Re: [PATCH v1] s390/vfio-ap: Signal eventfd when guest AP configuration is changed

[Harald Freudenberger <freude@linux.ibm.com>]

On 2025-01-07 19:36, Rorie Reyes wrote:
> In this patch, an eventfd object is created by the vfio_ap device 
> driver
> and used to notify userspace when a guests's AP configuration is
> dynamically changed. Such changes may occur whenever:
> 
> * An adapter, domain or control domain is assigned to or unassigned 
> from a
>   mediated device that is attached to the guest.
> * A queue assigned to the mediated device that is attached to a guest 
> is
>   bound to or unbound from the vfio_ap device driver. This can occur
>   either by manually binding/unbinding the queue via the vfio_ap 
> driver's
>   sysfs bind/unbind attribute interfaces, or because an adapter, domain 
> or
>   control domain assigned to the mediated device is added to or removed
>   from the host's AP configuration via an SE/HMC
> 
> The purpose of this patch is to provide immediate notification of 
> changes
> made to a guest's AP configuration by the vfio_ap driver. This will 
> enable
> the guest to take immediate action rather than relying on polling or 
> some
> other inefficient mechanism to detect changes to its AP configuration.
> 
> Note that there are corresponding QEMU patches that will be shipped 
> along
> with this patch (see vfio-ap: Report vfio-ap configuration changes) 
> that
> will pick up the eventfd signal.
> 
> Signed-off-by: Rorie Reyes <rreyes@linux.ibm.com>
> Reviewed-by: Anthony Krowiak <akrowiak@linux.ibm.com>
> Tested-by: Anthony Krowiak <akrowiak@linux.ibm.com>
> ---
>  drivers/s390/crypto/vfio_ap_ops.c     | 52 ++++++++++++++++++++++++++-
>  drivers/s390/crypto/vfio_ap_private.h |  2 ++
>  include/uapi/linux/vfio.h             |  1 +
>  3 files changed, 54 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/s390/crypto/vfio_ap_ops.c
> b/drivers/s390/crypto/vfio_ap_ops.c
> index a52c2690933f..c6ff4ab13f16 100644
> --- a/drivers/s390/crypto/vfio_ap_ops.c
> +++ b/drivers/s390/crypto/vfio_ap_ops.c
> @@ -650,13 +650,22 @@ static void vfio_ap_matrix_init(struct
> ap_config_info *info,
>  	matrix->adm_max = info->apxa ? info->nd : 15;
>  }
> 
> +static void signal_guest_ap_cfg_changed(struct ap_matrix_mdev 
> *matrix_mdev)
> +{
> +		if (matrix_mdev->cfg_chg_trigger)
> +			eventfd_signal(matrix_mdev->cfg_chg_trigger);
> +}
> +
>  static void vfio_ap_mdev_update_guest_apcb(struct ap_matrix_mdev 
> *matrix_mdev)
>  {
> -	if (matrix_mdev->kvm)
> +	if (matrix_mdev->kvm) {
>  		kvm_arch_crypto_set_masks(matrix_mdev->kvm,
>  					  matrix_mdev->shadow_apcb.apm,
>  					  matrix_mdev->shadow_apcb.aqm,
>  					  matrix_mdev->shadow_apcb.adm);
> +
> +		signal_guest_ap_cfg_changed(matrix_mdev);
> +	}
>  }
> 
>  static bool vfio_ap_mdev_filter_cdoms(struct ap_matrix_mdev 
> *matrix_mdev)
> @@ -792,6 +801,7 @@ static int vfio_ap_mdev_probe(struct mdev_device 
> *mdev)
>  	if (ret)
>  		goto err_put_vdev;
>  	matrix_mdev->req_trigger = NULL;
> +	matrix_mdev->cfg_chg_trigger = NULL;
>  	dev_set_drvdata(&mdev->dev, matrix_mdev);
>  	mutex_lock(&matrix_dev->mdevs_lock);
>  	list_add(&matrix_mdev->node, &matrix_dev->mdev_list);
> @@ -1860,6 +1870,7 @@ static void vfio_ap_mdev_unset_kvm(struct
> ap_matrix_mdev *matrix_mdev)
>  		get_update_locks_for_kvm(kvm);
> 
>  		kvm_arch_crypto_clear_masks(kvm);
> +		signal_guest_ap_cfg_changed(matrix_mdev);
>  		vfio_ap_mdev_reset_queues(matrix_mdev);
>  		kvm_put_kvm(kvm);
>  		matrix_mdev->kvm = NULL;
> @@ -2097,6 +2108,10 @@ static ssize_t vfio_ap_get_irq_info(unsigned 
> long arg)
>  		info.count = 1;
>  		info.flags = VFIO_IRQ_INFO_EVENTFD;
>  		break;
> +	case VFIO_AP_CFG_CHG_IRQ_INDEX:
> +		info.count = 1;
> +		info.flags = VFIO_IRQ_INFO_EVENTFD;
> +		break;
>  	default:
>  		return -EINVAL;
>  	}
> @@ -2160,6 +2175,39 @@ static int vfio_ap_set_request_irq(struct
> ap_matrix_mdev *matrix_mdev,
>  	return 0;
>  }
> 
> +static int vfio_ap_set_cfg_change_irq(struct ap_matrix_mdev
> *matrix_mdev, unsigned long arg)
> +{
> +	s32 fd;
> +	void __user *data;
> +	unsigned long minsz;
> +	struct eventfd_ctx *cfg_chg_trigger;
> +
> +	minsz = offsetofend(struct vfio_irq_set, count);
> +	data = (void __user *)(arg + minsz);
> +
> +	if (get_user(fd, (s32 __user *)data))
> +		return -EFAULT;
> +
> +	if (fd == -1) {
> +		if (matrix_mdev->cfg_chg_trigger)
> +			eventfd_ctx_put(matrix_mdev->cfg_chg_trigger);
> +		matrix_mdev->cfg_chg_trigger = NULL;
> +	} else if (fd >= 0) {
> +		cfg_chg_trigger = eventfd_ctx_fdget(fd);
> +		if (IS_ERR(cfg_chg_trigger))
> +			return PTR_ERR(cfg_chg_trigger);
> +
> +		if (matrix_mdev->cfg_chg_trigger)
> +			eventfd_ctx_put(matrix_mdev->cfg_chg_trigger);
> +
> +		matrix_mdev->cfg_chg_trigger = cfg_chg_trigger;
> +	} else {
> +		return -EINVAL;
> +	}
> +
> +	return 0;
> +}
> +
>  static int vfio_ap_set_irqs(struct ap_matrix_mdev *matrix_mdev,
>  			    unsigned long arg)
>  {
> @@ -2175,6 +2223,8 @@ static int vfio_ap_set_irqs(struct
> ap_matrix_mdev *matrix_mdev,
>  		switch (irq_set.index) {
>  		case VFIO_AP_REQ_IRQ_INDEX:
>  			return vfio_ap_set_request_irq(matrix_mdev, arg);
> +		case VFIO_AP_CFG_CHG_IRQ_INDEX:
> +			return vfio_ap_set_cfg_change_irq(matrix_mdev, arg);
>  		default:
>  			return -EINVAL;
>  		}
> diff --git a/drivers/s390/crypto/vfio_ap_private.h
> b/drivers/s390/crypto/vfio_ap_private.h
> index 437a161c8659..37de9c69b6eb 100644
> --- a/drivers/s390/crypto/vfio_ap_private.h
> +++ b/drivers/s390/crypto/vfio_ap_private.h
> @@ -105,6 +105,7 @@ struct ap_queue_table {
>   * @mdev:	the mediated device
>   * @qtable:	table of queues (struct vfio_ap_queue) assigned to the 
> mdev
>   * @req_trigger eventfd ctx for signaling userspace to return a device
> + * @cfg_chg_trigger eventfd ctx to signal AP config changed to 
> userspace
>   * @apm_add:	bitmap of APIDs added to the host's AP configuration
>   * @aqm_add:	bitmap of APQIs added to the host's AP configuration
>   * @adm_add:	bitmap of control domain numbers added to the host's AP
> @@ -120,6 +121,7 @@ struct ap_matrix_mdev {
>  	struct mdev_device *mdev;
>  	struct ap_queue_table qtable;
>  	struct eventfd_ctx *req_trigger;
> +	struct eventfd_ctx *cfg_chg_trigger;
>  	DECLARE_BITMAP(apm_add, AP_DEVICES);
>  	DECLARE_BITMAP(aqm_add, AP_DOMAINS);
>  	DECLARE_BITMAP(adm_add, AP_DOMAINS);
> diff --git a/include/uapi/linux/vfio.h b/include/uapi/linux/vfio.h
> index c8dbf8219c4f..a2d3e1ac6239 100644
> --- a/include/uapi/linux/vfio.h
> +++ b/include/uapi/linux/vfio.h
> @@ -671,6 +671,7 @@ enum {
>   */
>  enum {
>  	VFIO_AP_REQ_IRQ_INDEX,
> +	VFIO_AP_CFG_CHG_IRQ_INDEX,
>  	VFIO_AP_NUM_IRQS
>  };

Rorie, this is to inform listeners on the host of the guest.
The guest itself already sees this "inside" with uevents triggered
by the AP bus code.

Do you have a consumer for these events?