Hi Peter,
A few more comments below.
Thanks,
Alex
On 3/10/21 11:23 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 | 81 ++++++++++++++++++++++++++++++++++++++--
> 1 file changed, 78 insertions(+), 3 deletions(-)
>
> diff --git a/man2/ioctl_userfaultfd.2 b/man2/ioctl_userfaultfd.2
> index d4a8375b8..d8380896a 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 +445,13 @@ 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
Break at the comma instead.
> +generate another write-protect userfault message.
> +This is only used in conjunction with write-protect mode when both missing and
"when both missing"
both what?
> +write-protect modes are enabled.
> .PP
> The
> .I copy
> @@ -654,6 +663,72 @@ 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
Break at the comma instead.
> +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
Break at the comma.
> +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.
> +.TP
> +.B ENOENT
> +The range specified in
> +.I range
> +is not valid.
> +For example, the virtual address does not exist, or not registered with
Better break at the comma.
> +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
>
--
Alejandro Colomar
Linux man-pages comaintainer; https://www.kernel.org/doc/man-pages/
http://www.alejandro-colomar.es/
