[PATCH 3/7] KVM: TDX: Handle KVM hypercall with TDG.VP.VMCALL

[Binbin Wu <binbin.wu@linux.intel.com>]

From: Isaku Yamahata <isaku.yamahata@intel.com>

Handle KVM hypercall for TDX according to TDX Guest-Host Communication
Interface (GHCI) specification.

The TDX GHCI specification defines the ABI for the guest TD to issue
hypercalls.   When R10 is non-zero, it indicates the TDG.VP.VMCALL is
vendor-specific.  KVM uses R10 as KVM hypercall number and R11-R14
as 4 arguments, while the error code is returned in R10.  Follow the
ABI and handle the KVM hypercall for TDX.

Signed-off-by: Isaku Yamahata <isaku.yamahata@intel.com>
Co-developed-by: Binbin Wu <binbin.wu@linux.intel.com>
Signed-off-by: Binbin Wu <binbin.wu@linux.intel.com>
---
Hypercalls exit to userspace breakout:
- Renamed from "KVM: TDX: handle KVM hypercall with TDG.VP.VMCALL" to
  "KVM: TDX: Handle KVM hypercall with TDG.VP.VMCALL".
- Update the change log.
- Rebased on Sean's "Prep KVM hypercall handling for TDX" patch set.
  https://lore.kernel.org/kvm/20241128004344.4072099-1-seanjc@google.com
- Use the right register (i.e. R10) to set the return code after returning
  back from userspace.
---
 arch/x86/kvm/vmx/tdx.c | 31 +++++++++++++++++++++++++++++++
 1 file changed, 31 insertions(+)

diff --git a/arch/x86/kvm/vmx/tdx.c b/arch/x86/kvm/vmx/tdx.c
index 19fd8a5dabd0..4cc55b120ab0 100644
--- a/arch/x86/kvm/vmx/tdx.c
+++ b/arch/x86/kvm/vmx/tdx.c
@@ -957,8 +957,39 @@ static int tdx_handle_triple_fault(struct kvm_vcpu *vcpu)
 	return 0;
 }
 
+
+static int complete_hypercall_exit(struct kvm_vcpu *vcpu)
+{
+	kvm_r10_write(vcpu, vcpu->run->hypercall.ret);
+	return 1;
+}
+
+static int tdx_emulate_vmcall(struct kvm_vcpu *vcpu)
+{
+	int r;
+
+	/*
+	 * 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.
+	 */
+	r = __kvm_emulate_hypercall(vcpu, r10, r11, r12, r13, r14, true, 0,
+				    complete_hypercall_exit);
+
+	return r > 0;
+}
+
 static int handle_tdvmcall(struct kvm_vcpu *vcpu)
 {
+	if (tdvmcall_exit_type(vcpu))
+		return tdx_emulate_vmcall(vcpu);
+
 	switch (tdvmcall_leaf(vcpu)) {
 	default:
 		break;
-- 
2.46.0