KVM: x86: Use static_call() for copy/move encryption context ioctls()

Define and use static_call()s for .vm_{copy,move}_enc_context_from(),
mostly so that the op is defined in kvm-x86-ops.h.  This will allow using
KVM_X86_OP in vendor code to wire up the implementation.  Any performance
gains eeked out by using static_call() is a happy bonus and not the
primary motiviation.

Opportunistically refactor the code to reduce indentation and keep line
lengths reasonable, and to be consistent when wrapping versus running
a bit over the 80 char soft limit.
Signed-off-by: Sean Christopherson <seanjc@google.com>
Message-Id: <20220128005208.4008533-12-seanjc@google.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

arch/x86/include/asm/kvm-x86-ops.h

@@ -115,6 +115,8 @@ KVM_X86_OP(enable_smi_window)
 KVM_X86_OP_NULL(mem_enc_op)
 KVM_X86_OP_NULL(mem_enc_reg_region)
 KVM_X86_OP_NULL(mem_enc_unreg_region)
+KVM_X86_OP_NULL(vm_copy_enc_context_from)
+KVM_X86_OP_NULL(vm_move_enc_context_from)
 KVM_X86_OP(get_msr_feature)
 KVM_X86_OP(can_emulate_instruction)
 KVM_X86_OP(apic_init_signal_blocked)

arch/x86/kvm/x86.c

@@ -5975,15 +5975,18 @@ int kvm_vm_ioctl_enable_cap(struct kvm *kvm,
 #endif
 	case KVM_CAP_VM_COPY_ENC_CONTEXT_FROM:
 		r = -EINVAL;
-		if (kvm_x86_ops.vm_copy_enc_context_from)
-			r = kvm_x86_ops.vm_copy_enc_context_from(kvm, cap->args[0]);
-		return r;
+		if (!kvm_x86_ops.vm_copy_enc_context_from)
+			break;
+
+		r = static_call(kvm_x86_vm_copy_enc_context_from)(kvm, cap->args[0]);
+		break;
 	case KVM_CAP_VM_MOVE_ENC_CONTEXT_FROM:
 		r = -EINVAL;
-		if (kvm_x86_ops.vm_move_enc_context_from)
-			r = kvm_x86_ops.vm_move_enc_context_from(
-				kvm, cap->args[0]);
-		return r;
+		if (!kvm_x86_ops.vm_move_enc_context_from)
+			break;
+
+		r = static_call(kvm_x86_vm_move_enc_context_from)(kvm, cap->args[0]);
+		break;
 	case KVM_CAP_EXIT_HYPERCALL:
 		if (cap->args[0] & ~KVM_EXIT_HYPERCALL_VALID_MASK) {
 			r = -EINVAL;