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

[Tony Krowiak]

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