Re: [PATCH v6 59/60] i386/cpu: Set up CPUID_HT in x86_cpu_realizefn() instead of cpu_x86_cpuid()

Xiaoyao Li
2024-11-05T09:33:39Z

On 11/5/2024 5:12 PM, Paolo Bonzini wrote:
> On 11/5/24 07:24, Xiaoyao Li wrote:
>> Otherwise, it gets warnings like below when number of vcpus > 1:
>>
>>    warning: TDX enforces set the feature: CPUID.01H:EDX.ht [bit 28]
>>
>> This is because x86_confidential_guest_check_features() checks
>> env->features[] instead of the cpuid date set up by cpu_x86_cpuid()
>>
>> Signed-off-by: Xiaoyao Li <xiaoyao.li@intel.com>
>> ---
>>   target/i386/cpu.c | 11 ++++++++++-
>>   1 file changed, 10 insertions(+), 1 deletion(-)
>>
>> diff --git a/target/i386/cpu.c b/target/i386/cpu.c
>> index 472ab206d8fe..214a1b00a815 100644
>> --- a/target/i386/cpu.c
>> +++ b/target/i386/cpu.c
>> @@ -6571,7 +6571,6 @@ void cpu_x86_cpuid(CPUX86State *env, uint32_t
>> index, uint32_t count,
>>           *edx = env->features[FEAT_1_EDX];
>>           if (threads_per_pkg > 1) {
>>               *ebx |= threads_per_pkg << 16;
>> -            *edx |= CPUID_HT;
>>           }
>>           if (!cpu->enable_pmu) {
>>               *ecx &= ~CPUID_EXT_PDCM;
>> @@ -7784,6 +7783,8 @@ static void x86_cpu_realizefn(DeviceState *dev,
>> Error **errp)
>>       Error *local_err = NULL;
>>       unsigned requested_lbr_fmt;
>> +    qemu_early_init_vcpu(cs);
>> +
>>   #if defined(CONFIG_TCG) && !defined(CONFIG_USER_ONLY)
>>       /* Use pc-relative instructions in system-mode */
>>       tcg_cflags_set(cs, CF_PCREL);
>> @@ -7851,6 +7852,14 @@ static void x86_cpu_realizefn(DeviceState *dev,
>> Error **errp)
>>           }
>>       }
>> +    /*
>> +     * It needs to called after feature filter because KVM doesn't
>> report HT
>> +     * as supported
>
> Does it, since kvm_arch_get_supported_cpuid() has the following line?
>
>     if (function == 1 && reg == R_EDX) {
>         ...
>         /* KVM never reports CPUID_HT but QEMU can support when vcpus >
> 1 */
>         ret |= CPUID_HT;
>
> ?

It seems I mixed it up with no_autoenable_flags. /faceplam

CPUID_HT doesn't get enabled by x86_cpu_expand_features() for "-cpu
host/max". It won't be filtered by x86_cpu_filter_features() either
because QEMU sets it in kvm_arch_get_supported_cpuid().

yes, the comment is wrong and comment needs to be dropped. The code can
be move up to just below x86_cpu_expand_features() or inside it?

> Paolo
>
>> +     */
>> +    if (cs->nr_cores * cs->nr_threads > 1) {
>> +        env->features[FEAT_1_EDX] |= CPUID_HT;
>> +    }
>