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

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Date:   Tue, 22 Dec 2020 05:05:21 +0100
From:   Halil Pasic <pasic@...ux.ibm.com>
To:     Tony Krowiak <akrowiak@...ux.ibm.com>
Cc:     linux-s390@...r.kernel.org, linux-kernel@...r.kernel.org,
        kvm@...r.kernel.org, stable@...r.kernel.org,
        borntraeger@...ibm.com, cohuck@...hat.com, kwankhede@...dia.com,
        pbonzini@...hat.com, alex.williamson@...hat.com,
        pasic@...ux.vnet.ibm.com
Subject: Re: [PATCH v4] s390/vfio-ap: clean up vfio_ap resources when KVM
 pointer invalidated

On Mon, 21 Dec 2020 13:56:25 -0500
Tony Krowiak <akrowiak@...ux.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@...r.kernel.org
> Signed-off-by: Tony Krowiak <akrowiak@...ux.ibm.com>
> Reviewed-by: Halil Pasic <pasic@...ux.ibm.com>
> Reviewed-by: Cornelia Huck <cohuck@...hat.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?

Otherwise LGTM!

Regards,
Halil

> +notify_done:
> +	mutex_unlock(&matrix_dev->lock);
> +	return notify_rc;
>  }
> 

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