Re: [PATCH V2 3/3] target/i386: Move host_cpu_enable_cpu_pm into kvm_cpu_realizefn()

[Chen, Zide]

On 5/30/2024 11:53 PM, Zhao Liu wrote:
> On Fri, May 24, 2024 at 01:00:17PM -0700, Zide Chen wrote:
>> Date: Fri, 24 May 2024 13:00:17 -0700
>> From: Zide Chen <zide.chen@intel.com>
>> Subject: [PATCH V2 3/3] target/i386: Move host_cpu_enable_cpu_pm into
>>  kvm_cpu_realizefn()
>> X-Mailer: git-send-email 2.34.1
>>
>> It seems not a good idea to expand features in host_cpu_realizefn,
>> which is for host CPU only. 
> 
> It is restricted by max_features and should be part of the "max" CPU,
> and the current target/i386/host-cpu.c should only serve the “host” CPU.

Yes, since this file only serves for "host" CPU, that's why I proposed
to move this code to kvm_cpu_realizefn().

> 
>> Additionally, cpu-pm option is KVM
>> specific, and it's cleaner to put it in kvm_cpu_realizefn(), together
>> with the WAITPKG code.
>>
>> Fixes: f5cc5a5c1686 ("i386: split cpu accelerators from cpu.c, using 
>> AccelCPUClass")
>> Signed-off-by: Zide Chen <zide.chen@intel.com>
>> ---
>>  target/i386/host-cpu.c    | 12 ------------
>>  target/i386/kvm/kvm-cpu.c | 11 +++++++++--
>>  2 files changed, 9 insertions(+), 14 deletions(-)
>>
>> diff --git a/target/i386/host-cpu.c b/target/i386/host-cpu.c
>> index 280e427c017c..8b8bf5afeccf 100644
>> --- a/target/i386/host-cpu.c
>> +++ b/target/i386/host-cpu.c
>> @@ -42,15 +42,6 @@ static uint32_t host_cpu_phys_bits(void)
>>      return host_phys_bits;
>>  }
>>  
>> -static void host_cpu_enable_cpu_pm(X86CPU *cpu)
>> -{
>> -    CPUX86State *env = &cpu->env;
>> -
>> -    host_cpuid(5, 0, &cpu->mwait.eax, &cpu->mwait.ebx,
>> -               &cpu->mwait.ecx, &cpu->mwait.edx);
>> -    env->features[FEAT_1_ECX] |= CPUID_EXT_MONITOR;
>> -}
>> -
>>  static uint32_t host_cpu_adjust_phys_bits(X86CPU *cpu)
>>  {
>>      uint32_t host_phys_bits = host_cpu_phys_bits();
>> @@ -83,9 +74,6 @@ bool host_cpu_realizefn(CPUState *cs, Error **errp)
>>      X86CPU *cpu = X86_CPU(cs);
>>      CPUX86State *env = &cpu->env;
>>  
>> -    if (cpu->max_features && enable_cpu_pm) {
>> -        host_cpu_enable_cpu_pm(cpu);
>> -    }
>>      if (env->features[FEAT_8000_0001_EDX] & CPUID_EXT2_LM) {
>>          uint32_t phys_bits = host_cpu_adjust_phys_bits(cpu);
>>  
>> diff --git a/target/i386/kvm/kvm-cpu.c b/target/i386/kvm/kvm-cpu.c
>> index 3adcedf0dbc3..197c892da89a 100644
>> --- a/target/i386/kvm/kvm-cpu.c
>> +++ b/target/i386/kvm/kvm-cpu.c
>> @@ -64,9 +64,16 @@ static bool kvm_cpu_realizefn(CPUState *cs, Error **errp)
>>       *   cpu_common_realizefn() (via xcc->parent_realize)
>>       */
>>      if (cpu->max_features) {
>> -        if (enable_cpu_pm && kvm_has_waitpkg()) {
>> -            env->features[FEAT_7_0_ECX] |= CPUID_7_0_ECX_WAITPKG;
>> +        if (enable_cpu_pm) {
>> +            if (kvm_has_waitpkg()) {
>> +                env->features[FEAT_7_0_ECX] |= CPUID_7_0_ECX_WAITPKG;
>> +            }
> 
> If you agree with my comment in patch 2, here we need a mwait bit check.

I still think that take advantaged of x86_cpu_filter_features() to check
host availability is a better choice.

> 
>> +            host_cpuid(5, 0, &cpu->mwait.eax, &cpu->mwait.ebx,
>> +                       &cpu->mwait.ecx, &cpu->mwait.edx);
>> +            env->features[FEAT_1_ECX] |= CPUID_EXT_MONITOR;
>>          }
>> +
>>          if (cpu->ucode_rev == 0) {
>>              cpu->ucode_rev =
>>                  kvm_arch_get_supported_msr_feature(kvm_state,
>> -- 
>> 2.34.1
>>
>>