Re: [PATCH v1] vl/s390: fixup ram sizes for compat machines

[Cornelia Huck <cohuck@redhat.com>]

On Tue, 31 Mar 2020 11:35:54 -0400
Christian Borntraeger <borntraeger@de.ibm.com> wrote:

> compat machines did fixup the ram size to match what can be reported via

s/compat machines/Older QEMU versions/ ?

> sclp. We need to mimic those for machines 4.2 and older to not fail on

"We need to mimic this behavior for machine types 4.2 and older" ?

> inbound migration. For Machines >= 5.0 we can simply use an increment

s/Machines/machine types/

> size of 1M und use the full range of increment number which allows for
> all possible memory sizes. The old limitation of having a maximum of
> 1020 increments was added for standby memory, which we no longer
> support. With that we can now support even weird memory sizes like
> 10001234 MB.

FWIW, I think this approach is better than a hard fail of odd memory
sizes, even if we think now that the automatic rounding was not such a
good idea.

> 
> Fixes: 3a12fc61af5c ("390x/s390-virtio-ccw: use memdev for RAM")
> Reported-by: Lukáš Doktor <ldoktor@redhat.com>
> Cc: Igor Mammedov <imammedo@redhat.com>
> Cc: Dr. David Alan Gilbert <dgilbert@redhat.com>
> Signed-off-by: David Hildenbrand <david@redhat.com>
> Signed-off-by: Christian Borntraeger <borntraeger@de.ibm.com>
> ---
> RFC->v1:
> - also fix mamram
> - provide full granularity for machine 5.0
> 
>  hw/s390x/s390-skeys.c              |  2 +-
>  hw/s390x/s390-stattrib-kvm.c       |  4 ++--
>  hw/s390x/s390-virtio-ccw.c         | 20 ++++++++++++++++++++
>  hw/s390x/sclp.c                    | 19 ++++++-------------
>  include/hw/boards.h                |  1 +
>  include/hw/s390x/s390-virtio-ccw.h |  4 +++-
>  softmmu/vl.c                       |  3 +++
>  7 files changed, 36 insertions(+), 17 deletions(-)
> 

(...)

> diff --git a/hw/s390x/s390-virtio-ccw.c b/hw/s390x/s390-virtio-ccw.c
> index 3cf19c99f3..bdfd10f77d 100644
> --- a/hw/s390x/s390-virtio-ccw.c
> +++ b/hw/s390x/s390-virtio-ccw.c
> @@ -579,6 +579,16 @@ static void s390_nmi(NMIState *n, int cpu_index, Error **errp)
>      s390_cpu_restart(S390_CPU(cs));
>  }
>  
> +static ram_addr_t s390_align_ram(ram_addr_t sz)
> +{
> +    /* same logic as in sclp.c */
> +    int increment_size = 20;
> +    while ((sz >> increment_size) > 1020) {

<nitpick>Use MAX_STORAGE_INCREMENTS?</nitpick>

> +        increment_size++;
> +    }
> +    return sz >> increment_size << increment_size;
> +}
> +
>  static void ccw_machine_class_init(ObjectClass *oc, void *data)
>  {
>      MachineClass *mc = MACHINE_CLASS(oc);
> @@ -590,6 +600,7 @@ static void ccw_machine_class_init(ObjectClass *oc, void *data)
>      s390mc->cpu_model_allowed = true;
>      s390mc->css_migration_enabled = true;
>      s390mc->hpage_1m_allowed = true;
> +    s390mc->mem_inc_1020 = false;
>      mc->init = ccw_init;
>      mc->reset = s390_machine_reset;
>      mc->hot_add_cpu = s390_hot_add_cpu;
> @@ -686,6 +697,11 @@ bool hpage_1m_allowed(void)
>      return get_machine_class()->hpage_1m_allowed;
>  }
>  
> +bool mem_inc_1020(void)
> +{
> +    return get_machine_class()->mem_inc_1020;

Not sure I like that name; but cannot think of a better name, either :(

> +}
> +
>  static char *machine_get_loadparm(Object *obj, Error **errp)
>  {
>      S390CcwMachineState *ms = S390_CCW_MACHINE(obj);
> @@ -807,7 +823,11 @@ static void ccw_machine_4_2_instance_options(MachineState *machine)
>  
>  static void ccw_machine_4_2_class_options(MachineClass *mc)
>  {
> +    S390CcwMachineClass *s390mc = S390_MACHINE_CLASS(mc);
> +
>      ccw_machine_5_0_class_options(mc);
> +    mc->machine_align_ram = s390_align_ram;
> +    s390mc->mem_inc_1020 = true;
>      compat_props_add(mc->compat_props, hw_compat_4_2, hw_compat_4_2_len);
>  }
>  DEFINE_CCW_MACHINE(4_2, "4.2", false);
> diff --git a/hw/s390x/sclp.c b/hw/s390x/sclp.c
> index d8ae207731..d1fff18443 100644
> --- a/hw/s390x/sclp.c
> +++ b/hw/s390x/sclp.c
> @@ -21,6 +21,7 @@
>  #include "hw/s390x/sclp.h"
>  #include "hw/s390x/event-facility.h"
>  #include "hw/s390x/s390-pci-bus.h"
> +#include "hw/s390x/s390-virtio-ccw.h"
>  #include "hw/s390x/ipl.h"
>  
>  static inline SCLPDevice *get_sclp_device(void)
> @@ -346,7 +347,7 @@ static void sclp_realize(DeviceState *dev, Error **errp)
>       */
>      qdev_set_parent_bus(DEVICE(sclp->event_facility), sysbus_get_default());
>  
> -    ret = s390_set_memory_limit(machine->maxram_size, &hw_limit);
> +    ret = s390_set_memory_limit(machine->ram_size, &hw_limit);
>      if (ret == -E2BIG) {
>          error_setg(&err, "host supports a maximum of %" PRIu64 " GB",
>                     hw_limit / GiB);
> @@ -365,23 +366,15 @@ static void sclp_memory_init(SCLPDevice *sclp)
>      int increment_size = 20;
>  
>      /* The storage increment size is a multiple of 1M and is a power of 2.
> -     * The number of storage increments must be MAX_STORAGE_INCREMENTS or fewer.
> +     * The number of storage increments must be MAX_STORAGE_INCREMENTS or fewer
> +     * for some machine types.

I think

"For some machine types, the number of..."

would read a bit better.

>       * The variable 'increment_size' is an exponent of 2 that can be
>       * used to calculate the size (in bytes) of an increment. */
> -    while ((initial_mem >> increment_size) > MAX_STORAGE_INCREMENTS) {
> +    while (mem_inc_1020() &&
> +           (initial_mem >> increment_size) > MAX_STORAGE_INCREMENTS) {
>          increment_size++;
>      }
>      sclp->increment_size = increment_size;
> -
> -    /* 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;
> -
> -    machine->ram_size = initial_mem;
> -    machine->maxram_size = initial_mem;
> -    /* let's propagate the changed ram size into the global variable. */
> -    ram_size = initial_mem;
>  }
>  
>  static void sclp_init(Object *obj)
> diff --git a/include/hw/boards.h b/include/hw/boards.h
> index 236d239c19..e3574f4b5f 100644
> --- a/include/hw/boards.h
> +++ b/include/hw/boards.h
> @@ -218,6 +218,7 @@ struct MachineClass {
>                                                           unsigned cpu_index);
>      const CPUArchIdList *(*possible_cpu_arch_ids)(MachineState *machine);
>      int64_t (*get_default_cpu_node_id)(const MachineState *ms, int idx);
> +    ram_addr_t (*machine_align_ram)(ram_addr_t size);

/* Intended for compatibility handling. */ ?

>  };
>  
>  /**

(...)

Apart from the nits, looks sane to me.