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

[Tony Krowiak]

On 05/16/2018 05:09 AM, Pierre Morel wrote:
> On 15/05/2018 17:09, Tony Krowiak wrote:
> > On 05/15/2018 03:55 AM, Pierre Morel wrote:
> > > On 14/05/2018 21:26, Tony Krowiak wrote:
> > > > On 05/11/2018 05:02 AM, Pierre Morel wrote:
> > > > > On 10/05/2018 15:10, Tony Krowiak wrote:
> > > > > > 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
> > > > > On the host, on system reset or subsystem reset, the queues are 
> > > > > zeroized.
> > > >
> > > > Can you point me to where this is done?
> > >
> > > This is firmware. See documentation, it is specified that the queues 
> > > are zeroized on system or subsystem reset.
> >
> > The sticking point for me is how does this relate to the guest 
> > running under SIE?
>
> No it has nothing to do with the SIE, therefor we must do it explicitly.

It shall be done.

> Regards,
>
> Pierre