Re: [PATCH v19 105/130] KVM: TDX: handle KVM hypercall with TDG.VP.VMCALL

Isaku Yamahata
2024-04-04T01:27:27Z

On Tue, Apr 02, 2024 at 04:52:46PM +0800,
Chao Gao <chao.gao@intel.com> wrote:

> >+static int tdx_emulate_vmcall(struct kvm_vcpu *vcpu)
> >+{
> >+ unsigned long nr, a0, a1, a2, a3, ret;
> >+
>
> do you need to emulate xen/hyper-v hypercalls here?

No. kvm_emulate_hypercall() handles xen/hyper-v hypercalls,
__kvm_emulate_hypercall() doesn't.

> Nothing tells userspace that xen/hyper-v hypercalls are not supported and
> so userspace may expose related CPUID leafs to TD guests.
>
> >+ /*
> >+ * ABI for KVM tdvmcall argument:
> >+ * In Guest-Hypervisor Communication Interface(GHCI) specification,
> >+ * Non-zero leaf number (R10 != 0) is defined to indicate
> >+ * vendor-specific. KVM uses this for KVM hypercall. NOTE: KVM
> >+ * hypercall number starts from one. Zero isn't used for KVM hypercall
> >+ * number.
> >+ *
> >+ * R10: KVM hypercall number
> >+ * arguments: R11, R12, R13, R14.
> >+ */
> >+ nr = kvm_r10_read(vcpu);
> >+ a0 = kvm_r11_read(vcpu);
> >+ a1 = kvm_r12_read(vcpu);
> >+ a2 = kvm_r13_read(vcpu);
> >+ a3 = kvm_r14_read(vcpu);
> >+
> >+ ret = __kvm_emulate_hypercall(vcpu, nr, a0, a1, a2, a3, true, 0);
> >+
> >+ tdvmcall_set_return_code(vcpu, ret);
> >+
> >+ if (nr == KVM_HC_MAP_GPA_RANGE && !ret)
> >+ return 0;
>
> Can you add a comment to call out that KVM_HC_MAP_GPA_RANGE is redirected to
> the userspace?

Yes, this is confusing. We should refactor kvm_emulate_hypercall() more so that
the caller shouldn't care about the return value like this. Will refactor it
and update this patch.
--
Isaku Yamahata <isaku.yamahata@intel.com>