Re: [PATCH v3 3/3] KVM: x86: Move MPK feature detection to common code

[Babu Moger]

On 5/12/20 12:28 PM, Sean Christopherson wrote:
> On Tue, May 12, 2020 at 09:58:19AM -0700, Jim Mattson wrote:
>> On Tue, May 12, 2020 at 8:12 AM Babu Moger <babu.moger@xxxxxxx> wrote:
>>>
>>>
>>>
>>> On 5/11/20 6:51 PM, Jim Mattson wrote:
>>>> On Mon, May 11, 2020 at 4:33 PM Babu Moger <babu.moger@xxxxxxx> wrote:
>>>>>
>>>>> Both Intel and AMD support (MPK) Memory Protection Key feature.
>>>>> Move the feature detection from VMX to the common code. It should
>>>>> work for both the platforms now.
>>>>>
>>>>> Signed-off-by: Babu Moger <babu.moger@xxxxxxx>
>>>>> ---
>>>>>  arch/x86/kvm/cpuid.c   |    4 +++-
>>>>>  arch/x86/kvm/vmx/vmx.c |    4 ----
>>>>>  2 files changed, 3 insertions(+), 5 deletions(-)
>>>>>
>>>>> diff --git a/arch/x86/kvm/cpuid.c b/arch/x86/kvm/cpuid.c
>>>>> index 901cd1fdecd9..3da7d6ea7574 100644
>>>>> --- a/arch/x86/kvm/cpuid.c
>>>>> +++ b/arch/x86/kvm/cpuid.c
>>>>> @@ -278,6 +278,8 @@ void kvm_set_cpu_caps(void)
>>>>>  #ifdef CONFIG_X86_64
>>>>>         unsigned int f_gbpages = F(GBPAGES);
>>>>>         unsigned int f_lm = F(LM);
>>>>> +       /* PKU is not yet implemented for shadow paging. */
>>>>> +       unsigned int f_pku = tdp_enabled ? F(PKU) : 0;
>>>>
>>>> I think we still want to require that OSPKE be set on the host before
>>>> exposing PKU to the guest.
>>>>
>>>
>>> Ok I can add this check.
>>>
>>> +       unsigned int f_pku = tdp_enabled && F(OSPKE)? F(PKU) : 0;
>>
>> That doesn't do what you think it does. F(OSPKE) is a non-zero
>> constant, so that conjunct is always true.
> 
> My vote would be to omit f_pku and adjust the cap directly, e.g.

Sure. I am fine with this. Thanks

> 
> diff --git a/arch/x86/kvm/cpuid.c b/arch/x86/kvm/cpuid.c
> index 6828be99b9083..998c902df9e57 100644
> --- a/arch/x86/kvm/cpuid.c
> +++ b/arch/x86/kvm/cpuid.c
> @@ -326,7 +326,7 @@ void kvm_set_cpu_caps(void)
>         );
> 
>         kvm_cpu_cap_mask(CPUID_7_ECX,
> -               F(AVX512VBMI) | F(LA57) | 0 /*PKU*/ | 0 /*OSPKE*/ | F(RDPID) |
> +               F(AVX512VBMI) | F(LA57) | F(PKU) | 0 /*OSPKE*/ | F(RDPID) |
>                 F(AVX512_VPOPCNTDQ) | F(UMIP) | F(AVX512_VBMI2) | F(GFNI) |
>                 F(VAES) | F(VPCLMULQDQ) | F(AVX512_VNNI) | F(AVX512_BITALG) |
>                 F(CLDEMOTE) | F(MOVDIRI) | F(MOVDIR64B) | 0 /*WAITPKG*/
> @@ -334,6 +334,8 @@ void kvm_set_cpu_caps(void)
>         /* Set LA57 based on hardware capability. */
>         if (cpuid_ecx(7) & F(LA57))
>                 kvm_cpu_cap_set(X86_FEATURE_LA57);
> +       if (!tdp_enabled || !boot_cpu_has(OSPKE))
> +               kvm_cpu_cap_clear(X86_FEATURE_PKU);
> 
>         kvm_cpu_cap_mask(CPUID_7_EDX,
>                 F(AVX512_4VNNIW) | F(AVX512_4FMAPS) | F(SPEC_CTRL) |
>