Re: [Qemu-devel] [PATCH v5 4/6] s390x/vfio: ap: Introduce VFIO AP device

[Halil Pasic <pasic@linux.ibm.com>]

On 05/08/2018 02:25 PM, Tony Krowiak wrote:
> Introduces a VFIO based AP device. The device is defined via
> the QEMU command line by specifying:
> 
>      -device vfio-ap,sysfsdev=<path-to-mediated-matrix-device>
> 
> There may be only one vfio-ap device configured for a guest.
> 
> The mediated matrix device is created by the VFIO AP device
[..]
> + * directory.
> + */
> +
> +#include <linux/vfio.h>
> +#include <sys/ioctl.h>
> +#include "qemu/osdep.h"
> +#include "qapi/error.h"
> +#include "hw/sysbus.h"
> +#include "hw/vfio/vfio.h"
> +#include "hw/vfio/vfio-common.h"
> +#include "hw/s390x/ap-device.h"
> +#include "qemu/error-report.h"
> +#include "qemu/queue.h"
> +#include "qemu/option.h"
> +#include "qemu/config-file.h"
> +#include "cpu.h"
> +#include "kvm_s390x.h"
> +#include "sysemu/sysemu.h"
> +
> +#define VFIO_AP_DEVICE_TYPE      "vfio-ap"
> +
> +typedef struct VFIOAPDevice {
> +    APDevice apdev;
> +    VFIODevice vdev;
> +    QTAILQ_ENTRY(VFIOAPDevice) sibling;
> +} VFIOAPDevice;
> +
> +VFIOAPDevice *vfio_apdev;
> +
> +static void vfio_ap_compute_needs_reset(VFIODevice *vdev)
> +{
> +    vdev->needs_reset = false;
> +}
> +
> +/*
> + * We don't need vfio_hot_reset_multi and vfio_eoi operations for
> + * vfio-ap-matrix device now.
> + */
> +struct VFIODeviceOps vfio_ap_ops = {
> +    .vfio_compute_needs_reset = vfio_ap_compute_needs_reset,
> +};
> +

I'm not familiar with the vfio infrastructure, but AFAIR I
haven't seen any substantial reset handling (QEMU or kernel).
Did I miss something?

If I did not. I think this is a big problem. We need to at least
zeroize the queues (e.g. on system reset)  to avoid leaking
sensitive information. Without this, there is no sane way to use
ap-passthrough. Or am I wrong?

Regards,
Halil