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

[Sean Christopherson]

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.

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) |