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

[Tony Krowiak <akrowiak@linux.vnet.ibm.com>]

On 05/09/2018 10:28 AM, Halil Pasic wrote:
>
>
> 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?

No, you didn't miss anything, there is no reset handling.

>
> 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?

I do not have a definitive answer, I will have to look into it.
I'm thinking that since we are using ap-passthrough, the AP bus
running on the guest would be responsible for handling reset possibly
by resetting or zeroizing its queues. I'll get back to you on this.

>
> Regards,
> Halil
>