On Mon, Jan 25, 2021 at 5:44 PM Lokesh Gidra <lokeshgidra@xxxxxxxxxx> 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%25akpm@xxxxxxxxxxxxxxxxxxxx/ > [2] https://lore.kernel.org/linux-mm/20201215031354.gUsHJUpKo%25akpm@xxxxxxxxxxxxxxxxxxxx/ > > Signed-off-by: Lokesh Gidra <lokeshgidra@xxxxxxxxxx> > --- > 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 linux-mm@xxxxxxxxxxxxxxxx earlier. > 2.30.0.280.ga3ce27912f-goog >
