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

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?