mm/hmm: define the pre-processor related parts of hmm.h even if disabled

Only the function calls are stubbed out with static inlines that always
fail. This is the standard way to write a header for an optional component
and makes it easier for drivers that only optionally need HMM_MIRROR.

Link: https://lore.kernel.org/r/20191112202231.3856-5-jgg@ziepe.ca
Reviewed-by: Jérôme Glisse <jglisse@redhat.com>
Tested-by: Ralph Campbell <rcampbell@nvidia.com>
Reviewed-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Jason Gunthorpe <jgg@mellanox.com>

include/linux/hmm.h

@@ -62,8 +62,6 @@
 #include <linux/kconfig.h>
 #include <asm/pgtable.h>
 
-#ifdef CONFIG_HMM_MIRROR
-
 #include <linux/device.h>
 #include <linux/migrate.h>
 #include <linux/memremap.h>
@@ -374,6 +372,15 @@ struct hmm_mirror {
 	struct list_head		list;
 };
 
+/*
+ * Retry fault if non-blocking, drop mmap_sem and return -EAGAIN in that case.
+ */
+#define HMM_FAULT_ALLOW_RETRY		(1 << 0)
+
+/* Don't fault in missing PTEs, just snapshot the current state. */
+#define HMM_FAULT_SNAPSHOT		(1 << 1)
+
+#ifdef CONFIG_HMM_MIRROR
 int hmm_mirror_register(struct hmm_mirror *mirror, struct mm_struct *mm);
 void hmm_mirror_unregister(struct hmm_mirror *mirror);
 
@@ -383,14 +390,6 @@ void hmm_mirror_unregister(struct hmm_mirror *mirror);
 int hmm_range_register(struct hmm_range *range, struct hmm_mirror *mirror);
 void hmm_range_unregister(struct hmm_range *range);
 
-/*
- * Retry fault if non-blocking, drop mmap_sem and return -EAGAIN in that case.
- */
-#define HMM_FAULT_ALLOW_RETRY		(1 << 0)
-
-/* Don't fault in missing PTEs, just snapshot the current state. */
-#define HMM_FAULT_SNAPSHOT		(1 << 1)
-
 long hmm_range_fault(struct hmm_range *range, unsigned int flags);
 
 long hmm_range_dma_map(struct hmm_range *range,
@@ -401,6 +400,44 @@ long hmm_range_dma_unmap(struct hmm_range *range,
 			 struct device *device,
 			 dma_addr_t *daddrs,
 			 bool dirty);
+#else
+int hmm_mirror_register(struct hmm_mirror *mirror, struct mm_struct *mm)
+{
+	return -EOPNOTSUPP;
+}
+
+void hmm_mirror_unregister(struct hmm_mirror *mirror)
+{
+}
+
+int hmm_range_register(struct hmm_range *range, struct hmm_mirror *mirror)
+{
+	return -EOPNOTSUPP;
+}
+
+void hmm_range_unregister(struct hmm_range *range)
+{
+}
+
+static inline long hmm_range_fault(struct hmm_range *range, unsigned int flags)
+{
+	return -EOPNOTSUPP;
+}
+
+static inline long hmm_range_dma_map(struct hmm_range *range,
+				     struct device *device, dma_addr_t *daddrs,
+				     unsigned int flags)
+{
+	return -EOPNOTSUPP;
+}
+
+static inline long hmm_range_dma_unmap(struct hmm_range *range,
+				       struct device *device,
+				       dma_addr_t *daddrs, bool dirty)
+{
+	return -EOPNOTSUPP;
+}
+#endif
 
 /*
  * HMM_RANGE_DEFAULT_TIMEOUT - default timeout (ms) when waiting for a range
@@ -411,6 +448,4 @@ long hmm_range_dma_unmap(struct hmm_range *range,
  */
 #define HMM_RANGE_DEFAULT_TIMEOUT 1000
 
-#endif /* IS_ENABLED(CONFIG_HMM_MIRROR) */
-
 #endif /* LINUX_HMM_H */

kernel/fork.c

@@ -40,7 +40,6 @@
 #include <linux/binfmts.h>
 #include <linux/mman.h>
 #include <linux/mmu_notifier.h>
-#include <linux/hmm.h>
 #include <linux/fs.h>
 #include <linux/mm.h>
 #include <linux/vmacache.h>