Date:   Fri, 11 May 2018 11:53:52 +0200
From:   Pierre Morel <pmorel@...ux.ibm.com>
To:     Cornelia Huck <cohuck@...hat.com>,
        Dong Jia Shi <bjsdjshi@...ux.ibm.com>,
        Halil Pasic <pasic@...ux.ibm.com>
Cc:     linux-s390@...r.kernel.org, kvm@...r.kernel.org,
        linux-kernel@...r.kernel.org, qemu-s390x@...gnu.org,
        qemu-devel@...gnu.org
Subject: Re: [PATCH RFC 1/2] vfio-ccw: forward halt/clear to device if
 supported

On 09/05/2018 17:49, Cornelia Huck wrote:
> The initial version of vfio-ccw did not support forwarding of the
> halt or clear functions to the device, and we had to emulate them
> instead.
>
> For versions of the vfio-ccw kernel implementation that indeed do
> support halt/clear (by indicating them in the fctl of the scsw in
> the io_region), we can simply start making use of it. If the kernel
> does not support handling halt/clear, fall back to emulation.
>
> Signed-off-by: Cornelia Huck <cohuck@...hat.com>
> ---
>   hw/s390x/css.c         | 32 ++++++++++++++++++++++++++++----
>   hw/vfio/ccw.c          | 11 +++++++++--
>   include/hw/s390x/css.h | 10 +++++++---
>   3 files changed, 44 insertions(+), 9 deletions(-)
>
> diff --git a/hw/s390x/css.c b/hw/s390x/css.c
> index 301bf1772f..b6727d0607 100644
> --- a/hw/s390x/css.c
> +++ b/hw/s390x/css.c
> @@ -1180,6 +1180,16 @@ static void sch_handle_start_func_virtual(SubchDev *sch)
>   
>   }
>   
> +static IOInstEnding sch_handle_clear_func_passthrough(SubchDev *sch)
> +{
> +    return s390_ccw_cmd_request(sch);
> +}
> +
> +static IOInstEnding sch_handle_halt_func_passthrough(SubchDev *sch)
> +{
> +    return s390_ccw_cmd_request(sch);
> +}
> +
>   static IOInstEnding sch_handle_start_func_passthrough(SubchDev *sch)
>   {
>   
> @@ -1233,13 +1243,27 @@ IOInstEnding do_subchannel_work_virtual(SubchDev *sch)
>   IOInstEnding do_subchannel_work_passthrough(SubchDev *sch)
>   {
>       SCSW *s = &sch->curr_status.scsw;
> +    static bool no_halt_clear;
>   
> +    /* if the kernel does not support halt/clear, fall back to emulation */
>       if (s->ctrl & SCSW_FCTL_CLEAR_FUNC) {
> -        /* TODO: Clear handling */
> -        sch_handle_clear_func(sch);
> +        if (no_halt_clear) {
> +            sch_handle_clear_func(sch);
> +        } else {
> +            if (sch_handle_clear_func_passthrough(sch) == IOINST_OPNOTSUPP) {
> +                no_halt_clear = true;
> +                sch_handle_halt_func(sch);
> +            }
> +        }
>       } else if (s->ctrl & SCSW_FCTL_HALT_FUNC) {
> -        /* TODO: Halt handling */
> -        sch_handle_halt_func(sch);
> +        if (no_halt_clear) {
> +            sch_handle_halt_func(sch);
> +        } else {
> +            if (sch_handle_halt_func_passthrough(sch) == IOINST_OPNOTSUPP) {
> +                no_halt_clear = true;
> +                sch_handle_halt_func(sch);
> +            }
> +        }
>       } else if (s->ctrl & SCSW_FCTL_START_FUNC) {
>           return sch_handle_start_func_passthrough(sch);
>       }
> diff --git a/hw/vfio/ccw.c b/hw/vfio/ccw.c
> index e67392c5f9..247901ae41 100644
> --- a/hw/vfio/ccw.c
> +++ b/hw/vfio/ccw.c
> @@ -60,6 +60,7 @@ static IOInstEnding vfio_ccw_handle_request(SubchDev *sch)
>   
>       memset(region, 0, sizeof(*region));
>   
> +    /* orb is only valid for ssch, but does not hurt for other functions */
>       memcpy(region->orb_area, &sch->orb, sizeof(ORB));
>       memcpy(region->scsw_area, &sch->curr_status.scsw, sizeof(SCSW));
>   
> @@ -70,8 +71,12 @@ again:
>           if (errno == EAGAIN) {
>               goto again;
>           }
> -        error_report("vfio-ccw: wirte I/O region failed with errno=%d", errno);
> -        ret = -errno;
> +        /* handle not supported operations like halt/clear on older kernels */
> +        if (ret != -EOPNOTSUPP) {
> +            error_report("vfio-ccw: write I/O region failed with errno=%d",
> +                         errno);
> +            ret = -errno;
> +        }
>       } else {
>           ret = region->ret_code;
>       }
> @@ -83,6 +88,8 @@ again:
>       case -ENODEV:
>       case -EACCES:
>           return IOINST_CC_NOT_OPERATIONAL;
> +    case -EOPNOTSUPP:
> +        return IOINST_OPNOTSUPP;
>       case -EFAULT:
>       default:
>           sch_gen_unit_exception(sch);
> diff --git a/include/hw/s390x/css.h b/include/hw/s390x/css.h
> index 35facb47d2..e33f26882b 100644
> --- a/include/hw/s390x/css.h
> +++ b/include/hw/s390x/css.h
> @@ -100,9 +100,11 @@ typedef struct CcwDataStream {
>   } CcwDataStream;
>   
>   /*
> - * IO instructions conclude according to this. Currently we have only
> - * cc codes. Valid values are 0, 1, 2, 3 and the generic semantic for
> + * IO instructions conclude according to this. One class of values are
> + * cc codes: Valid values are 0, 1, 2, 3 and the generic semantic for
>    * IO instructions is described briefly. For more details consult the PoP.
> + * Additionally, other endings may occur due to internal processing errors
> + * like lack of support for an operation.
>    */
>   typedef enum IOInstEnding {
>       /* produced expected result */
> @@ -112,7 +114,9 @@ typedef enum IOInstEnding {
>       /* inst. ineffective because busy with previously initiated function */
>       IOINST_CC_BUSY = 2,
>       /* inst. ineffective because not operational */
> -    IOINST_CC_NOT_OPERATIONAL = 3
> +    IOINST_CC_NOT_OPERATIONAL = 3,
> +    /* internal: operation not supported */
> +    IOINST_OPNOTSUPP = 4
>   } IOInstEnding;
>   
>   typedef struct SubchDev SubchDev;


Couldn't we introduce ABI versioning ?


-- 
Pierre Morel
Linux/KVM/QEMU in Böblingen - Germany

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