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

["Jan Beulich" <JBeulich@xxxxxxxx>]

>>> On 08.01.16 at 09:27, <haozhong.zhang@xxxxxxxxx> wrote:
> On 01/07/16 07:34, Jan Beulich wrote:
>> >>> 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.
>>
> I'll remove changes in hvm_cpuid() in the next version. Changes in
> xen/include/asm-x86/cpufeature.h will be removed as well, because
> there will be no use of them.

Indeed - this should become a tools only patch.

Jan


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