diff mbox series

[v5,1/4] userfaultfd.2: Add UFFD_FEATURE_THREAD_ID docs

Message ID 20210329221833.517923-2-peterx@redhat.com (mailing list archive)
State New, archived
Headers show
Series man2: udpate mm/userfaultfd manpages to latest | expand

Commit Message

Peter Xu March 29, 2021, 10:18 p.m. UTC 
UFFD_FEATURE_THREAD_ID is supported since Linux 4.14.

Acked-by: Mike Rapoport <rppt@linux.vnet.ibm.com>
Signed-off-by: Peter Xu <peterx@redhat.com>
---
 man2/userfaultfd.2 | 13 +++++++++++++
 1 file changed, 13 insertions(+)
diff mbox series

Patch

diff --git a/man2/userfaultfd.2 b/man2/userfaultfd.2
index e7dc9f813..5c41e4816 100644
--- a/man2/userfaultfd.2
+++ b/man2/userfaultfd.2
@@ -77,6 +77,13 @@  When the last file descriptor referring to a userfaultfd object is closed,
 all memory ranges that were registered with the object are unregistered
 and unread events are flushed.
 .\"
+.PP
+Since Linux 4.14, userfaultfd page fault message can selectively embed faulting
+thread ID information into the fault message.
+One needs to enable this feature explicitly using the
+.BR UFFD_FEATURE_THREAD_ID
+feature bit when initializing the userfaultfd context.
+By default, thread ID reporting is disabled.
 .SS Usage
 The userfaultfd mechanism is designed to allow a thread in a multithreaded
 program to perform user-space paging for the other threads in the process.
@@ -229,6 +236,9 @@  struct uffd_msg {
         struct {
             __u64 flags;    /* Flags describing fault */
             __u64 address;  /* Faulting address */
+            union {
+                __u32 ptid; /* Thread ID of the fault */
+            } feat;
         } pagefault;
 
         struct {            /* Since Linux 4.11 */
@@ -358,6 +368,9 @@  otherwise it is a read fault.
 .\" UFFD_PAGEFAULT_FLAG_WP is not yet supported.
 .RE
 .TP
+.I pagefault.feat.pid
+The thread ID that triggered the page fault.
+.TP
 .I fork.ufd
 The file descriptor associated with the userfault object
 created for the child created by