userfaultfd: provide pid in userfault msg

It could be useful for calculating downtime during postcopy live migration per vCPU. Side observer or application itself will be informed about proper task's sleep during userfaultfd processing. Process's thread id is being provided when user requeste it by setting UFFD_FEATURE_THREAD_ID bit into uffdio_api.features. Link: http://lkml.kernel.org/r/[email protected] Signed-off-by: Alexey Perevalov <[email protected]> Signed-off-by: Andrea Arcangeli <[email protected]> Cc: "Dr. David Alan Gilbert" <[email protected]> Cc: Maxime Coquelin <[email protected]> Cc: Mike Kravetz <[email protected]> Cc: Mike Rapoport <[email protected]> Signed-off-by: Andrew Morton <[email protected]> Signed-off-by: Linus Torvalds <[email protected]>
maraz · Sep 7, 2017 · 9d4ac93 · 9d4ac93
1 parent 2376dd7
commit 9d4ac93
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Showing 2 changed files with 13 additions and 5 deletions.
diff --git a/fs/userfaultfd.c b/fs/userfaultfd.c
@@ -178,7 +178,8 @@ static inline void msg_init(struct uffd_msg *msg)
 
 static inline struct uffd_msg userfault_msg(unsigned long address,
 					    unsigned int flags,
-					    unsigned long reason)
+					    unsigned long reason,
+					    unsigned int features)
 {
 	struct uffd_msg msg;
 	msg_init(&msg);
@@ -202,6 +203,8 @@ static inline struct uffd_msg userfault_msg(unsigned long address,
 		 * write protect fault.
 		 */
 		msg.arg.pagefault.flags |= UFFD_PAGEFAULT_FLAG_WP;
+	if (features & UFFD_FEATURE_THREAD_ID)
+		msg.arg.pagefault.ptid = task_pid_vnr(current);
 	return msg;
 }
 
@@ -422,7 +425,8 @@ int handle_userfault(struct vm_fault *vmf, unsigned long reason)
 
 	init_waitqueue_func_entry(&uwq.wq, userfaultfd_wake_function);
 	uwq.wq.private = current;
-	uwq.msg = userfault_msg(vmf->address, vmf->flags, reason);
+	uwq.msg = userfault_msg(vmf->address, vmf->flags, reason,
+			ctx->features);
 	uwq.ctx = ctx;
 	uwq.waken = false;
 

diff --git a/include/uapi/linux/userfaultfd.h b/include/uapi/linux/userfaultfd.h
@@ -24,7 +24,8 @@
 			   UFFD_FEATURE_EVENT_UNMAP |		\
 			   UFFD_FEATURE_MISSING_HUGETLBFS |	\
 			   UFFD_FEATURE_MISSING_SHMEM |		\
-			   UFFD_FEATURE_SIGBUS)
+			   UFFD_FEATURE_SIGBUS |		\
+			   UFFD_FEATURE_THREAD_ID)
 #define UFFD_API_IOCTLS				\
 	((__u64)1 << _UFFDIO_REGISTER |		\
 	 (__u64)1 << _UFFDIO_UNREGISTER |	\
@@ -79,6 +80,7 @@ struct uffd_msg {
 		struct {
 			__u64	flags;
 			__u64	address;
+			__u32   ptid;
 		} pagefault;
 
 		struct {
@@ -158,8 +160,9 @@ struct uffdio_api {
 	 * UFFD_FEATURE_SIGBUS feature means no page-fault
 	 * (UFFD_EVENT_PAGEFAULT) event will be delivered, instead
 	 * a SIGBUS signal will be sent to the faulting process.
-	 * The application process can enable this behavior by adding
-	 * it to uffdio_api.features.
+	 *
+	 * UFFD_FEATURE_THREAD_ID pid of the page faulted task_struct will
+	 * be returned, if feature is not requested 0 will be returned.
 	 */
 #define UFFD_FEATURE_PAGEFAULT_FLAG_WP		(1<<0)
 #define UFFD_FEATURE_EVENT_FORK			(1<<1)
@@ -169,6 +172,7 @@ struct uffdio_api {
 #define UFFD_FEATURE_MISSING_SHMEM		(1<<5)
 #define UFFD_FEATURE_EVENT_UNMAP		(1<<6)
 #define UFFD_FEATURE_SIGBUS			(1<<7)
+#define UFFD_FEATURE_THREAD_ID			(1<<8)
 	__u64 features;
 
 	__u64 ioctls;