On Thu, May 14, 2026 at 05:29:31PM -0700, SeongJae Park wrote: > On Fri, 8 May 2026 16:55:16 +0100 "Kiryl Shutsemau (Meta)" <[email protected]> > wrote: > > > Preparatory patch for userfaultfd read-write protection (RWP). RWP > > extends userfaultfd protection from plain write-protection (WP) to > > full read-write protection: accesses to an RWP-protected range -- > > reads as well as writes -- trap through userfaultfd. > > > > RWP marks ranges by combining PAGE_NONE with the uffd PTE bit, so > > the flag is only meaningful when both primitives exist. A new > > CONFIG_USERFAULTFD_RWP Kconfig symbol auto-selects when CONFIG_64BIT, > > CONFIG_ARCH_HAS_PTE_PROTNONE, and CONFIG_HAVE_ARCH_USERFAULTFD_WP > > are all set; call sites that gate on the flag depend on the symbol. > > Elsewhere VM_UFFD_RWP aliases VM_NONE and every downstream check > > folds to dead code. > > > > Nothing sets the flag yet. > > > > Signed-off-by: Kiryl Shutsemau <[email protected]> > > Assisted-by: Claude:claude-opus-4-6 > > A silly but loud thought. Would it make more sense to put Signed-off-by: > after > Assisted-by: ?
I am not sure. I see it both ways in git log. And I don't have strong opinion on the order here. Keeping as is. > > --- > > Documentation/filesystems/proc.rst | 1 + > > fs/proc/task_mmu.c | 3 +++ > > include/linux/mm.h | 28 +++++++++++++++++---------- > > include/linux/userfaultfd_k.h | 31 +++++++++++++++++++++++++----- > > include/trace/events/mmflags.h | 7 +++++++ > > mm/Kconfig | 9 +++++++++ > > 6 files changed, 64 insertions(+), 15 deletions(-) > > > > diff --git a/Documentation/filesystems/proc.rst > > b/Documentation/filesystems/proc.rst > > index db6167befb7b..db28207c5290 100644 > > --- a/Documentation/filesystems/proc.rst > > +++ b/Documentation/filesystems/proc.rst > > @@ -607,6 +607,7 @@ encoded manner. The codes are the following: > > um userfaultfd missing tracking > > uw userfaultfd wr-protect tracking > > ui userfaultfd minor fault > > + ur userfaultfd read-write-protect tracking > > Yet another silly but loud thought. My first feeling on this was that this > reads like 'u'serfaultfd 'r'ead-protect. And was further thinking 'uf' for > just 'u'seffaultfd 'f'ault or 'up' for 'u'serfault-'p'rotect might make sense. > But ended up thinking this is too trivial and ain't really matter. I will keep it. It's "u" + the first distinguishing letter of the mode name. r distinguishes RWP from WP cleanly. > [...] > > diff --git a/mm/Kconfig b/mm/Kconfig > > index e8bf1e9e6ad9..ccf534a8cbc9 100644 > > --- a/mm/Kconfig > > +++ b/mm/Kconfig > > @@ -1347,6 +1347,15 @@ config HAVE_ARCH_USERFAULTFD_MINOR > > help > > Arch has userfaultfd minor fault support > > > > +config USERFAULTFD_RWP > > + def_bool y > > + depends on 64BIT && ARCH_HAS_PTE_PROTNONE && HAVE_ARCH_USERFAULTFD_WP > > + help > > + Userfaultfd read-write protection (UFFDIO_RWPROTECT) delivers a > > Seems UFFDIO_RWPROTECT will be introduced later. Would it make more sense to > add this config together with the patch? Okay, I will move later in the patchset. > > + userfaultfd notification on every access -- read or write -- to a > > + protected range, letting userspace observe the working set of a > > + process. > > + > > menuconfig USERFAULTFD > > bool "Enable userfaultfd() system call" > > depends on MMU > > -- > > 2.51.2 > > > > > > None of my comments is a blocker. > > Reviewed-by: SeongJae Park <[email protected]> Thanks! -- Kiryl Shutsemau / Kirill A. Shutemov
