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

[David Hildenbrand <david@redhat.com>]

On 09.05.19 11:58, Christian Borntraeger wrote:
> 
> 
> 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;
> 
> But we also do not need to zero it out? Can't you just drop these 2 lines?
> 
> 
>> +
>> +    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;
>> +}
> 
> I would like to have a cpumodel entry that allows to disable that feature. And we should
> then check for this.
> 
>> +
>> +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;
>> +    }
> 
> same here -> cpumodel
> Then we can get rid of the enabled bool.
>> +}
>> +
>> +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;
> 
> Maybe this should depend on the presence of this feature in the cpumodel?
> 
>>  }
>>  DEFINE_CCW_MACHINE(4_0, "4.0", true);
>>  
>> diff --git a/hw/s390x/sclp.c b/hw/s390x/sclp.c
>> index 4510a80..9cfa188 100644
>> --- a/hw/s390x/sclp.c
>> +++ b/hw/s390x/sclp.c
>> @@ -22,6 +22,7 @@
>>  #include "hw/s390x/event-facility.h"
>>  #include "hw/s390x/s390-pci-bus.h"
>>  #include "hw/s390x/ipl.h"
>> +#include "kvm_s390x.h"
>>  
>>  static inline SCLPDevice *get_sclp_device(void)
>>  {
>> @@ -74,6 +75,10 @@ static void read_SCP_info(SCLPDevice *sclp, SCCB *sccb)
>>      s390_get_feat_block(S390_FEAT_TYPE_SCLP_CONF_CHAR_EXT,
>>                           read_info->conf_char_ext);
>>  
>> +    /* Enable diag318 for guest if KVM supports emulation */
>> +    if (kvm_s390_has_diag318())
>> +        read_info->fac134 = 0x80;
> 
> I think we should rather make this part of the cpumodel

+1, had the same idea when skimming over this.


-- 

Thanks,

David / dhildenb