Re: [Qemu-devel] [PATCH RFCv2] s390x/sclp: remove memory hotplug support

[Christian Borntraeger]

On 02/19/2018 06:42 PM, David Hildenbrand wrote:
> From an architecture point of view, nothing can be mapped into the address
> space on s390x. All there is is memory. Therefore there is also not really
> an interface to communicate such information to the guest. All we can do is
> specify the maximum ram address and guests can probe in that range if
> memory is available and usable (TPROT).

In fact there is an interface in SCLP that describes the memory sizes (maximum 
in 
read scp info) and the details (read_storage_element0_info).  I am asking myself
if we should re-introduce read_storage_element_info and use that to avoid tprot
in the guests. Anyway that is future but maybe change your "TPROT" to sclp + 
tprot.


> 
> Also memory hotplug is strange. The guest can decide at some point in
> time to add / remove memory in some range. And nobody can really hinder it
> from doing so.

The host can reject to online an increment. For example on LPAR this is used as
a poor mans overcommitment. You can online prepared standy memory if there is
enough memory left.

 So if we specify right now e.g.
>     -m 2G,slots=2,maxmem=20G
> An ordinary fedora guest will happily online (hotplug) all memory,
> resulting in a guest consuming 20G. So it really behaves rather like
>     -m 22G
> There is no way to hotplug memory from the outside like on other
> architectures. This is of course bad for upper management layers.

This is the main issue with the current code.

> 
> As the guest can create/delete memory regions while it is running, of
> course migration support is not available and tricky to implement.
> 
> With virtualization, it is different. We might want to map something
> into guest address space (e.g. fake DAX devices) and not detect it
> automatically as memory. So we really want to use the maxmem and slots
> parameter just like on all other architectures. Such devices will have
> to expose the applicable memory range themselves. To finally be able to
> provide memory hotplug to guests, we will need a new paravirtualized
> interface to do that (e.g. something into the direction of virtio-mem).
> 
> This implies, that maxmem cannot be used for s390x memory hotplug
> anymore and has to go. This simplifies the code quite a bit.
> 
> As migration support is not working, this change cannot really break
> migration as guests without slots and maxmem don't see the SCLP
> features. Also, the ram size calcualtion does not change.
> 
> Signed-off-by: David Hildenbrand <address@hidden>


code looks sane.

Reviewed-by: Christian Borntraeger <address@hidden>


> ---
>  hw/s390x/sclp.c         | 310 
> +-----------------------------------------------
>  include/hw/s390x/sclp.h |  25 ----
>  target/s390x/cpu.h      |   1 -
>  3 files changed, 5 insertions(+), 331 deletions(-)
> 
> diff --git a/hw/s390x/sclp.c b/hw/s390x/sclp.c
> index 276972b59f..047d577313 100644
> --- a/hw/s390x/sclp.c
> +++ b/hw/s390x/sclp.c
> @@ -15,9 +15,7 @@
>  #include "qemu/osdep.h"
>  #include "qapi/error.h"
>  #include "cpu.h"
> -#include "exec/memory.h"
>  #include "sysemu/sysemu.h"
> -#include "exec/address-spaces.h"
>  #include "hw/boards.h"
>  #include "hw/s390x/sclp.h"
>  #include "hw/s390x/event-facility.h"
> @@ -57,10 +55,8 @@ static void read_SCP_info(SCLPDevice *sclp, SCCB *sccb)
>  {
>      ReadInfo *read_info = (ReadInfo *) sccb;
>      MachineState *machine = MACHINE(qdev_get_machine());
> -    sclpMemoryHotplugDev *mhd = get_sclp_memory_hotplug_dev();
>      int cpu_count;
>      int rnsize, rnmax;
> -    int slots = MIN(machine->ram_slots, s390_get_memslot_count());
>      IplParameterBlock *ipib = s390_ipl_get_iplb();
> 
>      /* CPU information */
> @@ -80,36 +76,6 @@ static void read_SCP_info(SCLPDevice *sclp, SCCB *sccb)
>      read_info->facilities = cpu_to_be64(SCLP_HAS_CPU_INFO |
>                                          SCLP_HAS_IOA_RECONFIG);
> 
> -    /* Memory Hotplug is only supported for the ccw machine type */
> -    if (mhd) {
> -        mhd->standby_subregion_size = MEM_SECTION_SIZE;
> -        /* Deduct the memory slot already used for core */
> -        if (slots > 0) {
> -            while ((mhd->standby_subregion_size * (slots - 1)
> -                    < mhd->standby_mem_size)) {
> -                mhd->standby_subregion_size = mhd->standby_subregion_size << 
> 1;
> -            }
> -        }
> -        /*
> -         * Initialize mapping of guest standby memory sections indicating 
> which
> -         * are and are not online. Assume all standby memory begins offline.
> -         */
> -        if (mhd->standby_state_map == 0) {
> -            if (mhd->standby_mem_size % mhd->standby_subregion_size) {
> -                mhd->standby_state_map = g_malloc0((mhd->standby_mem_size /
> -                                             mhd->standby_subregion_size + 
> 1) *
> -                                             (mhd->standby_subregion_size /
> -                                             MEM_SECTION_SIZE));
> -            } else {
> -                mhd->standby_state_map = g_malloc0(mhd->standby_mem_size /
> -                                                   MEM_SECTION_SIZE);
> -            }
> -        }
> -        mhd->padded_ram_size = ram_size + mhd->pad_size;
> -        mhd->rzm = 1 << mhd->increment_size;
> -
> -        read_info->facilities |= 
> cpu_to_be64(SCLP_FC_ASSIGN_ATTACH_READ_STOR);
> -    }
>      read_info->mha_pow = s390_get_mha_pow();
>      read_info->hmfai = cpu_to_be32(s390_get_hmfai());
> 
> @@ -121,7 +87,8 @@ static void read_SCP_info(SCLPDevice *sclp, SCCB *sccb)
>          read_info->rnsize2 = cpu_to_be32(rnsize);
>      }
> 
> -    rnmax = machine->maxram_size >> sclp->increment_size;
> +    /* we don't support standby memory, maxram_size is never exposed */
> +    rnmax = machine->ram_size >> sclp->increment_size;
>      if (rnmax < 0x10000) {
>          read_info->rnmax = cpu_to_be16(rnmax);
>      } else {
> @@ -139,195 +106,6 @@ static void read_SCP_info(SCLPDevice *sclp, SCCB *sccb)
>      sccb->h.response_code = cpu_to_be16(SCLP_RC_NORMAL_READ_COMPLETION);
>  }
> 
> -static void read_storage_element0_info(SCLPDevice *sclp, SCCB *sccb)
> -{
> -    int i, assigned;
> -    int subincrement_id = SCLP_STARTING_SUBINCREMENT_ID;
> -    ReadStorageElementInfo *storage_info = (ReadStorageElementInfo *) sccb;
> -    sclpMemoryHotplugDev *mhd = get_sclp_memory_hotplug_dev();
> -
> -    if (!mhd) {
> -        sccb->h.response_code = cpu_to_be16(SCLP_RC_INVALID_SCLP_COMMAND);
> -        return;
> -    }
> -
> -    if ((ram_size >> mhd->increment_size) >= 0x10000) {
> -        sccb->h.response_code = cpu_to_be16(SCLP_RC_SCCB_BOUNDARY_VIOLATION);
> -        return;
> -    }
> -
> -    /* Return information regarding core memory */
> -    storage_info->max_id = cpu_to_be16(mhd->standby_mem_size ? 1 : 0);
> -    assigned = ram_size >> mhd->increment_size;
> -    storage_info->assigned = cpu_to_be16(assigned);
> -
> -    for (i = 0; i < assigned; i++) {
> -        storage_info->entries[i] = cpu_to_be32(subincrement_id);
> -        subincrement_id += SCLP_INCREMENT_UNIT;
> -    }
> -    sccb->h.response_code = cpu_to_be16(SCLP_RC_NORMAL_READ_COMPLETION);
> -}
> -
> -static void read_storage_element1_info(SCLPDevice *sclp, SCCB *sccb)
> -{
> -    ReadStorageElementInfo *storage_info = (ReadStorageElementInfo *) sccb;
> -    sclpMemoryHotplugDev *mhd = get_sclp_memory_hotplug_dev();
> -
> -    if (!mhd) {
> -        sccb->h.response_code = cpu_to_be16(SCLP_RC_INVALID_SCLP_COMMAND);
> -        return;
> -    }
> -
> -    if ((mhd->standby_mem_size >> mhd->increment_size) >= 0x10000) {
> -        sccb->h.response_code = cpu_to_be16(SCLP_RC_SCCB_BOUNDARY_VIOLATION);
> -        return;
> -    }
> -
> -    /* Return information regarding standby memory */
> -    storage_info->max_id = cpu_to_be16(mhd->standby_mem_size ? 1 : 0);
> -    storage_info->assigned = cpu_to_be16(mhd->standby_mem_size >>
> -                                         mhd->increment_size);
> -    storage_info->standby = cpu_to_be16(mhd->standby_mem_size >>
> -                                        mhd->increment_size);
> -    sccb->h.response_code = cpu_to_be16(SCLP_RC_STANDBY_READ_COMPLETION);
> -}
> -
> -static void attach_storage_element(SCLPDevice *sclp, SCCB *sccb,
> -                                   uint16_t element)
> -{
> -    int i, assigned, subincrement_id;
> -    AttachStorageElement *attach_info = (AttachStorageElement *) sccb;
> -    sclpMemoryHotplugDev *mhd = get_sclp_memory_hotplug_dev();
> -
> -    if (!mhd) {
> -        sccb->h.response_code = cpu_to_be16(SCLP_RC_INVALID_SCLP_COMMAND);
> -        return;
> -    }
> -
> -    if (element != 1) {
> -        sccb->h.response_code = cpu_to_be16(SCLP_RC_INVALID_SCLP_COMMAND);
> -        return;
> -    }
> -
> -    assigned = mhd->standby_mem_size >> mhd->increment_size;
> -    attach_info->assigned = cpu_to_be16(assigned);
> -    subincrement_id = ((ram_size >> mhd->increment_size) << 16)
> -                      + SCLP_STARTING_SUBINCREMENT_ID;
> -    for (i = 0; i < assigned; i++) {
> -        attach_info->entries[i] = cpu_to_be32(subincrement_id);
> -        subincrement_id += SCLP_INCREMENT_UNIT;
> -    }
> -    sccb->h.response_code = cpu_to_be16(SCLP_RC_NORMAL_COMPLETION);
> -}
> -
> -static void assign_storage(SCLPDevice *sclp, SCCB *sccb)
> -{
> -    MemoryRegion *mr = NULL;
> -    uint64_t this_subregion_size;
> -    AssignStorage *assign_info = (AssignStorage *) sccb;
> -    sclpMemoryHotplugDev *mhd = get_sclp_memory_hotplug_dev();
> -    ram_addr_t assign_addr;
> -    MemoryRegion *sysmem = get_system_memory();
> -
> -    if (!mhd) {
> -        sccb->h.response_code = cpu_to_be16(SCLP_RC_INVALID_SCLP_COMMAND);
> -        return;
> -    }
> -    assign_addr = (be16_to_cpu(assign_info->rn) - 1) * mhd->rzm;
> -
> -    if ((assign_addr % MEM_SECTION_SIZE == 0) &&
> -        (assign_addr >= mhd->padded_ram_size)) {
> -        /* Re-use existing memory region if found */
> -        mr = memory_region_find(sysmem, assign_addr, 1).mr;
> -        memory_region_unref(mr);
> -        if (!mr) {
> -
> -            MemoryRegion *standby_ram = g_new(MemoryRegion, 1);
> -
> -            /* offset to align to standby_subregion_size for allocation */
> -            ram_addr_t offset = assign_addr -
> -                                (assign_addr - mhd->padded_ram_size)
> -                                % mhd->standby_subregion_size;
> -
> -            /* strlen("standby.ram") + 4 (Max of KVM_MEMORY_SLOTS) +  NULL */
> -            char id[16];
> -            snprintf(id, 16, "standby.ram%d",
> -                     (int)((offset - mhd->padded_ram_size) /
> -                     mhd->standby_subregion_size) + 1);
> -
> -            /* Allocate a subregion of the calculated standby_subregion_size 
> */
> -            if (offset + mhd->standby_subregion_size >
> -                mhd->padded_ram_size + mhd->standby_mem_size) {
> -                this_subregion_size = mhd->padded_ram_size +
> -                  mhd->standby_mem_size - offset;
> -            } else {
> -                this_subregion_size = mhd->standby_subregion_size;
> -            }
> -
> -            memory_region_init_ram(standby_ram, NULL, id, 
> this_subregion_size,
> -                                   &error_fatal);
> -            /* This is a hack to make memory hotunplug work again. Once we 
> have
> -             * subdevices, we have to unparent them when unassigning memory,
> -             * instead of doing it via the ref count of the MemoryRegion. */
> -            object_ref(OBJECT(standby_ram));
> -            object_unparent(OBJECT(standby_ram));
> -            memory_region_add_subregion(sysmem, offset, standby_ram);
> -        }
> -        /* The specified subregion is no longer in standby */
> -        mhd->standby_state_map[(assign_addr - mhd->padded_ram_size)
> -                               / MEM_SECTION_SIZE] = 1;
> -    }
> -    sccb->h.response_code = cpu_to_be16(SCLP_RC_NORMAL_COMPLETION);
> -}
> -
> -static void unassign_storage(SCLPDevice *sclp, SCCB *sccb)
> -{
> -    MemoryRegion *mr = NULL;
> -    AssignStorage *assign_info = (AssignStorage *) sccb;
> -    sclpMemoryHotplugDev *mhd = get_sclp_memory_hotplug_dev();
> -    ram_addr_t unassign_addr;
> -    MemoryRegion *sysmem = get_system_memory();
> -
> -    if (!mhd) {
> -        sccb->h.response_code = cpu_to_be16(SCLP_RC_INVALID_SCLP_COMMAND);
> -        return;
> -    }
> -    unassign_addr = (be16_to_cpu(assign_info->rn) - 1) * mhd->rzm;
> -
> -    /* if the addr is a multiple of 256 MB */
> -    if ((unassign_addr % MEM_SECTION_SIZE == 0) &&
> -        (unassign_addr >= mhd->padded_ram_size)) {
> -        mhd->standby_state_map[(unassign_addr -
> -                           mhd->padded_ram_size) / MEM_SECTION_SIZE] = 0;
> -
> -        /* find the specified memory region and destroy it */
> -        mr = memory_region_find(sysmem, unassign_addr, 1).mr;
> -        memory_region_unref(mr);
> -        if (mr) {
> -            int i;
> -            int is_removable = 1;
> -            ram_addr_t map_offset = (unassign_addr - mhd->padded_ram_size -
> -                                     (unassign_addr - mhd->padded_ram_size)
> -                                     % mhd->standby_subregion_size);
> -            /* Mark all affected subregions as 'standby' once again */
> -            for (i = 0;
> -                 i < (mhd->standby_subregion_size / MEM_SECTION_SIZE);
> -                 i++) {
> -
> -                if (mhd->standby_state_map[i + map_offset / 
> MEM_SECTION_SIZE]) {
> -                    is_removable = 0;
> -                    break;
> -                }
> -            }
> -            if (is_removable) {
> -                memory_region_del_subregion(sysmem, mr);
> -                object_unref(OBJECT(mr));
> -            }
> -        }
> -    }
> -    sccb->h.response_code = cpu_to_be16(SCLP_RC_NORMAL_COMPLETION);
> -}
> -
>  /* Provide information about the CPU */
>  static void sclp_read_cpu_info(SCLPDevice *sclp, SCCB *sccb)
>  {
> @@ -390,22 +168,6 @@ static void sclp_execute(SCLPDevice *sclp, SCCB *sccb, 
> uint32_t code)
>      case SCLP_CMDW_READ_CPU_INFO:
>          sclp_c->read_cpu_info(sclp, sccb);
>          break;
> -    case SCLP_READ_STORAGE_ELEMENT_INFO:
> -        if (code & 0xff00) {
> -            sclp_c->read_storage_element1_info(sclp, sccb);
> -        } else {
> -            sclp_c->read_storage_element0_info(sclp, sccb);
> -        }
> -        break;
> -    case SCLP_ATTACH_STORAGE_ELEMENT:
> -        sclp_c->attach_storage_element(sclp, sccb, (code & 0xff00) >> 8);
> -        break;
> -    case SCLP_ASSIGN_STORAGE:
> -        sclp_c->assign_storage(sclp, sccb);
> -        break;
> -    case SCLP_UNASSIGN_STORAGE:
> -        sclp_c->unassign_storage(sclp, sccb);
> -        break;
>      case SCLP_CMDW_CONFIGURE_IOA:
>          sclp_configure_io_adapter(sclp, sccb, true);
>          break;
> @@ -540,9 +302,6 @@ static void sclp_memory_init(SCLPDevice *sclp)
>  {
>      MachineState *machine = MACHINE(qdev_get_machine());
>      ram_addr_t initial_mem = machine->ram_size;
> -    ram_addr_t max_mem = machine->maxram_size;
> -    ram_addr_t standby_mem = max_mem - initial_mem;
> -    ram_addr_t pad_mem = 0;
>      int increment_size = 20;
> 
>      /* The storage increment size is a multiple of 1M and is a power of 2.
> @@ -552,34 +311,14 @@ static void sclp_memory_init(SCLPDevice *sclp)
>      while ((initial_mem >> increment_size) > MAX_STORAGE_INCREMENTS) {
>          increment_size++;
>      }
> -    if (machine->ram_slots) {
> -        while ((standby_mem >> increment_size) > MAX_STORAGE_INCREMENTS) {
> -            increment_size++;
> -        }
> -    }
>      sclp->increment_size = increment_size;
> 
> -    /* The core and standby memory areas need to be aligned with
> -     * the increment size.  In effect, this can cause the
> -     * user-specified memory size to be rounded down to align
> -     * with the nearest increment boundary. */
> +    /* The core memory area needs to be aligned with the increment size.
> +     * In effect, this can cause the user-specified memory size to be rounded
> +     * down to align with the nearest increment boundary. */
>      initial_mem = initial_mem >> increment_size << increment_size;
> -    standby_mem = standby_mem >> increment_size << increment_size;
> -
> -    /* If the size of ram is not on a MEM_SECTION_SIZE boundary,
> -       calculate the pad size necessary to force this boundary. */
> -    if (machine->ram_slots && standby_mem) {
> -        sclpMemoryHotplugDev *mhd = init_sclp_memory_hotplug_dev();
> 
> -        if (initial_mem % MEM_SECTION_SIZE) {
> -            pad_mem = MEM_SECTION_SIZE - initial_mem % MEM_SECTION_SIZE;
> -        }
> -        mhd->increment_size = increment_size;
> -        mhd->pad_size = pad_mem;
> -        mhd->standby_mem_size = standby_mem;
> -    }
>      machine->ram_size = initial_mem;
> -    machine->maxram_size = initial_mem + pad_mem + standby_mem;
>      /* let's propagate the changed ram size into the global variable. */
>      ram_size = initial_mem;
>  }
> @@ -613,11 +352,6 @@ static void sclp_class_init(ObjectClass *oc, void *data)
>      dc->user_creatable = false;
> 
>      sc->read_SCP_info = read_SCP_info;
> -    sc->read_storage_element0_info = read_storage_element0_info;
> -    sc->read_storage_element1_info = read_storage_element1_info;
> -    sc->attach_storage_element = attach_storage_element;
> -    sc->assign_storage = assign_storage;
> -    sc->unassign_storage = unassign_storage;
>      sc->read_cpu_info = sclp_read_cpu_info;
>      sc->execute = sclp_execute;
>      sc->service_interrupt = service_interrupt;
> @@ -632,42 +366,8 @@ static TypeInfo sclp_info = {
>      .class_size = sizeof(SCLPDeviceClass),
>  };
> 
> -sclpMemoryHotplugDev *init_sclp_memory_hotplug_dev(void)
> -{
> -    DeviceState *dev;
> -    dev = qdev_create(NULL, TYPE_SCLP_MEMORY_HOTPLUG_DEV);
> -    object_property_add_child(qdev_get_machine(),
> -                              TYPE_SCLP_MEMORY_HOTPLUG_DEV,
> -                              OBJECT(dev), NULL);
> -    qdev_init_nofail(dev);
> -    return SCLP_MEMORY_HOTPLUG_DEV(object_resolve_path(
> -                                   TYPE_SCLP_MEMORY_HOTPLUG_DEV, NULL));
> -}
> -
> -sclpMemoryHotplugDev *get_sclp_memory_hotplug_dev(void)
> -{
> -    return SCLP_MEMORY_HOTPLUG_DEV(object_resolve_path(
> -                                   TYPE_SCLP_MEMORY_HOTPLUG_DEV, NULL));
> -}
> -
> -static void sclp_memory_hotplug_dev_class_init(ObjectClass *klass,
> -                                               void *data)
> -{
> -    DeviceClass *dc = DEVICE_CLASS(klass);
> -
> -    set_bit(DEVICE_CATEGORY_MISC, dc->categories);
> -}
> -
> -static TypeInfo sclp_memory_hotplug_dev_info = {
> -    .name = TYPE_SCLP_MEMORY_HOTPLUG_DEV,
> -    .parent = TYPE_SYS_BUS_DEVICE,
> -    .instance_size = sizeof(sclpMemoryHotplugDev),
> -    .class_init = sclp_memory_hotplug_dev_class_init,
> -};
> -
>  static void register_types(void)
>  {
> -    type_register_static(&sclp_memory_hotplug_dev_info);
>      type_register_static(&sclp_info);
>  }
>  type_init(register_types);
> diff --git a/include/hw/s390x/sclp.h b/include/hw/s390x/sclp.h
> index 847ff32f85..476cbf78f2 100644
> --- a/include/hw/s390x/sclp.h
> +++ b/include/hw/s390x/sclp.h
> @@ -202,12 +202,6 @@ typedef struct SCLPDeviceClass {
>      /* private */
>      DeviceClass parent_class;
>      void (*read_SCP_info)(SCLPDevice *sclp, SCCB *sccb);
> -    void (*read_storage_element0_info)(SCLPDevice *sclp, SCCB *sccb);
> -    void (*read_storage_element1_info)(SCLPDevice *sclp, SCCB *sccb);
> -    void (*attach_storage_element)(SCLPDevice *sclp, SCCB *sccb,
> -                                   uint16_t element);
> -    void (*assign_storage)(SCLPDevice *sclp, SCCB *sccb);
> -    void (*unassign_storage)(SCLPDevice *sclp, SCCB *sccb);
>      void (*read_cpu_info)(SCLPDevice *sclp, SCCB *sccb);
> 
>      /* public */
> @@ -215,23 +209,6 @@ typedef struct SCLPDeviceClass {
>      void (*service_interrupt)(SCLPDevice *sclp, uint32_t sccb);
>  } SCLPDeviceClass;
> 
> -typedef struct sclpMemoryHotplugDev sclpMemoryHotplugDev;
> -
> -#define TYPE_SCLP_MEMORY_HOTPLUG_DEV "sclp-memory-hotplug-dev"
> -#define SCLP_MEMORY_HOTPLUG_DEV(obj) \
> -  OBJECT_CHECK(sclpMemoryHotplugDev, (obj), TYPE_SCLP_MEMORY_HOTPLUG_DEV)
> -
> -struct sclpMemoryHotplugDev {
> -    SysBusDevice parent;
> -    ram_addr_t standby_mem_size;
> -    ram_addr_t padded_ram_size;
> -    ram_addr_t pad_size;
> -    ram_addr_t standby_subregion_size;
> -    ram_addr_t rzm;
> -    int increment_size;
> -    char *standby_state_map;
> -};
> -
>  static inline int sccb_data_len(SCCB *sccb)
>  {
>      return be16_to_cpu(sccb->h.length) - sizeof(sccb->h);
> @@ -239,8 +216,6 @@ static inline int sccb_data_len(SCCB *sccb)
> 
> 
>  void s390_sclp_init(void);
> -sclpMemoryHotplugDev *init_sclp_memory_hotplug_dev(void);
> -sclpMemoryHotplugDev *get_sclp_memory_hotplug_dev(void);
>  void sclp_service_interrupt(uint32_t sccb);
>  void raise_irq_cpu_hotplug(void);
>  int sclp_service_call(CPUS390XState *env, uint64_t sccb, uint32_t code);
> diff --git a/target/s390x/cpu.h b/target/s390x/cpu.h
> index 14abcada31..80a0b49116 100644
> --- a/target/s390x/cpu.h
> +++ b/target/s390x/cpu.h
> @@ -627,7 +627,6 @@ QEMU_BUILD_BUG_ON(sizeof(SysIB) != 4096);
>  #define SIGP_ORDER_MASK 0x000000ff
> 
>  /* from s390-virtio-ccw */
> -#define MEM_SECTION_SIZE             0x10000000UL
>  #define MAX_AVAIL_SLOTS              32
> 
>  /* machine check interruption code */
>