Hi Peter,
Please see a few comments below.
Thanks,
Alex
On 3/22/21 11:08 PM, Peter Xu wrote:
Userfaultfd write-protect mode is supported starting from Linux 5.7.
Signed-off-by: Peter Xu <peterx@xxxxxxxxxx>
---
man2/ioctl_userfaultfd.2 | 84 ++++++++++++++++++++++++++++++++++++++--
1 file changed, 81 insertions(+), 3 deletions(-)
diff --git a/man2/ioctl_userfaultfd.2 b/man2/ioctl_userfaultfd.2
index d4a8375b8..5419687a6 100644
--- a/man2/ioctl_userfaultfd.2
+++ b/man2/ioctl_userfaultfd.2
@@ -234,6 +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)
@@ -322,9 +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
@@ -443,6 +445,16 @@ operation:
.TP
.B UFFDIO_COPY_MODE_DONTWAKE
Do not wake up the thread that waits for page-fault resolution
+.TP
+.B UFFDIO_COPY_MODE_WP
+Copy the page with read-only permission.
+This allows the user to trap the next write to the page,
+which will block and generate another write-protect userfault message.
s/write-protect/write-protected/
?
+This is only used when both
+.B UFFDIO_REGISTER_MODE_MISSING
+and
+.B UFFDIO_REGISTER_MODE_WP
+modes are enabled for the registered range.
.PP
The
.I copy
@@ -654,6 +666,72 @@ 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)
+Write-protect or write-unprotect an userfaultfd registered memory range
+registered 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 mode bits 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,
+which can be used to resolve an userfaultfd write-protect page fault.
+.TP
+.B UFFDIO_WRITEPROTECT_MODE_DONTWAKE
+When this mode bit is set,
+do not wake up any thread that waits for page-fault resolution after the operation.
+This could only be specified if
+.B UFFDIO_WRITEPROTECT_MODE_WP
+is not specified.
+.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.
Maybe: "The process was interrupted; retry this call."?
I don't know what other pager say about this kind of error.
+.TP
+.B ENOENT
+The range specified in
+.I range
+is not valid.
I'm not sure how this is different from the wording above in EINVAL. An
"otherwise invalid range" was already giving EINVAL?
+For example, the virtual address does not exist,
+or not registered with userfaultfd write-protect mode.
+.TP
+.B EFAULT
+Encountered a generic fault during processing.
What is a "generic fault"?
.SH RETURN VALUE
See descriptions of the individual operations, above.
.SH ERRORS
--
Alejandro Colomar
Linux man-pages comaintainer; https://www.kernel.org/doc/man-pages/
http://www.alejandro-colomar.es/
