Re: [PATCH v4] s390/vfio-ap: clean up vfio_ap resources when KVM pointer invalidated

Tony Krowiak
2020-12-22T15:37:49Z

On 12/21/20 11:05 PM, Halil Pasic wrote:
> On Mon, 21 Dec 2020 13:56:25 -0500
> Tony Krowiak <akrowiak@linux.ibm.com> wrote:
>
>> The vfio_ap device driver registers a group notifier with VFIO when the
>> file descriptor for a VFIO mediated device for a KVM guest is opened to
>> receive notification that the KVM pointer is set (VFIO_GROUP_NOTIFY_SET_KVM
>> event). When the KVM pointer is set, the vfio_ap driver takes the
>> following actions:
>> 1. Stashes the KVM pointer in the vfio_ap_mdev struct that holds the state
>> of the mediated device.
>> 2. Calls the kvm_get_kvm() function to increment its reference counter.
>> 3. Sets the function pointer to the function that handles interception of
>> the instruction that enables/disables interrupt processing.
>> 4. Sets the masks in the KVM guest's CRYCB to pass AP resources through to
>> the guest.
>>
>> In order to avoid memory leaks, when the notifier is called to receive
>> notification that the KVM pointer has been set to NULL, the vfio_ap device
>> driver should reverse the actions taken when the KVM pointer was set.
>>
>> Fixes: 258287c994de ("s390: vfio-ap: implement mediated device open callback")
>> Cc: stable@vger.kernel.org
>> Signed-off-by: Tony Krowiak <akrowiak@linux.ibm.com>
>> Reviewed-by: Halil Pasic <pasic@linux.ibm.com>
>> Reviewed-by: Cornelia Huck <cohuck@redhat.com>
> [..]
>
>> static int vfio_ap_mdev_group_notifier(struct notifier_block *nb,
>> unsigned long action, void *data)
>> {
>> - int ret;
>> + int ret, notify_rc = NOTIFY_DONE;
>> struct ap_matrix_mdev *matrix_mdev;
>>
>> if (action != VFIO_GROUP_NOTIFY_SET_KVM)
>> return NOTIFY_OK;
>>
>> matrix_mdev = container_of(nb, struct ap_matrix_mdev, group_notifier);
>> + mutex_lock(&matrix_dev->lock);
>>
>> if (!data) {
>> - matrix_mdev->kvm = NULL;
>> - return NOTIFY_OK;
>> + if (matrix_mdev->kvm)
>> + vfio_ap_mdev_unset_kvm(matrix_mdev);
>> + notify_rc = NOTIFY_OK;
>> + goto notify_done;
>> }
>>
>> ret = vfio_ap_mdev_set_kvm(matrix_mdev, data);
>> if (ret)
>> - return NOTIFY_DONE;
>> + goto notify_done;
>>
>> /* If there is no CRYCB pointer, then we can't copy the masks */
>> if (!matrix_mdev->kvm->arch.crypto.crycbd)
>> - return NOTIFY_DONE;
>> + goto notify_done;
>>
>> kvm_arch_crypto_set_masks(matrix_mdev->kvm, matrix_mdev->matrix.apm,
>> matrix_mdev->matrix.aqm,
>> matrix_mdev->matrix.adm);
>>
>> - return NOTIFY_OK;
> Shouldn't there be an
> + notify_rc = NOTIFY_OK;
> here? I mean you initialize notify_rc to NOTIFY_DONE, in the !data branch
> on success you set notify_rc to NOTIFY_OK, but in the !!data branch it
> just stays NOTIFY_DONE. Or am I missing something?

I don't think it matters much since NOTIFY_OK and NOTIFY_DONE have
no further effect on processing of the notification queue, but I believe
you are correct, this is a change from what we originally had. I can
restore the original return values if you'd prefer.

>
> Otherwise LGTM!
>
> Regards,
> Halil
>
>> +notify_done:
>> + mutex_unlock(&matrix_dev->lock);
>> + return notify_rc;
>> }
>>
> [..]