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SubjectRe: [RFC PATCH v6 090/104] KVM: TDX: Handle TDX PV CPUID hypercall
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,

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

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