Hi Zhao,
On 07-01-2026 13:17, Zhao Liu wrote:
> On Fri, Nov 21, 2025 at 08:34:49AM +0000, Shivansh Dhiman wrote:
>> diff --git a/target/i386/cpu.c b/target/i386/cpu.c
>> index b7827e448aa5..01c4da7cf134 100644
>> --- a/target/i386/cpu.c
>> +++ b/target/i386/cpu.c
>> @@ -9158,6 +9158,12 @@ void x86_cpu_expand_features(X86CPU *cpu, Error
>> **errp)
>> if (env->features[FEAT_7_0_EBX] & CPUID_7_0_EBX_SGX) {
>> x86_cpu_adjust_level(cpu, &env->cpuid_min_level, 0x12);
>> }
>> +
>> + /* Enable CPUID[0x80000026] for AMD Genoa models and above */
>> + if (cpu->force_cpuid_0x80000026 ||
>> + (!xcc->model && x86_is_amd_zen4_or_above(cpu))) {
>
> I understand you want to address max/host CPU case here, but it's still
> may not guarentee the compatibility with old QEMU PC mahinces, e.g.,
> boot a old PC machine on v11.0 QEMU, it can still have this leaf.
Wouldn't initializing x-force-cpuid-0x80000026 default to false prevent this?
Oh, but, this CPUID can still be enabled on an older machine-type with latest
QEMU with the existing checks. And probably this could also affect live
migration.
>
> So it would be better to add a compat option to disable 0x80000026 for
> old PC machines by default.
Does this look fine?
GlobalProperty pc_compat_10_2[] = {
{ TYPE_X86_CPU, "x-force-cpuid-0x80000026", "false" },
};
const size_t pc_compat_10_2_len = G_N_ELEMENTS(pc_compat_10_2);
>
> If needed, to avoid unnecessarily enabling extended CPU topology, I think
> it's possible to implement a check similar to x86_has_cpuid_0x1f().
Do you mean something like this? I avoided it initially because it is
functionally same as current one, and a bit lengthy.
/* Enable CPUID[0x80000026] for AMD Genoa models and above */
static inline bool x86_has_cpuid_0x80000026(X86CPU *cpu) {
X86CPUClass *xcc = X86_CPU_GET_CLASS(cpu);
return cpu->force_cpuid_0x80000026 ||
(!xcc->model && x86_is_amd_zen4_or_above(cpu));
}
...
if (x86_has_cpuid_0x80000026(cpu))
x86_cpu_adjust_level(cpu, &env->cpuid_min_xlevel, 0x80000026);
Thanks for the review.
Shivansh
>
>> + x86_cpu_adjust_level(cpu, &env->cpuid_min_xlevel, 0x80000026);
>> + }
>> }
>
> Thanks,
> Zhao
>
