iommu/ioasid: Introduce a helper to check for valid PASIDs

Define a pasid_valid() helper to check if a given PASID is valid.

  [ bp: Massage commit message. ]
Suggested-by: Ashok Raj <ashok.raj@intel.com>
Suggested-by: Jacob Pan <jacob.jun.pan@linux.intel.com>
Signed-off-by: Fenghua Yu <fenghua.yu@intel.com>
Signed-off-by: Borislav Petkov <bp@suse.de>
Reviewed-by: Tony Luck <tony.luck@intel.com>
Reviewed-by: Thomas Gleixner <tglx@linutronix.de>
Reviewed-by: Lu Baolu <baolu.lu@linux.intel.com>
Link: https://lore.kernel.org/r/20220207230254.3342514-4-fenghua.yu@intel.com

include/linux/ioasid.h

@@ -41,6 +41,10 @@ void *ioasid_find(struct ioasid_set *set, ioasid_t ioasid,
 int ioasid_register_allocator(struct ioasid_allocator_ops *allocator);
 void ioasid_unregister_allocator(struct ioasid_allocator_ops *allocator);
 int ioasid_set_data(ioasid_t ioasid, void *data);
+static inline bool pasid_valid(ioasid_t ioasid)
+{
+	return ioasid != INVALID_IOASID;
+}
 
 #else /* !CONFIG_IOASID */
 static inline ioasid_t ioasid_alloc(struct ioasid_set *set, ioasid_t min,
@@ -78,5 +82,10 @@ static inline int ioasid_set_data(ioasid_t ioasid, void *data)
 	return -ENOTSUPP;
 }
 
+static inline bool pasid_valid(ioasid_t ioasid)
+{
+	return false;
+}
+
 #endif /* CONFIG_IOASID */
 #endif /* __LINUX_IOASID_H */