Add description of UFFD_USER_MODE_ONLY flag to userfaultfd(2) manual
page, which is required after [1]. Also updated the description of
unprivileged_userfaultfd file in proc(5) as per [2].
[1] https://lore.kernel.org/linux-mm/20201215031349.NXimL388W%[email protected]/
[2] https://lore.kernel.org/linux-mm/20201215031354.gUsHJUpKo%[email protected]/
Signed-off-by: Lokesh Gidra <[email protected]>
---
man2/userfaultfd.2 | 5 +++++
man5/proc.5 | 12 ++++++++++++
2 files changed, 17 insertions(+)
diff --git a/man2/userfaultfd.2 b/man2/userfaultfd.2
index e7dc9f813..792a49d52 100644
--- a/man2/userfaultfd.2
+++ b/man2/userfaultfd.2
@@ -72,6 +72,11 @@ See the description of the
.BR O_NONBLOCK
flag in
.BR open (2).
+.TP
+.BR UFFD_USER_MODE_ONLY " (Since Linux 5.11)"
+Allow handling of user-mode page-faults only. See the description of the
+unprivileged_userfaultfd file in
+.BR proc (5).
.PP
When the last file descriptor referring to a userfaultfd object is closed,
all memory ranges that were registered with the object are unregistered
diff --git a/man5/proc.5 b/man5/proc.5
index f16a29d6e..cb2350c0c 100644
--- a/man5/proc.5
+++ b/man5/proc.5
@@ -5905,6 +5905,18 @@ If this file has the value 0, then only processes that have the
capability may employ
.BR userfaultfd (2).
The default value in this file is 1.
+.IP
+Starting with Linux 5.11,
+.BR userfaultfd (2)
+can be used by all processes, however, if this file has the value 0, then
+.BR UFFD_USER_MODE_ONLY
+flag must be passed to it, which restricts page-fault handling to only
+user-mode faults. This restriction is not applicable for processes with
+.B CAP_SYS_PTRACE
+capability, or if this file has the value 1. Furthermore, the default
+value in this file is changed to 0. For further details see the
+Linux kernel source file
+.I Documentation/admin\-guide/sysctl/vm.rst.
.TP
.IR /proc/sysrq\-trigger " (since Linux 2.4.21)"
Writing a character to this file triggers the same SysRq function as
--
2.30.0.280.ga3ce27912f-goog
On Mon, Jan 25, 2021 at 5:44 PM Lokesh Gidra <[email protected]> wrote:
>
> Add description of UFFD_USER_MODE_ONLY flag to userfaultfd(2) manual
> page, which is required after [1]. Also updated the description of
> unprivileged_userfaultfd file in proc(5) as per [2].
>
> [1] https://lore.kernel.org/linux-mm/20201215031349.NXimL388W%[email protected]/
> [2] https://lore.kernel.org/linux-mm/20201215031354.gUsHJUpKo%[email protected]/
>
> Signed-off-by: Lokesh Gidra <[email protected]>
> ---
> man2/userfaultfd.2 | 5 +++++
> man5/proc.5 | 12 ++++++++++++
> 2 files changed, 17 insertions(+)
>
> diff --git a/man2/userfaultfd.2 b/man2/userfaultfd.2
> index e7dc9f813..792a49d52 100644
> --- a/man2/userfaultfd.2
> +++ b/man2/userfaultfd.2
> @@ -72,6 +72,11 @@ See the description of the
> .BR O_NONBLOCK
> flag in
> .BR open (2).
> +.TP
> +.BR UFFD_USER_MODE_ONLY " (Since Linux 5.11)"
> +Allow handling of user-mode page-faults only. See the description of the
> +unprivileged_userfaultfd file in
> +.BR proc (5).
> .PP
> When the last file descriptor referring to a userfaultfd object is closed,
> all memory ranges that were registered with the object are unregistered
> diff --git a/man5/proc.5 b/man5/proc.5
> index f16a29d6e..cb2350c0c 100644
> --- a/man5/proc.5
> +++ b/man5/proc.5
> @@ -5905,6 +5905,18 @@ If this file has the value 0, then only processes that have the
> capability may employ
> .BR userfaultfd (2).
> The default value in this file is 1.
> +.IP
> +Starting with Linux 5.11,
> +.BR userfaultfd (2)
> +can be used by all processes, however, if this file has the value 0, then
> +.BR UFFD_USER_MODE_ONLY
> +flag must be passed to it, which restricts page-fault handling to only
> +user-mode faults. This restriction is not applicable for processes with
> +.B CAP_SYS_PTRACE
> +capability, or if this file has the value 1. Furthermore, the default
> +value in this file is changed to 0. For further details see the
> +Linux kernel source file
> +.I Documentation/admin\-guide/sysctl/vm.rst.
> .TP
> .IR /proc/sysrq\-trigger " (since Linux 2.4.21)"
> Writing a character to this file triggers the same SysRq function as
> --
Adding the right linux-mm mailing list. Mistakenly used
[email protected] earlier.
> 2.30.0.280.ga3ce27912f-goog
>