KVM: TDX: Handle TDX PV port I/O hypercall

Emulate port I/O requested by TDX guest via TDVMCALL with leaf
Instruction.IO (same value as EXIT_REASON_IO_INSTRUCTION) according to
TDX Guest Host Communication Interface (GHCI).

All port I/O instructions inside the TDX guest trigger the #VE exception.
On #VE triggered by I/O instructions, TDX guest can call TDVMCALL with
leaf Instruction.IO to request VMM to emulate I/O instructions.

Similar to normal port I/O emulation, try to handle the port I/O in kernel
first, if kernel can't support it, forward the request to userspace.

Note string I/O operations are not supported in TDX.  Guest should unroll
them before calling the TDVMCALL.

Suggested-by: Sean Christopherson <seanjc@google.com>
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>
Reviewed-by: Paolo Bonzini <pbonzini@redhat.com>
Message-ID: <20250222014225.897298-9-binbin.wu@linux.intel.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

Author: yamahata

arch/x86/kvm/vmx/tdx.c

@@ -808,6 +808,8 @@ int tdx_vcpu_pre_run(struct kvm_vcpu *vcpu)
 static __always_inline u32 tdcall_to_vmx_exit_reason(struct kvm_vcpu *vcpu)
 {
 	switch (tdvmcall_leaf(vcpu)) {
+	case EXIT_REASON_IO_INSTRUCTION:
+		return tdvmcall_leaf(vcpu);
 	default:
 		break;
 	}
@@ -1130,6 +1132,64 @@ static int tdx_report_fatal_error(struct kvm_vcpu *vcpu)
 	return 0;
 }
 
+static int tdx_complete_pio_out(struct kvm_vcpu *vcpu)
+{
+	vcpu->arch.pio.count = 0;
+	return 1;
+}
+
+static int tdx_complete_pio_in(struct kvm_vcpu *vcpu)
+{
+	struct x86_emulate_ctxt *ctxt = vcpu->arch.emulate_ctxt;
+	unsigned long val = 0;
+	int ret;
+
+	ret = ctxt->ops->pio_in_emulated(ctxt, vcpu->arch.pio.size,
+					 vcpu->arch.pio.port, &val, 1);
+
+	WARN_ON_ONCE(!ret);
+
+	tdvmcall_set_return_val(vcpu, val);
+
+	return 1;
+}
+
+static int tdx_emulate_io(struct kvm_vcpu *vcpu)
+{
+	struct vcpu_tdx *tdx = to_tdx(vcpu);
+	struct x86_emulate_ctxt *ctxt = vcpu->arch.emulate_ctxt;
+	unsigned long val = 0;
+	unsigned int port;
+	u64 size, write;
+	int ret;
+
+	++vcpu->stat.io_exits;
+
+	size = tdx->vp_enter_args.r12;
+	write = tdx->vp_enter_args.r13;
+	port = tdx->vp_enter_args.r14;
+
+	if ((write != 0 && write != 1) || (size != 1 && size != 2 && size != 4)) {
+		tdvmcall_set_return_code(vcpu, TDVMCALL_STATUS_INVALID_OPERAND);
+		return 1;
+	}
+
+	if (write) {
+		val = tdx->vp_enter_args.r15;
+		ret = ctxt->ops->pio_out_emulated(ctxt, size, port, &val, 1);
+	} else {
+		ret = ctxt->ops->pio_in_emulated(ctxt, size, port, &val, 1);
+	}
+
+	if (!ret)
+		vcpu->arch.complete_userspace_io = write ? tdx_complete_pio_out :
+							   tdx_complete_pio_in;
+	else if (!write)
+		tdvmcall_set_return_val(vcpu, val);
+
+	return ret;
+}
+
 static int handle_tdvmcall(struct kvm_vcpu *vcpu)
 {
 	switch (tdvmcall_leaf(vcpu)) {
@@ -1507,6 +1567,8 @@ int tdx_handle_exit(struct kvm_vcpu *vcpu, fastpath_t fastpath)
 		return handle_tdvmcall(vcpu);
 	case EXIT_REASON_VMCALL:
 		return tdx_emulate_vmcall(vcpu);
+	case EXIT_REASON_IO_INSTRUCTION:
+		return tdx_emulate_io(vcpu);
 	default:
 		break;
 	}