KVM: x86: Add infrastructure for MSR filtering

In the following commits we will add pieces of MSR filtering.
To ensure that code compiles even with the feature half-merged, let's add
a few stubs and struct definitions before the real patches start.
Signed-off-by: Alexander Graf <graf@amazon.com>

Message-Id: <20200925143422.21718-4-graf@amazon.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

arch/x86/include/asm/kvm_host.h

@@ -1235,6 +1235,7 @@ struct kvm_x86_ops {
 	int (*enable_direct_tlbflush)(struct kvm_vcpu *vcpu);
 
 	void (*migrate_timers)(struct kvm_vcpu *vcpu);
+	void (*msr_filter_changed)(struct kvm_vcpu *vcpu);
 };
 
 struct kvm_x86_nested_ops {

arch/x86/include/uapi/asm/kvm.h

@@ -192,6 +192,8 @@ struct kvm_msr_list {
 	__u32 indices[0];
 };
 
+#define KVM_MSR_FILTER_READ  (1 << 0)
+#define KVM_MSR_FILTER_WRITE (1 << 1)
 
 struct kvm_cpuid_entry {
 	__u32 function;

arch/x86/kvm/x86.c

@@ -1488,6 +1488,12 @@ void kvm_enable_efer_bits(u64 mask)
 }
 EXPORT_SYMBOL_GPL(kvm_enable_efer_bits);
 
+bool kvm_msr_allowed(struct kvm_vcpu *vcpu, u32 index, u32 type)
+{
+	return true;
+}
+EXPORT_SYMBOL_GPL(kvm_msr_allowed);
+
 /*
  * Write @data into the MSR specified by @index.  Select MSR specific fault
  * checks are bypassed if @host_initiated is %true.

arch/x86/kvm/x86.h

@@ -374,6 +374,7 @@ bool kvm_vcpu_exit_request(struct kvm_vcpu *vcpu);
 int kvm_handle_memory_failure(struct kvm_vcpu *vcpu, int r,
 			      struct x86_exception *e);
 int kvm_handle_invpcid(struct kvm_vcpu *vcpu, unsigned long type, gva_t gva);
+bool kvm_msr_allowed(struct kvm_vcpu *vcpu, u32 index, u32 type);
 
 #define  KVM_MSR_RET_INVALID  2