Commit 9a51c9ee authored by Halil Pasic's avatar Halil Pasic Committed by Cornelia Huck
Browse files

vfio-ccw: add force unlimited prefetch property 



There is at least one guest (OS) such that although it does not rely on
the guarantees provided by ORB 1 word 9 bit (aka unlimited prefetch, aka
P bit) not being set, it fails to tell this to the machine.

Usually this ain't a big deal, as the original purpose of the P bit is to
allow for performance optimizations. vfio-ccw however can not provide the
guarantees required if the bit is not set.

It is not possible to implement support for the P bit not set without
transitioning to lower level protocols for vfio-ccw.  So let's give the
user the opportunity to force setting the P bit, if the user knows this
is safe.  For self modifying channel programs forcing the P bit is not
safe.  If the P bit is forced for a self modifying channel program things
are expected to break in strange ways.

Let's also avoid warning multiple about P bit not set in the ORB in case
P bit is not told to be forced, and designate the affected vfio-ccw
device.

Signed-off-by: default avatarHalil Pasic <pasic@linux.ibm.com>
Suggested-by: default avatarDong Jia Shi <bjsdjshi@linux.ibm.com>
Acked-by: default avatarJason J. Herne <jjherne@linux.ibm.com>
Tested-by: default avatarJason J. Herne <jjherne@linux.ibm.com>
Message-Id: <20180524175828.3143-2-pasic@linux.ibm.com>
Signed-off-by: default avatarCornelia Huck <cohuck@redhat.com>
parent 7a5342e7

hw/s390x/css.c

+1 −2
Original line number Diff line number Diff line
@@ -1204,8 +1204,7 @@ static IOInstEnding sch_handle_start_func_passthrough(SubchDev *sch) 
     * Only support prefetch enable mode.

     * Only support 64bit addressing idal.

     */

    if (!(orb->ctrl0 & ORB_CTRL0_MASK_PFCH) ||

        !(orb->ctrl0 & ORB_CTRL0_MASK_C64)) {

    if (!(orb->ctrl0 & ORB_CTRL0_MASK_C64)) {

        warn_report("vfio-ccw requires PFCH and C64 flags set");

        sch_gen_unit_exception(sch);

        css_inject_io_interrupt(sch);

hw/vfio/ccw.c

+35 −0
Original line number Diff line number Diff line
@@ -33,8 +33,30 @@ typedef struct VFIOCCWDevice { 
    uint64_t io_region_offset;

    struct ccw_io_region *io_region;

    EventNotifier io_notifier;

    bool force_orb_pfch;

    bool warned_orb_pfch;

} VFIOCCWDevice;



static inline void warn_once(bool *warned, const char *fmt, ...)

{

    va_list ap;



    if (!warned || *warned) {

        return;

    }

    *warned = true;

    va_start(ap, fmt);

    warn_vreport(fmt, ap);

    va_end(ap);

}



static inline void warn_once_pfch(VFIOCCWDevice *vcdev, SubchDev *sch,

                                  const char *msg)

{

    warn_once(&vcdev->warned_orb_pfch, "vfio-ccw (devno %x.%x.%04x): %s",

              sch->cssid, sch->ssid, sch->devno, msg);

}



static void vfio_ccw_compute_needs_reset(VFIODevice *vdev)

{

    vdev->needs_reset = false;
@@ -55,6 +77,18 @@ static IOInstEnding vfio_ccw_handle_request(SubchDev *sch) 
    struct ccw_io_region *region = vcdev->io_region;

    int ret;



    if (!(sch->orb.ctrl0 & ORB_CTRL0_MASK_PFCH)) {

        if (!(vcdev->force_orb_pfch)) {

            warn_once_pfch(vcdev, sch, "requires PFCH flag set");

            sch_gen_unit_exception(sch);

            css_inject_io_interrupt(sch);

            return IOINST_CC_EXPECTED;

        } else {

            sch->orb.ctrl0 |= ORB_CTRL0_MASK_PFCH;

            warn_once_pfch(vcdev, sch, "PFCH flag forced");

        }

    }



    QEMU_BUILD_BUG_ON(sizeof(region->orb_area) != sizeof(ORB));

    QEMU_BUILD_BUG_ON(sizeof(region->scsw_area) != sizeof(SCSW));

    QEMU_BUILD_BUG_ON(sizeof(region->irb_area) != sizeof(IRB));
@@ -430,6 +464,7 @@ static void vfio_ccw_unrealize(DeviceState *dev, Error **errp) 


static Property vfio_ccw_properties[] = {

    DEFINE_PROP_STRING("sysfsdev", VFIOCCWDevice, vdev.sysfsdev),

    DEFINE_PROP_BOOL("force-orb-pfch", VFIOCCWDevice, force_orb_pfch, false),

    DEFINE_PROP_END_OF_LIST(),

};