Re: [PULL 11/11] target/s390x: Add a CONFIG switch to disable legacy CPUs

[Thomas Huth <thuth@redhat.com>]

On 07/03/2025 16.27, Philippe Mathieu-Daudé wrote:
> Hi Thomas,
> 
> On 24/6/24 11:10, Thomas Huth wrote:
>> The oldest model that IBM still supports is the z13. Considering
>> that each generation can "emulate" the previous two generations
>> in hardware (via the "IBC" feature of the CPUs), this means that
>> everything that is older than z114/196 is not an officially supported
>> CPU model anymore. The Linux kernel still support the z10, so if
>> we also take this into account, everything older than that can
>> definitely be considered as a legacy CPU model.
>>
>> For downstream builds of QEMU, we would like to be able to disable
>> these legacy CPUs in the build. Thus add a CONFIG switch that can be
>> used to disable them (and old machine types that use them by default).
>>
>> Message-Id: <20240614125019.588928-1-thuth@redhat.com>
>> Signed-off-by: Thomas Huth <thuth@redhat.com>
>> ---
>>   hw/s390x/s390-virtio-ccw.c | 5 +++++
>>   target/s390x/cpu_models.c  | 9 +++++++++
>>   target/s390x/Kconfig       | 5 +++++
>>   3 files changed, 19 insertions(+)
>>
>> diff --git a/hw/s390x/s390-virtio-ccw.c b/hw/s390x/s390-virtio-ccw.c
>> index 3d0bc3e7f2..cd063f8b64 100644
>> --- a/hw/s390x/s390-virtio-ccw.c
>> +++ b/hw/s390x/s390-virtio-ccw.c
>> @@ -47,6 +47,7 @@
>>   #include "migration/blocker.h"
>>   #include "qapi/visitor.h"
>>   #include "hw/s390x/cpu-topology.h"
>> +#include CONFIG_DEVICES
>>   static Error *pv_mig_blocker;
>> @@ -1126,6 +1127,8 @@ static void 
>> ccw_machine_2_12_class_options(MachineClass *mc)
>>   }
>>   DEFINE_CCW_MACHINE(2_12, "2.12", false);
>> +#ifdef CONFIG_S390X_LEGACY_CPUS
>> +
>>   static void ccw_machine_2_11_instance_options(MachineState *machine)
>>   {
>>       static const S390FeatInit qemu_cpu_feat = 
>> { S390_FEAT_LIST_QEMU_V2_11 };
>> @@ -1272,6 +1275,8 @@ static void 
>> ccw_machine_2_4_class_options(MachineClass *mc)
>>   }
>>   DEFINE_CCW_MACHINE(2_4, "2.4", false);
>> +#endif
>> +
>>   static void ccw_machine_register_types(void)
>>   {
>>       type_register_static(&ccw_machine_info);
>> diff --git a/target/s390x/cpu_models.c b/target/s390x/cpu_models.c
>> index efb508cd2e..a27f4b6f79 100644
>> --- a/target/s390x/cpu_models.c
>> +++ b/target/s390x/cpu_models.c
>> @@ -25,6 +25,7 @@
>>   #ifndef CONFIG_USER_ONLY
>>   #include "sysemu/sysemu.h"
>>   #include "target/s390x/kvm/pv.h"
>> +#include CONFIG_DEVICES
>>   #endif
>>   #define CPUDEF_INIT(_type, _gen, _ec_ga, _mha_pow, _hmfai, _name, _desc) \
>> @@ -47,6 +48,13 @@
>>    * generation 15 one base feature and one optional feature have been 
>> deprecated.
>>    */
>>   static S390CPUDef s390_cpu_defs[] = {
>> +    /*
>> +     * Linux requires at least z10 nowadays, and IBM only supports recent 
>> CPUs
>> +     * (see https://www.ibm.com/support/pages/ibm-mainframe-life-cycle- 
>> history),
>> +     * so we consider older CPUs as legacy that can optionally be 
>> disabled via
>> +     * the CONFIG_S390X_LEGACY_CPUS config switch.
>> +     */
>> +#if defined(CONFIG_S390X_LEGACY_CPUS) || defined(CONFIG_USER_ONLY)
>>       CPUDEF_INIT(0x2064, 7, 1, 38, 0x00000000U, "z900", "IBM zSeries 900 
>> GA1"),
>>       CPUDEF_INIT(0x2064, 7, 2, 38, 0x00000000U, "z900.2", "IBM zSeries 
>> 900 GA2"),
>>       CPUDEF_INIT(0x2064, 7, 3, 38, 0x00000000U, "z900.3", "IBM zSeries 
>> 900 GA3"),
>> @@ -64,6 +72,7 @@ static S390CPUDef s390_cpu_defs[] = {
>>       CPUDEF_INIT(0x2096, 9, 2, 40, 0x00000000U, "z9BC", "IBM System z9 BC 
>> GA1"),
>>       CPUDEF_INIT(0x2094, 9, 3, 40, 0x00000000U, "z9EC.3", "IBM System z9 
>> EC GA3"),
>>       CPUDEF_INIT(0x2096, 9, 3, 40, 0x00000000U, "z9BC.2", "IBM System z9 
>> BC GA2"),
>> +#endif
>>       CPUDEF_INIT(0x2097, 10, 1, 43, 0x00000000U, "z10EC", "IBM System z10 
>> EC GA1"),
>>       CPUDEF_INIT(0x2097, 10, 2, 43, 0x00000000U, "z10EC.2", "IBM System 
>> z10 EC GA2"),
>>       CPUDEF_INIT(0x2098, 10, 2, 43, 0x00000000U, "z10BC", "IBM System z10 
>> BC GA1"),
>> diff --git a/target/s390x/Kconfig b/target/s390x/Kconfig
>> index d886be48b4..8a95f2bc3f 100644
>> --- a/target/s390x/Kconfig
>> +++ b/target/s390x/Kconfig
>> @@ -2,3 +2,8 @@ config S390X
>>       bool
>>       select PCI
>>       select S390_FLIC
>> +
>> +config S390X_LEGACY_CPUS
>> +    bool
>> +    default y
> 
> Do we have plan to deprecate or switch that off?

No, this is mainly a config knob for downstream builds that do not want to 
include legacy CPUs, but for upstream it should be fine to keep those around.

Why do you ask?

  Thomas