Re: [PATCH-for-9.0 v2] hw/i386/pc: Deprecate 64-bit CPUs on ISA-only PC machine

On 28/03/2024 16.12, Mark Cave-Ayland wrote: > On 27/03/2024 16:54, Philippe Mathieu-Daudé wrote: > >> Per Daniel suggestion [*]: >> >>   > isapc could arguably be restricted to just 32-bit CPU models, >>   > because we should not need it to support any feature that didn't >>   > exist prior to circa 1995. eg refuse to start with isapc, if 'lm' >>   > is present in the CPU model for example. >> >> Display a warning when such CPU is used: >> >>    $ qemu-system-x86_64 -monitor stdio -S -M isapc -cpu Westmere >>    qemu-system-x86_64: warning: Use of 64-bit CPU 'Westmere' is >> deprecated on the ISA-only PC machine >>    QEMU 8.2.91 monitor - type 'help' for more information >>    (qemu) q >> >>    $ qemu-system-x86_64 -monitor stdio -S -M isapc -cpu athlon >>    QEMU 8.2.91 monitor - type 'help' for more information >>    (qemu) q >> >> [*] https://lore.kernel.org/qemu-devel/ZgQkS4RPmSt5Xa08@redhat.com/ >> >> Suggested-by: Daniel P. Berrangé <berrange(a)redhat.com&gt; >> Signed-off-by: Philippe Mathieu-Daudé <philmd(a)linaro.org&gt; >> --- >>   docs/about/deprecated.rst |  7 +++++++ >>   include/hw/i386/pc.h      |  1 + >>   hw/i386/pc_piix.c         | 14 ++++++++++++++ >>   3 files changed, 22 insertions(+) >> >> diff --git a/docs/about/deprecated.rst b/docs/about/deprecated.rst >> index 7b548519b5..345c35507f 100644 >> --- a/docs/about/deprecated.rst >> +++ b/docs/about/deprecated.rst >> @@ -208,6 +208,13 @@ is no longer packaged in any distro making it >> harder to run the >>   ``check-tcg`` tests. Unless we can improve the testing situation there >>   is a chance the code will bitrot without anyone noticing. >> +64-bit (x86_64) CPUs on the ``isapc`` machine (since 9.0) >> +''''''''''''''''''''''''''''''''''''''''''''''''''''''''' >> + >> +The ``isapc`` machine aims to emulate old PC machine without PCI was >> +generalized, so hardware available around 1995, before 64-bit intel >> +CPUs were produced. >> + >>   System emulator machines >>   ------------------------ >> diff --git a/include/hw/i386/pc.h b/include/hw/i386/pc.h >> index 27a68071d7..2d202b9549 100644 >> --- a/include/hw/i386/pc.h >> +++ b/include/hw/i386/pc.h >> @@ -96,6 +96,7 @@ struct PCMachineClass { >>       const char *default_south_bridge; >>       /* Compat options: */ >> +    bool deprecate_64bit_cpu; /* Specific to the 'isapc' machine */ >>       /* Default CPU model version.  See >> x86_cpu_set_default_version(). */ >>       int default_cpu_version; >> diff --git a/hw/i386/pc_piix.c b/hw/i386/pc_piix.c >> index 18ba076609..2e5b2efc33 100644 >> --- a/hw/i386/pc_piix.c >> +++ b/hw/i386/pc_piix.c >> @@ -182,7 +182,20 @@ static void pc_init1(MachineState *machine, >> const char *pci_type) >>       } >>       pc_machine_init_sgx_epc(pcms); >> + >>       x86_cpus_init(x86ms, pcmc->default_cpu_version); >> +    if (pcmc->deprecate_64bit_cpu) { >> +        X86CPU *cpu = X86_CPU(first_cpu); >> + >> +        if (cpu->env.features[FEAT_8000_0001_EDX] & CPUID_EXT2_LM) { >> +            const char *cpu_type = >> object_get_typename(OBJECT(first_cpu)); >> +            int cpu_len = strlen(cpu_type) - >> strlen(X86_CPU_TYPE_SUFFIX); >> + >> +            warn_report("Use of 64-bit CPU '%.*s' is deprecated" >> +                        " on the ISA-only PC machine", >> +                        cpu_len, cpu_type); >> +        } >> +    } >>       if (kvm_enabled()) { >>           kvmclock_create(pcmc->kvmclock_create_always); >> @@ -918,6 +931,7 @@ static void isapc_machine_options(MachineClass *m) >>       pcmc->gigabyte_align = false; >>       pcmc->smbios_legacy_mode = true; >>       pcmc->has_reserved_memory = false; >> +    pcmc->deprecate_64bit_cpu = true; >>       m->default_nic = "ne2k_isa"; >>       m->default_cpu_type = X86_CPU_TYPE_NAME("486"); >>       m->no_parallel = !module_object_class_by_name(TYPE_ISA_PARALLEL); > > The logic around checking CPUID_EXT2_LM looks good to me. Slightly > curious as to whether people feel updating PCMachineClass is > necessary, or you can simply do qdev_get_machine() and use > object_dynamic_cast() to see if the machine matches > MACHINE_NAME("isapc") and warn that way? Why don't you simply pass it as a parameter from pc_init_isa() instead? Or do the whole check in pc_init_isa() instead?