mm/hmm: fix memremap.h, move dev_page_fault_t callback to hmm

The kbuild robot reported the following on a development branch that used
memremap.h in a new path:

   In file included from arch/m68k/include/asm/pgtable_mm.h:148:0,
                     from arch/m68k/include/asm/pgtable.h:5,
                     from include/linux/memremap.h:7,
                     from drivers//dax/bus.c:3:
    arch/m68k/include/asm/motorola_pgtable.h: In function 'pgd_offset':
 >> arch/m68k/include/asm/motorola_pgtable.h:199:11: error: dereferencing pointer to incomplete type 'const struct mm_struct'
      return mm->pgd + pgd_index(address);
               ^~

The ->page_fault() callback is specific to HMM.  Move it to 'struct
hmm_devmem' where the unusual asm/pgtable.h dependency can be contained in
include/linux/hmm.h.  Longer term refactoring this dependency out of HMM
is recommended, but in the meantime memremap.h remains generic.

Link: http://lkml.kernel.org/r/154534090899.3120190.6652620807617715272.stgit@dwillia2-desk3.amr.corp.intel.com
Fixes: 5042db43cc26 ("mm/ZONE_DEVICE: new type of ZONE_DEVICE memory...")
Signed-off-by: Dan Williams <dan.j.williams@intel.com>
Reviewed-by: "Jérôme Glisse" <jglisse@redhat.com>
Cc: Logan Gunthorpe <logang@deltatee.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

2 files changed, 24 insertions, 32 deletions

diff --git a/include/linux/hmm.h b/include/linux/hmm.h
index ed89fbc525d2..66f9ebbb1df3 100644
--- a/include/linux/hmm.h
+++ b/include/linux/hmm.h
@@ -69,6 +69,7 @@
 #define LINUX_HMM_H
 
 #include <linux/kconfig.h>
+#include <asm/pgtable.h>
 
 #if IS_ENABLED(CONFIG_HMM)
 
@@ -486,6 +487,7 @@ struct hmm_devmem_ops {
  * @device: device to bind resource to
  * @ops: memory operations callback
  * @ref: per CPU refcount
+ * @page_fault: callback when CPU fault on an unaddressable device page
  *
  * This an helper structure for device drivers that do not wish to implement
  * the gory details related to hotplugging new memoy and allocating struct
@@ -493,7 +495,28 @@ struct hmm_devmem_ops {
  *
  * Device drivers can directly use ZONE_DEVICE memory on their own if they
  * wish to do so.
+ *
+ * The page_fault() callback must migrate page back, from device memory to
+ * system memory, so that the CPU can access it. This might fail for various
+ * reasons (device issues,  device have been unplugged, ...). When such error
+ * conditions happen, the page_fault() callback must return VM_FAULT_SIGBUS and
+ * set the CPU page table entry to "poisoned".
+ *
+ * Note that because memory cgroup charges are transferred to the device memory,
+ * this should never fail due to memory restrictions. However, allocation
+ * of a regular system page might still fail because we are out of memory. If
+ * that happens, the page_fault() callback must return VM_FAULT_OOM.
+ *
+ * The page_fault() callback can also try to migrate back multiple pages in one
+ * chunk, as an optimization. It must, however, prioritize the faulting address
+ * over all the others.
  */
+typedef int (*dev_page_fault_t)(struct vm_area_struct *vma,
+				unsigned long addr,
+				const struct page *page,
+				unsigned int flags,
+				pmd_t *pmdp);
+
 struct hmm_devmem {
 	struct completion		completion;
 	unsigned long			pfn_first;
@@ -503,6 +526,7 @@ struct hmm_devmem {
 	struct dev_pagemap		pagemap;
 	const struct hmm_devmem_ops	*ops;
 	struct percpu_ref		ref;
+	dev_page_fault_t		page_fault;
 };
 
 /*
diff --git a/include/linux/memremap.h b/include/linux/memremap.h
index 55db66b3716f..f0628660d541 100644
--- a/include/linux/memremap.h
+++ b/include/linux/memremap.h
@@ -4,8 +4,6 @@
 #include <linux/ioport.h>
 #include <linux/percpu-refcount.h>
 
-#include <asm/pgtable.h>
-
 struct resource;
 struct device;
 
@@ -66,47 +64,18 @@ enum memory_type {
 };
 
 /*
- * For MEMORY_DEVICE_PRIVATE we use ZONE_DEVICE and extend it with two
- * callbacks:
- *   page_fault()
- *   page_free()
- *
  * Additional notes about MEMORY_DEVICE_PRIVATE may be found in
  * include/linux/hmm.h and Documentation/vm/hmm.rst. There is also a brief
  * explanation in include/linux/memory_hotplug.h.
  *
- * The page_fault() callback must migrate page back, from device memory to
- * system memory, so that the CPU can access it. This might fail for various
- * reasons (device issues,  device have been unplugged, ...). When such error
- * conditions happen, the page_fault() callback must return VM_FAULT_SIGBUS and
- * set the CPU page table entry to "poisoned".
- *
- * Note that because memory cgroup charges are transferred to the device memory,
- * this should never fail due to memory restrictions. However, allocation
- * of a regular system page might still fail because we are out of memory. If
- * that happens, the page_fault() callback must return VM_FAULT_OOM.
- *
- * The page_fault() callback can also try to migrate back multiple pages in one
- * chunk, as an optimization. It must, however, prioritize the faulting address
- * over all the others.
- *
- *
  * The page_free() callback is called once the page refcount reaches 1
  * (ZONE_DEVICE pages never reach 0 refcount unless there is a refcount bug.
  * This allows the device driver to implement its own memory management.)
- *
- * For MEMORY_DEVICE_PUBLIC only the page_free() callback matter.
  */
-typedef int (*dev_page_fault_t)(struct vm_area_struct *vma,
-				unsigned long addr,
-				const struct page *page,
-				unsigned int flags,
-				pmd_t *pmdp);
 typedef void (*dev_page_free_t)(struct page *page, void *data);
 
 /**
  * struct dev_pagemap - metadata for ZONE_DEVICE mappings
- * @page_fault: callback when CPU fault on an unaddressable device page
  * @page_free: free page callback when page refcount reaches 1
  * @altmap: pre-allocated/reserved memory for vmemmap allocations
  * @res: physical address range covered by @ref
@@ -117,7 +86,6 @@ typedef void (*dev_page_free_t)(struct page *page, void *data);
  * @type: memory type: see MEMORY_* in memory_hotplug.h
  */
 struct dev_pagemap {
-	dev_page_fault_t page_fault;
 	dev_page_free_t page_free;
 	struct vmem_altmap altmap;
 	bool altmap_valid;