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

["Philippe Mathieu-Daudé" <philmd@linaro.org>]

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?

> +    depends on S390X