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hw/i386/pc_piix.c: restrict isapc machine to 32-bit CPUs

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The isapc machine represents a legacy ISA PC with a 486 CPU. Whilst it is
possible to specify any CPU via -cpu on the command line, it makes no
sense to allow modern 64-bit CPUs to be used.

Restrict the isapc machine to the available 32-bit CPUs, taking care to
handle the case where if a user inadvertently uses either -cpu max or
-cpu host then the "best" 32-bit CPU is used (in this case the pentium3).

Signed-off-by: Mark Cave-Ayland <mark.caveayland@nutanix.com>
Reviewed-by: Philippe Mathieu-Daudé <philmd@linaro.org>
Link: https://lore.kernel.org/r/20250828111057.468712-2-mark.caveayland@nutanix.com
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
This commit is contained in:
Mark Cave-Ayland 2025-08-28 12:09:44 +01:00 • committed by Paolo Bonzini
parent 59f504bb43
commit e1e2909f8e
1 changed files with 39 additions and 0 deletions
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39
hw/i386/pc_piix.c
View file

@ -436,6 +436,31 @@ static void pc_set_south_bridge(Object *obj, int value, Error **errp)
#ifdef CONFIG_ISAPC
static void pc_init_isa(MachineState *machine)
{
/*
* There is a small chance that someone unintentionally passes "-cpu max"
* for the isapc machine, which will provide a much more modern 32-bit
* CPU than would be expected for an ISA-era PC. If the "max" cpu type has
* been specified, choose the "best" 32-bit cpu possible which we consider
* be the pentium3 (deliberately choosing an Intel CPU given that the
* default 486 CPU for the isapc machine is also an Intel CPU).
*/
if (!strcmp(machine->cpu_type, X86_CPU_TYPE_NAME("max"))) {
machine->cpu_type = X86_CPU_TYPE_NAME("pentium3");
warn_report("-cpu max is invalid for isapc machine, using pentium3");
}
/*
* Similarly if someone unintentionally passes "-cpu host" for the isapc
* machine then display a warning and also switch to the "best" 32-bit
* cpu possible which we consider to be the pentium3. This is because any
* host CPU will already be modern than this, but it also ensures any
* newer CPU flags/features are filtered out for older guests.
*/
if (!strcmp(machine->cpu_type, X86_CPU_TYPE_NAME("host"))) {
machine->cpu_type = X86_CPU_TYPE_NAME("pentium3");
warn_report("-cpu host is invalid for isapc machine, using pentium3");
}
pc_init1(machine, NULL);
}
#endif
@ -815,7 +840,20 @@ DEFINE_I440FX_MACHINE(2, 6);
#ifdef CONFIG_ISAPC
static void isapc_machine_options(MachineClass *m)
{
static const char * const valid_cpu_types[] = {
X86_CPU_TYPE_NAME("486"),
X86_CPU_TYPE_NAME("athlon"),
X86_CPU_TYPE_NAME("kvm32"),
X86_CPU_TYPE_NAME("pentium"),
X86_CPU_TYPE_NAME("pentium2"),
X86_CPU_TYPE_NAME("pentium3"),
X86_CPU_TYPE_NAME("qemu32"),
X86_CPU_TYPE_NAME("max"),
X86_CPU_TYPE_NAME("host"),
NULL
};
PCMachineClass *pcmc = PC_MACHINE_CLASS(m);
m->desc = "ISA-only PC";
m->max_cpus = 1;
m->option_rom_has_mr = true;
@ -828,6 +866,7 @@ static void isapc_machine_options(MachineClass *m)
pcmc->has_reserved_memory = false;
m->default_nic = "ne2k_isa";
m->default_cpu_type = X86_CPU_TYPE_NAME("486");
m->valid_cpu_types = valid_cpu_types;
m->no_floppy = !module_object_class_by_name(TYPE_ISA_FDC);
m->no_parallel = !module_object_class_by_name(TYPE_ISA_PARALLEL);
}