Re: [RFC 6/7] KVM: X86: Expose PKS to guest and userspace

[Chenyi Qiang]

On 8/14/2020 3:04 AM, Jim Mattson wrote:
> On Fri, Aug 7, 2020 at 1:47 AM Chenyi Qiang <chenyi.qiang@xxxxxxxxx> wrote:
> > Existence of PKS is enumerated via CPUID.(EAX=7H,ECX=0):ECX[31]. It is
> > enabled by setting CR4.PKS when long mode is active. PKS is only
> > implemented when EPT is enabled and requires the support of VM_{ENTRY,
> > EXIT}_LOAD_IA32_PKRS currently.
> >
> > Signed-off-by: Chenyi Qiang <chenyi.qiang@xxxxxxxxx>
>
> > @@ -967,7 +969,8 @@ int kvm_set_cr4(struct kvm_vcpu *vcpu, unsigned long cr4)
> >   {
> >          unsigned long old_cr4 = kvm_read_cr4(vcpu);
> >          unsigned long pdptr_bits = X86_CR4_PGE | X86_CR4_PSE | X86_CR4_PAE |
> > -                                  X86_CR4_SMEP | X86_CR4_SMAP | X86_CR4_PKE;
> > +                                  X86_CR4_SMEP | X86_CR4_SMAP | X86_CR4_PKE |
> > +                                  X86_CR4_PKS;
>
> This list already seems overly long, but I don't think CR4.PKS belongs
> here. In volume 3 of the SDM, section 4.4.1, it says:
>
> - If PAE paging would be in use following an execution of MOV to CR0
> or MOV to CR4 (see Section 4.1.1) and the instruction is modifying any
> of CR0.CD, CR0.NW, CR0.PG, CR4.PAE, CR4.PGE, CR4.PSE, or CR4.SMEP;
> then the PDPTEs are loaded from the address in CR3.
>
> CR4.PKS is not in the list of CR4 bits that result in a PDPTE load.
> Since it has no effect on PAE paging, I would be surprised if it did
> result in a PDPTE load.

Oh, My mistake.

> >          if (kvm_valid_cr4(vcpu, cr4))
> >                  return 1;
> > @@ -1202,7 +1205,7 @@ static const u32 msrs_to_save_all[] = {
> >          MSR_IA32_RTIT_ADDR1_A, MSR_IA32_RTIT_ADDR1_B,
> >          MSR_IA32_RTIT_ADDR2_A, MSR_IA32_RTIT_ADDR2_B,
> >          MSR_IA32_RTIT_ADDR3_A, MSR_IA32_RTIT_ADDR3_B,
> > -       MSR_IA32_UMWAIT_CONTROL,
> > +       MSR_IA32_UMWAIT_CONTROL, MSR_IA32_PKRS,
>
> Should MSR_IA32_PKRS be added to the switch statement in
> kvm_init_msr_list()? Something like...
>
> case MSR_IA32_PKRS:
>          if (!kvm_cpu_cap_has(X86_FEATURE_PKRS))
>                  continue;
>          break;

Yes, this should be added.