Re: [Xen-devel] [PATCH v2 1/2] x86/hvm: allow guest to use clflushopt and clwb

["Jan Beulich" <JBeulich@xxxxxxxx>]

>>> On 07.01.16 at 15:01, <andrew.cooper3@xxxxxxxxxx> wrote:
> On 07/01/16 13:49, Jan Beulich wrote:
>>>>> On 30.12.15 at 12:48, <haozhong.zhang@xxxxxxxxx> wrote:
>>> --- a/xen/arch/x86/hvm/hvm.c
>>> +++ b/xen/arch/x86/hvm/hvm.c
>>> @@ -4583,21 +4583,30 @@ void hvm_cpuid(unsigned int input, unsigned int 
>>> *eax, 
> unsigned int *ebx,
>>>              *edx &= ~cpufeat_mask(X86_FEATURE_PSE36);
>>>          break;
>>>      case 0x7:
>>> -        if ( (count == 0) && !cpu_has_smep )
>>> -            *ebx &= ~cpufeat_mask(X86_FEATURE_SMEP);
>>> +        if ( count == 0 )
>>> +        {
>>> +            if ( !cpu_has_smep )
>>> +                *ebx &= ~cpufeat_mask(X86_FEATURE_SMEP);
>>> +
>>> +            if ( !cpu_has_smap )
>>> +                *ebx &= ~cpufeat_mask(X86_FEATURE_SMAP);
>>> +
>>> +            /* Don't expose MPX to hvm when VMX support is not available */
>>> +            if ( !(vmx_vmexit_control & VM_EXIT_CLEAR_BNDCFGS) ||
>>> +                 !(vmx_vmentry_control & VM_ENTRY_LOAD_BNDCFGS) )
>>> +                *ebx &= ~cpufeat_mask(X86_FEATURE_MPX);
>>>  
>>> -        if ( (count == 0) && !cpu_has_smap )
>>> -            *ebx &= ~cpufeat_mask(X86_FEATURE_SMAP);
>>> +            /* Don't expose INVPCID to non-hap hvm. */
>>> +            if ( !hap_enabled(d) )
>>> +                *ebx &= ~cpufeat_mask(X86_FEATURE_INVPCID);
>>>  
>>> -        /* Don't expose MPX to hvm when VMX support is not available */
>>> -        if ( (count == 0) &&
>>> -             (!(vmx_vmexit_control & VM_EXIT_CLEAR_BNDCFGS) ||
>>> -              !(vmx_vmentry_control & VM_ENTRY_LOAD_BNDCFGS)) )
>>> -            *ebx &= ~cpufeat_mask(X86_FEATURE_MPX);
>>> +            if ( !cpu_has_clflushopt )
>>> +                *ebx &= ~cpufeat_mask(X86_FEATURE_CLFLUSHOPT);
>>> +
>>> +            if ( !cpu_has_clwb )
>>> +                *ebx &= ~cpufeat_mask(X86_FEATURE_CLWB);
>> I don't think we need this: Other than other things adjusted here,
>> there's nothing disabling these two features when found available,
>> and there are no extra conditions to consider. Otherwise, if we
>> were to follow this route, quite a bit of code would need to be
>> added to other case statements in this function. But that's all (I
>> think) going to be taken care of by Andrew's CPUID leveling series.
> 
> My series does take care of all of this.
> 
> I would prefer that these two changes get taken as soon as they are
> ready, so I can rebase.

If we don't need the change quoted above, your rebase will actually
be easier to do.

Jan


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