[PATCH 4/4] ioctl_userfaultfd.2: Add write-protect mode docs

Peter Xu
2021-03-04T02:02:55Z

Userfaultfd write-protect mode is supported starting from Linux 5.7.

Signed-off-by: Peter Xu <peterx@redhat.com>
---
man2/ioctl_userfaultfd.2 | 74 +++++++++++++++++++++++++++++++++++++---
1 file changed, 70 insertions(+), 4 deletions(-)

diff --git a/man2/ioctl_userfaultfd.2 b/man2/ioctl_userfaultfd.2
index 1965d1932..3feb888a8 100644
--- a/man2/ioctl_userfaultfd.2
+++ b/man2/ioctl_userfaultfd.2
@@ -208,10 +208,11 @@ signal will be sent to the faulting process.
Applications using this
feature will not require the use of a userfaultfd monitor for processing
memory accesses to the regions registered with userfaultfd.
+.TP
.BR UFFD_FEATURE_THREAD_ID " (since Linux 4.14)"
If this feature bit is set,
.I uffd_msg.pagefault.feat.ptid
-Will be set
+will be set to the faulted thread ID for each page fault message.
.PP
The returned
.I ioctls
@@ -233,6 +234,11 @@ operation is supported.
The
.B UFFDIO_UNREGISTER
operation is supported.
+.TP
+.B 1 << _UFFDIO_WRITEPROTECT
+The
+.B UFFDIO_WRITEPROTECT
+operation is supported.
.PP
This
.BR ioctl (2)
@@ -321,9 +327,6 @@ Track page faults on missing pages.
.B UFFDIO_REGISTER_MODE_WP
Track page faults on write-protected pages.
.PP
-Currently, the only supported mode is
-.BR UFFDIO_REGISTER_MODE_MISSING .
-.PP
If the operation is successful, the kernel modifies the
.I ioctls
bit-mask field to indicate which
@@ -653,6 +656,69 @@ field of the
structure was not a multiple of the system page size; or
.I len
was zero; or the specified range was otherwise invalid.
+.SS UFFDIO_WRITEPROTECT
+(Since Linux 5.7) Do write-protect or write-unprotect for an userfaultfd
+registered memory range with mode
+.BR UFFDIO_REGISTER_MODE_WP .
+.PP
+The
+.I argp
+argument is a pointer to a
+.I uffdio_range
+structure as shown below:
+.PP
+.in +4n
+.EX
+struct uffdio_writeprotect {
+ struct uffdio_range range; /* Range to change write permission */
+ __u64 mode; /* Mode to change write permission */
+};
+.EE
+.in
+There're two modes that are supported in this structure:
+.TP
+.B UFFDIO_WRITEPROTECT_MODE_WP
+When this mode bit is set, the ioctl will be a write-protect operation upon the
+memory range specified by
+.IR range .
+Otherwise it'll be a write-unprotect operation upon the specified range.
+.TP
+.B UFFDIO_WRITEPROTECT_MODE_DONTWAKE
+Do not wake up the thread that waits for page-fault resolution after the
+operation. This could only be specified if
+.B UFFDIO_WRITEPROTECT_MODE_WP
+is not specified (in a resolving stage, not protecting stage).
+.PP
+This
+.BR ioctl (2)
+operation returns 0 on success.
+On error, \-1 is returned and
+.I errno
+is set to indicate the error.
+Possible errors include:
+.TP
+.B EINVAL
+The
+.I start
+or the
+.I len
+field of the
+.I ufdio_range
+structure was not a multiple of the system page size; or
+.I len
+was zero; or the specified range was otherwise invalid.
+.TP
+.B EAGAIN
+The process was interrupted and need to retry.
+.TP
+.B ENOENT
+The range specified in
+.I range
+is not valid. E.g., the virtual address does not exist, or not registered with
+userfaultfd write-protect mode.
+.TP
+.B EFAULT
+Encountered a generic fault during processing.
.SH RETURN VALUE
See descriptions of the individual operations, above.
.SH ERRORS
--
2.26.2