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    SubjectRe: [RFC PATCH v6 090/104] KVM: TDX: Handle TDX PV CPUID hypercall
    On Wed, Jun 29, 2022 at 3:14 AM Isaku Yamahata <isaku.yamahata@gmail.com> wrote:
    >
    > On Tue, Jun 14, 2022 at 11:15:00AM -0700,
    > Sagi Shahar <sagis@google.com> wrote:
    >
    > > On Thu, May 5, 2022 at 11:16 AM <isaku.yamahata@intel.com> wrote:
    > > >
    > > > From: Isaku Yamahata <isaku.yamahata@intel.com>
    > > >
    > > > Wire up TDX PV CPUID hypercall to the KVM backend function.
    > > >
    > > > Signed-off-by: Isaku Yamahata <isaku.yamahata@intel.com>
    > > > ---
    > > > arch/x86/kvm/vmx/tdx.c | 22 ++++++++++++++++++++++
    > > > 1 file changed, 22 insertions(+)
    > > >
    > > > diff --git a/arch/x86/kvm/vmx/tdx.c b/arch/x86/kvm/vmx/tdx.c
    > > > index 9c712f661a7c..c7cdfee397ec 100644
    > > > --- a/arch/x86/kvm/vmx/tdx.c
    > > > +++ b/arch/x86/kvm/vmx/tdx.c
    > > > @@ -946,12 +946,34 @@ static int tdx_emulate_vmcall(struct kvm_vcpu *vcpu)
    > > > return 1;
    > > > }
    > > >
    > > > +static int tdx_emulate_cpuid(struct kvm_vcpu *vcpu)
    > > > +{
    > > > + u32 eax, ebx, ecx, edx;
    > > > +
    > > > + /* EAX and ECX for cpuid is stored in R12 and R13. */
    > > > + eax = tdvmcall_a0_read(vcpu);
    > > > + ecx = tdvmcall_a1_read(vcpu);
    > > > +
    > > > + kvm_cpuid(vcpu, &eax, &ebx, &ecx, &edx, true);
    > >
    > > According to the GHCI spec section 3.6
    > > (TDG.VP.VMCALL<Instruction.CPUID>) we should return
    > > VMCALL_INVALID_OPERAND if an invalid CPUID is requested.
    > >
    > > kvm_cpuid already returns false in this case so we should use that
    > > return value to set the tdvmcall return code in case of invalid leaf.
    >
    > Based on CPUID instruction, cpuid results in #UD when lock prefix is used or
    > earlier CPU that doesn't support cpuid instruction.
    > So I'm not sure what CPUID input result in INVALID_OPERAND error.
    > Does the following make sense for you?
    >
    > --- a/arch/x86/kvm/vmx/tdx.c
    > +++ b/arch/x86/kvm/vmx/tdx.c
    > @@ -1347,7 +1347,7 @@ static int tdx_emulate_cpuid(struct kvm_vcpu *vcpu)
    > eax = tdvmcall_a0_read(vcpu);
    > ecx = tdvmcall_a1_read(vcpu);
    >
    > - kvm_cpuid(vcpu, &eax, &ebx, &ecx, &edx, true);
    > + kvm_cpuid(vcpu, &eax, &ebx, &ecx, &edx, false);
    >
    > tdvmcall_a0_write(vcpu, eax);
    > tdvmcall_a1_write(vcpu, ebx);
    >
    > thanks,

    If any CPUID request is considered valid, then perhaps the spec itself
    needs to be updated.

    Right now it clearly states that TDG.VP.VMCALL_INVALID_OPERAND is
    returned if "Invalid CPUID requested" which I understood as a
    non-existing leaf. But if you say that a non-existing leaf is still a
    valid CPUID request than I'm not sure what "Invalid CPUID requested"
    means in the spec itself.

    >
    > --
    > Isaku Yamahata <isaku.yamahata@gmail.com>

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