[PATCH 0/2] userfaultfd.2: Update to latest

[PATCH 0/2] userfaultfd.2: Update to latest

[Peter Xu]

Add the two missing pieces till latest 5.19-rc1: the UFFD_USER_MODE_ONLY
flag, and also the recent wr-protect support on shmem and hugetlbfs.

Please review, thanks.

Peter Xu (2):
  userfaultfd.2: Add section for UFFD_USER_MODE_ONLY
  userfaultfd.2: Update on write-protection support

 man2/userfaultfd.2 | 22 +++++++++++++++++-----
 1 file changed, 17 insertions(+), 5 deletions(-)

-- 
2.32.0

[PATCH 1/2] userfaultfd.2: Add section for UFFD_USER_MODE_ONLY

[Peter Xu]

Add a paragraph for UFFD_USER_MODE_ONLY flag that was introduced in
Linux 5.11.

Signed-off-by: Peter Xu <peterx@redhat.com>
---
 man2/userfaultfd.2 | 14 ++++++++++++--
 1 file changed, 12 insertions(+), 2 deletions(-)

diff --git a/man2/userfaultfd.2 b/man2/userfaultfd.2
index cee7c01d2..0928a76d2 100644
--- a/man2/userfaultfd.2
+++ b/man2/userfaultfd.2
@@ -29,8 +29,9 @@
 userfaultfd \- create a file descriptor for handling page faults in user space
 .SH SYNOPSIS
 .nf
-.BR "#include <fcntl.h>" "            /* Definition of " O_* " constants */"
-.BR "#include <sys/syscall.h>" "      /* Definition of " SYS_* " constants */"
+.BR "#include <fcntl.h>" "             /* Definition of " O_* " constants */"
+.BR "#include <sys/syscall.h>" "       /* Definition of " SYS_* " constants */"
+.BR "#include <linux/userfaultfd.h>" " /* Definition of " UFFD_* " constants */"
 .B #include <unistd.h>
 .PP
 .BI "int syscall(SYS_userfaultfd, int " flags );
@@ -76,6 +77,15 @@ See the description of the
 .BR O_NONBLOCK
 flag in
 .BR open (2).
+.TP
+.BR UFFD_USER_MODE_ONLY
+This is an userfaultfd specific flag that was introduced since Linux 5.11.
+When set, the userfaultfd object will only be able to handle page faults
+originated from the userspace on the registered regions.
+When a kernel originated fault was triggered on the registered range with
+this userfaultfd, a
+.BR SIGBUS
+signal will be delivered.
 .PP
 When the last file descriptor referring to a userfaultfd object is closed,
 all memory ranges that were registered with the object are unregistered
-- 
2.32.0

[PATCH 2/2] userfaultfd.2: Update on write-protection support

[Peter Xu]

The shmem/hugetlbfs memory types are supported for write-protection
messages very lately.  Update the man page to reflect that.

Signed-off-by: Peter Xu <peterx@redhat.com>
---
 man2/userfaultfd.2 | 8 +++++---
 1 file changed, 5 insertions(+), 3 deletions(-)

diff --git a/man2/userfaultfd.2 b/man2/userfaultfd.2
index 0928a76d2..99aae8b50 100644
--- a/man2/userfaultfd.2
+++ b/man2/userfaultfd.2
@@ -273,13 +273,17 @@ Since Linux 4.11,
 userfaultfd can be also used with hugetlbfs and shared memory mappings.
 .\"
 .SS Userfaultfd write-protect mode (since 5.7)
-Since Linux 5.7, userfaultfd supports write-protect mode.
+Since Linux 5.7, userfaultfd supports write-protect mode for anonymous memory.
 The user needs to first check availability of this feature using
 .B UFFDIO_API
 ioctl against the feature bit
 .B UFFD_FEATURE_PAGEFAULT_FLAG_WP
 before using this feature.
 .PP
+Since Linux 5.19, the write-protection mode was also supported on shmem and hugetlbfs
+memory types. It can be detected with the feature bit
+.BR UFFD_FEATURE_WP_HUGETLBFS_SHMEM .
+.PP
 To register with userfaultfd write-protect mode, the user needs to initiate the
 .B UFFDIO_REGISTER
 ioctl with mode
@@ -330,8 +334,6 @@ ioctl, whose
 should have the flag
 .B UFFDIO_WRITEPROTECT_MODE_WP
 cleared upon the faulted page or range.
-.PP
-Write-protect mode supports only private anonymous memory.
 .SS Reading from the userfaultfd structure
 Each
 .BR read (2)
-- 
2.32.0

Re: [PATCH 1/2] userfaultfd.2: Add section for UFFD_USER_MODE_ONLY

[Alejandro Colomar]

[-- Attachment #1.1: Type: text/plain, Size: 2229 bytes --]

Hi Peter,

On 5/31/22 03:11, Peter Xu wrote:
> Add a paragraph for UFFD_USER_MODE_ONLY flag that was introduced in
> Linux 5.11.
> 
> Signed-off-by: Peter Xu <peterx@redhat.com>

See some minor comments below.

Cheers,

Alex

> ---
>   man2/userfaultfd.2 | 14 ++++++++++++--
>   1 file changed, 12 insertions(+), 2 deletions(-)
> 
> diff --git a/man2/userfaultfd.2 b/man2/userfaultfd.2
> index cee7c01d2..0928a76d2 100644
> --- a/man2/userfaultfd.2
> +++ b/man2/userfaultfd.2
> @@ -29,8 +29,9 @@
>   userfaultfd \- create a file descriptor for handling page faults in user space
>   .SH SYNOPSIS
>   .nf
> -.BR "#include <fcntl.h>" "            /* Definition of " O_* " constants */"
> -.BR "#include <sys/syscall.h>" "      /* Definition of " SYS_* " constants */"
> +.BR "#include <fcntl.h>" "             /* Definition of " O_* " constants */"
> +.BR "#include <sys/syscall.h>" "       /* Definition of " SYS_* " constants */"
> +.BR "#include <linux/userfaultfd.h>" " /* Definition of " UFFD_* " constants */"
>   .B #include <unistd.h>
>   .PP
>   .BI "int syscall(SYS_userfaultfd, int " flags );
> @@ -76,6 +77,15 @@ See the description of the
>   .BR O_NONBLOCK
>   flag in
>   .BR open (2).
> +.TP
> +.BR UFFD_USER_MODE_ONLY


s/BR/B/

see groff_man(7):

[
	[...]

        .B [text]
               Set text in bold.  If the macro is given no  argu‐
               ments,  the  text of the next input line is set in
               bold.

	[...]

        .BR bold‐text roman‐text ...
               Set each argument in bold and roman, alternately.
]

> +This is an userfaultfd specific flag that was introduced since Linux 5.11.
> +When set, the userfaultfd object will only be able to handle page faults
> +originated from the userspace on the registered regions.
> +When a kernel originated fault was triggered on the registered range with
> +this userfaultfd, a
> +.BR SIGBUS

s/BR/B/

> +signal will be delivered.
>   .PP
>   When the last file descriptor referring to a userfaultfd object is closed,
>   all memory ranges that were registered with the object are unregistered

-- 
Alejandro Colomar
<http://www.alejandro-colomar.es/>

[-- Attachment #2: OpenPGP digital signature --]
[-- Type: application/pgp-signature, Size: 833 bytes --]

Re: [PATCH 2/2] userfaultfd.2: Update on write-protection support

[Alejandro Colomar]

[-- Attachment #1.1: Type: text/plain, Size: 2269 bytes --]

Hi Peter,

On 5/31/22 03:11, Peter Xu wrote:
> The shmem/hugetlbfs memory types are supported for write-protection
> messages very lately.  Update the man page to reflect that.
> 
> Signed-off-by: Peter Xu <peterx@redhat.com>

Please see some source formatting comments below.

Cheers,

Alex

> ---
>   man2/userfaultfd.2 | 8 +++++---
>   1 file changed, 5 insertions(+), 3 deletions(-)
> 
> diff --git a/man2/userfaultfd.2 b/man2/userfaultfd.2
> index 0928a76d2..99aae8b50 100644
> --- a/man2/userfaultfd.2
> +++ b/man2/userfaultfd.2
> @@ -273,13 +273,17 @@ Since Linux 4.11,
>   userfaultfd can be also used with hugetlbfs and shared memory mappings.
>   .\"
>   .SS Userfaultfd write-protect mode (since 5.7)
> -Since Linux 5.7, userfaultfd supports write-protect mode.
> +Since Linux 5.7, userfaultfd supports write-protect mode for anonymous memory.
>   The user needs to first check availability of this feature using
>   .B UFFDIO_API
>   ioctl against the feature bit
>   .B UFFD_FEATURE_PAGEFAULT_FLAG_WP
>   before using this feature.
>   .PP
> +Since Linux 5.19, the write-protection mode was also supported on shmem and hugetlbfs
> +memory types. It can be detected with the feature bit

See man-pages(7):

[
    Use semantic newlines
        In the source of a manual page, new sentences  should  be
        started  on new lines, and long sentences should be split
        into lines at clause breaks (commas, semicolons,  colons,
        and  so on).  This convention, sometimes known as "seman‐
        tic newlines", makes it  easier  to  see  the  effect  of
        patches,  which  often operate at the level of individual
        sentences or sentence clauses.
]

> +.BR UFFD_FEATURE_WP_HUGETLBFS_SHMEM .
> +.PP
>   To register with userfaultfd write-protect mode, the user needs to initiate the
>   .B UFFDIO_REGISTER
>   ioctl with mode
> @@ -330,8 +334,6 @@ ioctl, whose
>   should have the flag
>   .B UFFDIO_WRITEPROTECT_MODE_WP
>   cleared upon the faulted page or range.
> -.PP
> -Write-protect mode supports only private anonymous memory.
>   .SS Reading from the userfaultfd structure
>   Each
>   .BR read (2)

-- 
Alejandro Colomar
<http://www.alejandro-colomar.es/>

[-- Attachment #2: OpenPGP digital signature --]
[-- Type: application/pgp-signature, Size: 833 bytes --]

Re: [PATCH 1/2] userfaultfd.2: Add section for UFFD_USER_MODE_ONLY

[Peter Xu]

On Fri, Jun 03, 2022 at 07:11:05PM +0200, Alejandro Colomar wrote:
> Hi Peter,
> 
> On 5/31/22 03:11, Peter Xu wrote:
> > Add a paragraph for UFFD_USER_MODE_ONLY flag that was introduced in
> > Linux 5.11.
> > 
> > Signed-off-by: Peter Xu <peterx@redhat.com>
> 
> See some minor comments below.
> 
> Cheers,
> 
> Alex
> 
> > ---
> >   man2/userfaultfd.2 | 14 ++++++++++++--
> >   1 file changed, 12 insertions(+), 2 deletions(-)
> > 
> > diff --git a/man2/userfaultfd.2 b/man2/userfaultfd.2
> > index cee7c01d2..0928a76d2 100644
> > --- a/man2/userfaultfd.2
> > +++ b/man2/userfaultfd.2
> > @@ -29,8 +29,9 @@
> >   userfaultfd \- create a file descriptor for handling page faults in user space
> >   .SH SYNOPSIS
> >   .nf
> > -.BR "#include <fcntl.h>" "            /* Definition of " O_* " constants */"
> > -.BR "#include <sys/syscall.h>" "      /* Definition of " SYS_* " constants */"
> > +.BR "#include <fcntl.h>" "             /* Definition of " O_* " constants */"
> > +.BR "#include <sys/syscall.h>" "       /* Definition of " SYS_* " constants */"
> > +.BR "#include <linux/userfaultfd.h>" " /* Definition of " UFFD_* " constants */"
> >   .B #include <unistd.h>
> >   .PP
> >   .BI "int syscall(SYS_userfaultfd, int " flags );
> > @@ -76,6 +77,15 @@ See the description of the
> >   .BR O_NONBLOCK
> >   flag in
> >   .BR open (2).
> > +.TP
> > +.BR UFFD_USER_MODE_ONLY
> 
> 
> s/BR/B/
> 
> see groff_man(7):
> 
> [
> 	[...]
> 
>        .B [text]
>               Set text in bold.  If the macro is given no  argu‐
>               ments,  the  text of the next input line is set in
>               bold.
> 
> 	[...]
> 
>        .BR bold‐text roman‐text ...
>               Set each argument in bold and roman, alternately.
> ]
> 
> > +This is an userfaultfd specific flag that was introduced since Linux 5.11.
> > +When set, the userfaultfd object will only be able to handle page faults
> > +originated from the userspace on the registered regions.
> > +When a kernel originated fault was triggered on the registered range with
> > +this userfaultfd, a
> > +.BR SIGBUS
> 
> s/BR/B/

Thanks Alex, I'll fix and repost the patchset soon.

-- 
Peter Xu