Re: [PATCH v6 2/2] s390: diagnose 318 info reset and migration support

[Collin Walling <walling@linux.ibm.com>]

On 1/27/20 6:47 AM, Cornelia Huck wrote:
> On Fri, 24 Jan 2020 17:14:04 -0500
> Collin Walling <walling@linux.ibm.com> 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 information.
> 
> Do you want to give a hint what diag 318 actually does?
> 

For the sake of completeness, I'll have to get back to you on this.

>>
>> The availability of this instruction is determined by byte 134, bit 0
>> of the Read Info block. This coincidentally expands into the space used
> 
> "SCLP Read Info"
> 
>> for CPU entries by taking away one byte, which means VMs running with
>> the diag318 capability will not be able to retrieve information regarding
>> the 248th CPU. This will not effect performance, and VMs can still be
>> ran with 248 CPUs.
> 
> Are there other ways in which that might affect guests? I assume Linux
> can deal with it? Is it ok architecture-wise?
> 
> In any case, should go into the patch description :)
> 

Same as above. I'll try to provide more information regarding what happens
here in my next reply.

>>
>> 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 set to 0 during modified clear and load normal resets.
> 
> What exactly is set to 0? Stored values?
> 

Correct. "The stored values set by DIAG318 are reset to 0 during..."

>>
>> Signed-off-by: Collin Walling <walling@linux.ibm.com>
>> ---
>>  hw/s390x/Makefile.objs              |  1 +
>>  hw/s390x/diag318.c                  | 85 +++++++++++++++++++++++++++++++++++++
>>  hw/s390x/diag318.h                  | 40 +++++++++++++++++
>>  hw/s390x/s390-virtio-ccw.c          | 17 ++++++++
>>  hw/s390x/sclp.c                     | 13 ++++++
>>  include/hw/s390x/sclp.h             |  2 +
>>  target/s390x/cpu_features.h         |  1 +
>>  target/s390x/cpu_features_def.inc.h |  3 ++
>>  target/s390x/gen-features.c         |  1 +
>>  target/s390x/kvm-stub.c             | 10 +++++
>>  target/s390x/kvm.c                  | 29 +++++++++++++
>>  target/s390x/kvm_s390x.h            |  2 +
>>  12 files changed, 204 insertions(+)
>>  create mode 100644 hw/s390x/diag318.c
>>  create mode 100644 hw/s390x/diag318.h
>>
> (...)
>> diff --git a/hw/s390x/diag318.c b/hw/s390x/diag318.c
>> new file mode 100644
>> index 0000000..2d30bb2
>> --- /dev/null
>> +++ b/hw/s390x/diag318.c
>> @@ -0,0 +1,85 @@
>> +/*
>> + * DIAGNOSE 0x318 functions for reset and migration
>> + *
>> + * Copyright IBM, Corp. 2019
> 
> Happy new year?
> 

Woo!

>> + *
>> + * 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;
>> +
>> +    if (kvm_enabled())
> 
> As already noted by patchew, this needs some curly braces.
> 
>> +        kvm_s390_set_diag318_info(d->info);
>> +
>> +    return 0;
>> +}
>> +
>> +static int diag318_pre_save(void *opaque)
>> +{
>> +    DIAG318State *d = opaque;
>> +
>> +    if (kvm_enabled())
> 
> braces
> 
>> +        kvm_s390_get_diag318_info(&d->info);
>> +
>> +    return 0;
>> +}
>> +
>> +static bool diag318_needed(void *opaque)
>> +{
>> +    return kvm_enabled() ? s390_has_feat(S390_FEAT_DIAG318) : 0;
> 
> Why do you need to guard this with kvm_enabled()? If tcg does not
> enable the feature, we should be fine; and if it emulates this in the
> future, we probably need to migrate something anyway.
> 

Your explanation makes sense. My thoughts were to not even bother
registering the state description if KVM isn't enabled (but I guess
that thinking would mean that the other kvm_enabled fencing would
be redundant? Doh.)

I'll fix 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(info, DIAG318State),
>> +        VMSTATE_END_OF_LIST()
>> +    }
>> +};
>> +
>> +static void s390_diag318_reset(DeviceState *dev)
>> +{
>> +    if (kvm_enabled())
> 
> braces
> 
>> +        kvm_s390_set_diag318_info(0);
>> +}
>> +
>> +static void s390_diag318_class_init(ObjectClass *klass, void *data)
>> +{
>> +    DeviceClass *dc = DEVICE_CLASS(klass);
>> +
>> +    dc->reset = s390_diag318_reset;
>> +    dc->vmsd = &vmstate_diag318;
>> +    dc->hotpluggable = false;
>> +    /* Reason: Created automatically during machine instantiation */
>> +    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..06d9f67
>> --- /dev/null
>> +++ b/hw/s390x/diag318.h
>> @@ -0,0 +1,40 @@
>> +/*
>> + * DIAGNOSE 0x318 functions for reset and migration
>> + *
>> + * Copyright IBM, Corp. 2019
> 
> Again, the year needs an update.
> 
>> + *
>> + * 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 HW_DIAG318_H
>> +#define HW_DIAG318_H
>> +
>> +#include "qemu/osdep.h"
>> +#include "migration/vmstate.h"
>> +#include "qom/object.h"
>> +#include "hw/qdev-core.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 info;
>> +} DIAG318State;
>> +
>> +typedef struct DIAG318Class {
>> +    /*< private >*/
>> +    DeviceClass parent_class;
>> +
>> +    /*< public >*/
>> +} DIAG318Class;
>> +
>> +#endif /* HW_DIAG318_H */
>> \ No newline at end of file
> 
> And please add a newline :)
> 
>> diff --git a/hw/s390x/s390-virtio-ccw.c b/hw/s390x/s390-virtio-ccw.c
>> index e0e2813..d5b7a33 100644
>> --- a/hw/s390x/s390-virtio-ccw.c
>> +++ b/hw/s390x/s390-virtio-ccw.c
>> @@ -41,6 +41,7 @@
>>  #include "hw/qdev-properties.h"
>>  #include "hw/s390x/tod.h"
>>  #include "sysemu/sysemu.h"
>> +#include "hw/s390x/diag318.h"
>>  
>>  S390CPU *s390_cpu_addr2state(uint16_t cpu_addr)
>>  {
>> @@ -97,6 +98,7 @@ static const char *const reset_dev_types[] = {
>>      "s390-sclp-event-facility",
>>      "s390-flic",
>>      "diag288",
>> +    TYPE_S390_DIAG318,
>>  };
>>  
>>  static void subsystem_reset(void)
>> @@ -237,6 +239,17 @@ 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;
>> @@ -294,6 +307,9 @@ static void ccw_init(MachineState *machine)
>>  
>>      /* init the TOD clock */
>>      s390_init_tod();
>> +
>> +    /* init object used for migrating diag318 info */
>> +    s390_init_diag318();
> 
> Doesn't that device do a bit more than 'migrating' info?
> 
> Also, it seems a bit useless unless you're running with kvm and the
> feature bit switched on...
> 

Right... I think this whole "diag318 device" thing needs some rethinking.

I made a comment on David's response regarding where to but the VMStateDescription
code for diag318. Perhaps including the related information within the S390MachineState
would be better? (I'm not sure).

>>  }
>>  
>>  static void s390_cpu_plug(HotplugHandler *hotplug_dev,
>> @@ -566,6 +582,7 @@ static void machine_set_loadparm(Object *obj, const char *val, Error **errp)
>>          ms->loadparm[i] = ' '; /* pad right with spaces */
>>      }
>>  }
>> +
> 
> Still whitespace :)
> 
>>  static inline void s390_machine_initfn(Object *obj)
>>  {
>>      object_property_add_bool(obj, "aes-key-wrap",
>> diff --git a/hw/s390x/sclp.c b/hw/s390x/sclp.c
>> index f57ce7b..636348c 100644
>> --- a/hw/s390x/sclp.c
>> +++ b/hw/s390x/sclp.c
>> @@ -15,6 +15,7 @@
>>  #include "qemu/osdep.h"
>>  #include "qemu/units.h"
>>  #include "qapi/error.h"
>> +#include "qemu/error-report.h"
>>  #include "cpu.h"
>>  #include "sysemu/sysemu.h"
>>  #include "hw/boards.h"
>> @@ -22,6 +23,7 @@
>>  #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)
>>  {
>> @@ -37,10 +39,19 @@ static void prepare_cpu_entries(SCLPDevice *sclp, CPUEntry *entry, int *count)
>>  {
>>      MachineState *ms = MACHINE(qdev_get_machine());
>>      uint8_t features[SCCB_CPU_FEATURE_LEN] = { 0 };
>> +    int max_entries;
>>      int i;
>>  
>> +    /* Calculate the max number of CPU entries that can be stored in the SCCB */
>> +    max_entries = (SCCB_SIZE - offsetof(ReadInfo, entries)) / sizeof(CPUEntry);
>> +
>>      s390_get_feat_block(S390_FEAT_TYPE_SCLP_CPU, features);
>>      for (i = 0, *count = 0; i < ms->possible_cpus->len; i++) {
>> +        if (*count == max_entries) {
>> +            warn_report("Configuration only supports a max of %d CPU entries.",
>> +                        max_entries);
> 
> IIUC, this only moans during Read Info... but you could previously add
> more cpus than what could be serviced by Read Info. So, it looks to me
> you get some messages when a guest is doing Read Info; that seems more
> confusing than helpful to me. Can't we rather warn at cpu instantiation
> time?
> 

Ahh, I didn't think of that. For some reason, I was thinking that Read Info
would only be queried once.

Yes, this makes sense. I'll relocate the warning message...

>> +            break;
>> +        }
>>          if (!ms->possible_cpus->cpus[i].cpu) {
>>              continue;
>>          }
>> @@ -80,6 +91,8 @@ 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);
>>  
>> +    s390_get_feat_block(S390_FEAT_TYPE_SCLP_BYTE_134, read_info->byte_134);
>> +
>>      read_info->facilities = cpu_to_be64(SCLP_HAS_CPU_INFO |
>>                                          SCLP_HAS_IOA_RECONFIG);
>>  
> 
> (...)
> 
> 

I've noted the nits as well. Thanks for your review!


-- 
Respectfully,
- Collin Walling