Re: [Qemu-devel] [PATCH v4] s390: diagnose 318 info reset and migration support

[David Hildenbrand <david@redhat.com>]

On 02.05.19 00:31, Collin Walling wrote:
> DIAGNOSE 0x318 (diag318) is a privileged s390x instruction that must
> be intercepted by SIE and handled via KVM. Let's introduce some
> functions to communicate between QEMU and KVM via ioctls. These
> will be used to get/set the diag318 related information (also known
> as the "Control Program Code" or "CPC"), as well as check the system
> if KVM supports handling this instruction.
> 
> The availability of this instruction is determined by byte 134, bit 0
> of the Read Info block. This coincidentally expands into the space used
> for CPU entries, which means VMs running with the diag318 capability
> will have a reduced maximum CPU count. To alleviate this, let's calculate
> the actual max CPU entry space by subtracting the size of Read Info from
> the SCCB size then dividing that number by the size of a CPU entry. If
> this value is less than the value denoted by S390_MAX_CPUS, then let's
> reduce the max cpus for s390 from 248 to 240 in an effort to anticipate
> this potentially happening again in the future.
> 
> In order to simplify the migration and system reset requirements of
> the diag318 data, let's introduce it as a device class and include
> a VMStateDescription.
> 
> Diag318 is reset on during modified clear and load normal.
> 
> Signed-off-by: Collin Walling <walling@linux.ibm.com>
> ---
>  hw/s390x/Makefile.objs       |   1 +
>  hw/s390x/diag318.c           | 100 +++++++++++++++++++++++++++++++++++++++++++
>  hw/s390x/diag318.h           |  39 +++++++++++++++++
>  hw/s390x/s390-virtio-ccw.c   |  23 ++++++++++
>  hw/s390x/sclp.c              |   5 +++
>  include/hw/s390x/sclp.h      |   2 +
>  linux-headers/asm-s390/kvm.h |   4 ++
>  target/s390x/kvm-stub.c      |  15 +++++++
>  target/s390x/kvm.c           |  32 ++++++++++++++
>  target/s390x/kvm_s390x.h     |   3 ++
>  10 files changed, 224 insertions(+)
>  create mode 100644 hw/s390x/diag318.c
>  create mode 100644 hw/s390x/diag318.h
> 
> diff --git a/hw/s390x/Makefile.objs b/hw/s390x/Makefile.objs
> index e02ed80..93621dc 100644
> --- a/hw/s390x/Makefile.objs
> +++ b/hw/s390x/Makefile.objs
> @@ -34,3 +34,4 @@ obj-$(CONFIG_KVM) += s390-stattrib-kvm.o
>  obj-y += s390-ccw.o
>  obj-y += ap-device.o
>  obj-y += ap-bridge.o
> +obj-y += diag318.o
> diff --git a/hw/s390x/diag318.c b/hw/s390x/diag318.c
> new file mode 100644
> index 0000000..94b44da
> --- /dev/null
> +++ b/hw/s390x/diag318.c
> @@ -0,0 +1,100 @@
> +/*
> + * DIAGNOSE 0x318 functions for reset and migration
> + *
> + * Copyright IBM, Corp. 2019
> + *
> + * Authors:
> + *  Collin Walling <walling@linux.ibm.com>
> + *
> + * This work is licensed under the terms of the GNU GPL, version 2 or (at your
> + * option) any later version. See the COPYING file in the top-level directory.
> + */
> +
> +#include "hw/s390x/diag318.h"
> +#include "qapi/error.h"
> +#include "kvm_s390x.h"
> +#include "sysemu/kvm.h"
> +
> +static int diag318_post_load(void *opaque, int version_id)
> +{
> +    DIAG318State *d = opaque;
> +
> +    kvm_s390_set_cpc(d->cpc);
> +
> +    /* It is not necessary to retain a copy of the cpc after migration. */
> +    d->cpc = 0;
> +
> +    return 0;
> +}
> +
> +static int diag318_pre_save(void *opaque)
> +{
> +    DIAG318State *d = opaque;
> +
> +    kvm_s390_get_cpc(&d->cpc);
> +    return 0;
> +}
> +
> +static bool diag318_needed(void *opaque)
> +{
> +    DIAG318State *d = opaque;
> +
> +    return d->enabled;
> +}
> +
> +const VMStateDescription vmstate_diag318 = {
> +    .name = "vmstate_diag318",
> +    .post_load = diag318_post_load,
> +    .pre_save = diag318_pre_save,
> +    .version_id = 1,
> +    .minimum_version_id = 1,
> +    .needed = diag318_needed,
> +    .fields = (VMStateField[]) {
> +        VMSTATE_UINT64(cpc, DIAG318State),
> +        VMSTATE_END_OF_LIST()
> +    }
> +};
> +
> +static void s390_diag318_realize(DeviceState *dev, Error **errp)
> +{
> +    DIAG318State *d = DIAG318(dev);
> +
> +    if (kvm_s390_has_diag318()) {
> +        d->enabled = true;
> +    }
> +}
> +
> +static void s390_diag318_reset(DeviceState *dev)
> +{
> +    DIAG318State *d = DIAG318(dev);
> +
> +    if (d->enabled) {
> +        kvm_s390_set_cpc(0);
> +    }
> +}
> +
> +static void s390_diag318_class_init(ObjectClass *klass, void *data)
> +{
> +    DeviceClass *dc = DEVICE_CLASS(klass);
> +
> +    dc->realize = s390_diag318_realize;
> +    dc->reset = s390_diag318_reset;
> +    dc->vmsd = &vmstate_diag318;
> +    dc->hotpluggable = false;
> +    /* Reason: Set automatically during IPL */
> +    dc->user_creatable = false;
> +}
> +
> +static const TypeInfo s390_diag318_info = {
> +    .class_init = s390_diag318_class_init,
> +    .parent = TYPE_DEVICE,
> +    .name = TYPE_S390_DIAG318,
> +    .instance_size = sizeof(DIAG318State),
> +};
> +
> +static void s390_diag318_register_types(void)
> +{
> +    type_register_static(&s390_diag318_info);
> +}
> +
> +type_init(s390_diag318_register_types)
> diff --git a/hw/s390x/diag318.h b/hw/s390x/diag318.h
> new file mode 100644
> index 0000000..c154b0a
> --- /dev/null
> +++ b/hw/s390x/diag318.h
> @@ -0,0 +1,39 @@
> +/*
> + * DIAGNOSE 0x318 functions for reset and migration
> + *
> + * Copyright IBM, Corp. 2019
> + *
> + * Authors:
> + *  Collin Walling <walling@linux.ibm.com>
> + *
> + * This work is licensed under the terms of the GNU GPL, version 2 or (at your
> + * option) any later version. See the COPYING file in the top-level directory.
> + */
> +
> + #ifndef DIAG318_H
> + #define DIAG318_H
> +
> +#include "qemu/osdep.h"
> +#include "hw/qdev.h"
> +
> +#define TYPE_S390_DIAG318 "diag318"
> +#define DIAG318(obj) \
> +    OBJECT_CHECK(DIAG318State, (obj), TYPE_S390_DIAG318)
> +
> +typedef struct DIAG318State {
> +    /*< private >*/
> +    DeviceState parent_obj;
> +
> +    /*< public >*/
> +    uint64_t cpc;
> +    bool enabled;
> +} DIAG318State;
> +
> +typedef struct DIAG318Class {
> +    /*< private >*/
> +    DeviceClass parent_class;
> +
> +    /*< public >*/
> +} DIAG318Class;
> +
> +#endif /* DIAG318_H */
> diff --git a/hw/s390x/s390-virtio-ccw.c b/hw/s390x/s390-virtio-ccw.c
> index d11069b..44a424b 100644
> --- a/hw/s390x/s390-virtio-ccw.c
> +++ b/hw/s390x/s390-virtio-ccw.c
> @@ -36,6 +36,7 @@
>  #include "cpu_models.h"
>  #include "hw/nmi.h"
>  #include "hw/s390x/tod.h"
> +#include "hw/s390x/diag318.h"
>  
>  S390CPU *s390_cpu_addr2state(uint16_t cpu_addr)
>  {
> @@ -92,6 +93,7 @@ static const char *const reset_dev_types[] = {
>      "s390-sclp-event-facility",
>      "s390-flic",
>      "diag288",
> +    TYPE_S390_DIAG318,
>  };
>  
>  static void subsystem_reset(void)
> @@ -246,6 +248,17 @@ static void s390_create_sclpconsole(const char *type, Chardev *chardev)
>      qdev_init_nofail(dev);
>  }
>  
> +static void s390_init_diag318(void)
> +{
> +    Object *new = object_new(TYPE_S390_DIAG318);
> +    DeviceState *dev = DEVICE(new);
> +
> +    object_property_add_child(qdev_get_machine(), TYPE_S390_DIAG318,
> +                              new, NULL);
> +    object_unref(new);
> +    qdev_init_nofail(dev);
> +}
> +
>  static void ccw_init(MachineState *machine)
>  {
>      int ret;
> @@ -302,6 +315,8 @@ static void ccw_init(MachineState *machine)
>  
>      /* init the TOD clock */
>      s390_init_tod();
> +
> +    s390_init_diag318();
>  }
>  
>  static void s390_cpu_plug(HotplugHandler *hotplug_dev,
> @@ -570,6 +585,7 @@ static void machine_set_loadparm(Object *obj, const char *val, Error **errp)
>          ms->loadparm[i] = ' '; /* pad right with spaces */
>      }
>  }
> +
>  static inline void s390_machine_initfn(Object *obj)
>  {
>      object_property_add_bool(obj, "aes-key-wrap",
> @@ -652,6 +668,13 @@ static void ccw_machine_4_0_instance_options(MachineState *machine)
>  
>  static void ccw_machine_4_0_class_options(MachineClass *mc)
>  {
> +    /*
> +     * Read Info might reveal more bytes used to detect facilities, thus
> +     * reducing the number of CPU entries. Let's reduce the max CPUs by
> +     * an arbitrary number in effort to anticipate future facility bytes.
> +     */
> +    if ((SCCB_SIZE - sizeof(ReadInfo)) / sizeof(CPUEntry) < S390_MAX_CPUS)
> +        mc->max_cpus = S390_MAX_CPUS - 8;

This is too complicated, just set it always to 240.

However, I am still not sure how to best handle this scenario. One
solution is

1. Set it statically to 240 for machine > 4.1
2. Keep the old machines unmodifed
3. Don't indicate the CPU feature for machines <= 4.0

#3 is the problematic part, as it mixes host CPU features and machines.
Bad. The host CPU model should always look the same on all machines. I
don't like this.

-- 

Thanks,

David / dhildenb