KVM: x86: Add a VALID_MASK for the flags in kvm_msr_filter_range

Add the mask KVM_MSR_FILTER_RANGE_VALID_MASK for the flags in the
struct kvm_msr_filter_range.  This simplifies checks that validate
these flags, and makes it easier to introduce new flags in the future.

No functional change intended.

Signed-off-by: Aaron Lewis <aaronlewis@google.com>
Message-Id: <20220921151525.904162-5-aaronlewis@google.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

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

@@ -214,6 +214,8 @@ struct kvm_msr_list {
 struct kvm_msr_filter_range {
 #define KVM_MSR_FILTER_READ  (1 << 0)
 #define KVM_MSR_FILTER_WRITE (1 << 1)
+#define KVM_MSR_FILTER_RANGE_VALID_MASK (KVM_MSR_FILTER_READ | \
+					 KVM_MSR_FILTER_WRITE)
 	__u32 flags;
 	__u32 nmsrs; /* number of msrs in bitmap */
 	__u32 base;  /* MSR index the bitmap starts at */

arch/x86/kvm/x86.c

@@ -6407,7 +6407,7 @@ static int kvm_add_msr_filter(struct kvm_x86_msr_filter *msr_filter,
 	if (!user_range->nmsrs)
 		return 0;
 
-	if (user_range->flags & ~(KVM_MSR_FILTER_READ | KVM_MSR_FILTER_WRITE))
+	if (user_range->flags & ~KVM_MSR_FILTER_RANGE_VALID_MASK)
 		return -EINVAL;
 
 	if (!user_range->flags)