mm: add FAULT_FLAG_VMA_LOCK flag

Add a new flag to distinguish page faults handled under protection of
per-vma lock.

[[e-mail]: document FAULT_FLAG_VMA_LOCK flag]
Link: https://lkml.kernel.org/r/[e-mail]
Link: https://lore.kernel.org/all/[e-mail]/
Link: https://lkml.kernel.org/r/[e-mail]
Signed-off-by: Suren Baghdasaryan <[e-mail]>
Reviewed-by: Laurent Dufour <[e-mail]>
Cc: Dan Carpenter <[e-mail]>
Cc: David Hildenbrand <[e-mail]>
Cc: David Howells <[e-mail]>
Cc: Hugh Dickins <[e-mail]>
Cc: Jason Gunthorpe <[e-mail]>
Cc: Liam R. Howlett <[e-mail]>
Cc: Mathieu Desnoyers <[e-mail]>
Cc: Matthew Wilcox <[e-mail]>
Cc: Pavel Tatashin <[e-mail]>
Cc: Yu Zhao <[e-mail]>
Signed-off-by: Andrew Morton <[e-mail]>

include/linux/mm.h

···
 	{ FAULT_FLAG_USER,		"USER" }, \
 	{ FAULT_FLAG_REMOTE,		"REMOTE" }, \
 	{ FAULT_FLAG_INSTRUCTION,	"INSTRUCTION" }, \
-	{ FAULT_FLAG_INTERRUPTIBLE,	"INTERRUPTIBLE" }
+	{ FAULT_FLAG_INTERRUPTIBLE,	"INTERRUPTIBLE" }, \
+	{ FAULT_FLAG_VMA_LOCK,		"VMA_LOCK" }
 
 /*
  * vm_fault is filled by the pagefault handler and passed to the vma's

include/linux/mm_types.h

···
  *                      mapped after the fault.
  * @FAULT_FLAG_ORIG_PTE_VALID: whether the fault has vmf->orig_pte cached.
  *                        We should only access orig_pte if this flag set.
+ * @FAULT_FLAG_VMA_LOCK: The fault is handled under VMA lock.
  *
  * About @FAULT_FLAG_ALLOW_RETRY and @FAULT_FLAG_TRIED: we can specify
  * whether we would allow page faults to retry by specifying these two
···
 	FAULT_FLAG_INTERRUPTIBLE =	1 << 9,
 	FAULT_FLAG_UNSHARE =		1 << 10,
 	FAULT_FLAG_ORIG_PTE_VALID =	1 << 11,
+	FAULT_FLAG_VMA_LOCK =		1 << 12,
 };
 
 typedef unsigned int __bitwise zap_flags_t;