_read() at the top of
the function and if it is zero, return an error.

2. Replace the call to atomic_dec_if_positive() with a call to atomic_dec()
to decrement the available_instances.

I agree that it makes sense to return before attempting to allocate the
matrix_mdev if available_instances is zero.

>
>> +
>> + mutex_lock(&matrix_dev.lock);
>> + list_add(&matrix_mdev->list, &matrix_dev.mdev_list);
>> + mutex_unlock(&matrix_dev.lock);
>> +
>> + return 0;
>> +}


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