Re: [RFC PATCH v1 5/8] vfio-ccw: Add support for the schib region

[Cornelia Huck <cohuck@redhat.com>]

On Fri, 15 Nov 2019 04:34:34 +0100
Eric Farman <farman@linux.ibm.com> wrote:

> From: Farhan Ali <alifm@linux.ibm.com>
> 
> The schib region can be used to obtain the latest SCHIB from the host
> passthrough subchannel. Since the guest SCHIB is virtualized,
> we currently only update the path related information so that the
> guest is aware of any path related changes when it issues the
> 'stsch' instruction.

One important information here is that you tweak the generic stsch
handling, although the behaviour remains the same for non-vfio
subchannels.

> 
> Signed-off-by: Farhan Ali <alifm@linux.ibm.com>
> Signed-off-by: Eric Farman <farman@linux.ibm.com>
> ---
> 
> Notes:
>     v0->v1: [EF]
>      - Change various incarnations of "update chp status" to
>        "handle_store", to reflect the STSCH instruction that will
>        drive this code
>      - Remove temporary variable for casting/testing purposes in
>        s390_ccw_store(), and add a block comment of WHY its there.
>      - Add a few comments to vfio_ccw_handle_store()
> 
>  hw/s390x/css.c              |  8 ++++--
>  hw/s390x/s390-ccw.c         | 20 +++++++++++++
>  hw/vfio/ccw.c               | 57 +++++++++++++++++++++++++++++++++++++
>  include/hw/s390x/css.h      |  3 +-
>  include/hw/s390x/s390-ccw.h |  1 +
>  target/s390x/ioinst.c       |  3 +-
>  6 files changed, 87 insertions(+), 5 deletions(-)
> 
> diff --git a/hw/s390x/css.c b/hw/s390x/css.c
> index 844caab408..6ee6a96d75 100644
> --- a/hw/s390x/css.c
> +++ b/hw/s390x/css.c
> @@ -1335,11 +1335,15 @@ static void copy_schib_to_guest(SCHIB *dest, const SCHIB *src)
>      }
>  }
>  
> -int css_do_stsch(SubchDev *sch, SCHIB *schib)
> +IOInstEnding css_do_stsch(SubchDev *sch, SCHIB *schib)
>  {
> +    int ret = IOINST_CC_EXPECTED;

It's a bit useless initializing ret here, given that you use it right
below :)

> +

Maybe add a comment here:

       /*
        * For some subchannels, we may want to update parts of
        * the schib (e.g. update path masks from the host device
        * for passthrough subchannels).
        */

> +    ret = s390_ccw_store(sch);
> +
>      /* Use current status. */
>      copy_schib_to_guest(schib, &sch->curr_status);
> -    return 0;
> +    return ret;
>  }
>  
>  static void copy_pmcw_from_guest(PMCW *dest, const PMCW *src)
> diff --git a/hw/s390x/s390-ccw.c b/hw/s390x/s390-ccw.c
> index 0c5a5b60bd..be0b379338 100644
> --- a/hw/s390x/s390-ccw.c
> +++ b/hw/s390x/s390-ccw.c
> @@ -51,6 +51,26 @@ int s390_ccw_clear(SubchDev *sch)
>      return cdc->handle_clear(sch);
>  }
>  
> +IOInstEnding s390_ccw_store(SubchDev *sch)
> +{
> +    S390CCWDeviceClass *cdc = NULL;
> +    int ret = IOINST_CC_EXPECTED;
> +
> +    /*
> +     * This only applies to passthrough devices, so we can't unconditionally
> +     * set this variable like we would for halt/clear.

Hm, can we maybe handle this differently? We have a generic ccw_cb in
the subchannel structure for ccw interpretation; would it make sense to
add a generic callback for stsch there as well?

(This works fine, though. Might want to add the check for halt/clear as
well, but that might be a bit overkill.)

> +     */
> +    if (object_dynamic_cast(OBJECT(sch->driver_data), TYPE_S390_CCW)) {
> +        cdc = S390_CCW_DEVICE_GET_CLASS(sch->driver_data);
> +    }
> +
> +    if (cdc && cdc->handle_store) {
> +        ret = cdc->handle_store(sch);
> +    }
> +
> +    return ret;
> +}
> +
>  static void s390_ccw_get_dev_info(S390CCWDevice *cdev,
>                                    char *sysfsdev,
>                                    Error **errp)
> diff --git a/hw/vfio/ccw.c b/hw/vfio/ccw.c
> index 3e32bc1819..2ff223470f 100644
> --- a/hw/vfio/ccw.c
> +++ b/hw/vfio/ccw.c
> @@ -41,6 +41,9 @@ struct VFIOCCWDevice {
>      uint64_t async_cmd_region_size;
>      uint64_t async_cmd_region_offset;
>      struct ccw_cmd_region *async_cmd_region;
> +    uint64_t schib_region_size;
> +    uint64_t schib_region_offset;
> +    struct ccw_schib_region *schib_region;
>      EventNotifier io_notifier;
>      bool force_orb_pfch;
>      bool warned_orb_pfch;
> @@ -124,6 +127,45 @@ again:
>      }
>  }
>  
> +static IOInstEnding vfio_ccw_handle_store(SubchDev *sch)
> +{
> +    S390CCWDevice *cdev = sch->driver_data;
> +    VFIOCCWDevice *vcdev = DO_UPCAST(VFIOCCWDevice, cdev, cdev);
> +    SCHIB *schib = &sch->curr_status;
> +    struct ccw_schib_region *region = vcdev->schib_region;
> +    SCHIB *s = (SCHIB *)region->schib_area;

You probably don't want to access region until after you checked it's
not NULL :)

> +    int ret;
> +
> +    /* schib region not available so nothing else to do */
> +    if (!region) {
> +        return IOINST_CC_EXPECTED;
> +    }
> +
> +    memset(region, 0, sizeof(*region));
> +    ret = pread(vcdev->vdev.fd, region, vcdev->schib_region_size,
> +                vcdev->schib_region_offset);
> +
> +    if (ret == -1) {
> +        /* Assume device is damaged, regardless of errno */
> +        return IOINST_CC_NOT_OPERATIONAL;

Not sure that's correct; cc 3 for stsch indicates that there are no
more subchannels with higher ids?

> +    }
> +
> +    /*
> +     * Selectively copy path-related bits of the SCHIB,
> +     * rather than copying the entire struct.
> +     */
> +    schib->pmcw.pnom = s->pmcw.pnom;
> +    schib->pmcw.lpum = s->pmcw.lpum;
> +    schib->pmcw.pam = s->pmcw.pam;
> +    schib->pmcw.pom = s->pmcw.pom;
> +
> +    if (s->scsw.flags & SCSW_FLAGS_MASK_PNO) {
> +        schib->scsw.flags |= SCSW_FLAGS_MASK_PNO;
> +    }
> +
> +    return IOINST_CC_EXPECTED;
> +}
> +

The rest of the patch looks good to me.