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/20170802165145.22628-6-aarcange@redhat.com
Signed-off-by: Alexey Perevalov <a.perevalov@samsung.com>
Signed-off-by: Andrea Arcangeli <aarcange@redhat.com>
Cc: "Dr. David Alan Gilbert" <dgilbert@redhat.com>
Cc: Maxime Coquelin <maxime.coquelin@redhat.com>
Cc: Mike Kravetz <mike.kravetz@oracle.com>
Cc: Mike Rapoport <rppt@linux.vnet.ibm.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

diff --git a/fs/userfaultfd.c b/fs/userfaultfd.c
index 5fd4d846691f0f0a503a71ed7a74399efe93ce6d..665bf7a930b26b5d40448f9b7ed92eea1ac7519f 100644 (file)
--- 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
index d39d5db567714493727de929d7c992e222d0214c..2b24c28d99a734119796977a6569fcdf0577de92 100644 (file)
--- 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;