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Message-ID: <CAJHvVchQF+9=TbhzJFhnwmfeT7e42=ReoFhqV_p+r-aOxifTXw@mail.gmail.com> Date: Thu, 9 Mar 2023 14:27:27 -0800 From: Axel Rasmussen <axelrasmussen@...gle.com> To: Mike Rapoport <rppt@...nel.org> Cc: Alexander Viro <viro@...iv.linux.org.uk>, Andrew Morton <akpm@...ux-foundation.org>, Hugh Dickins <hughd@...gle.com>, Jan Kara <jack@...e.cz>, "Liam R. Howlett" <Liam.Howlett@...cle.com>, Matthew Wilcox <willy@...radead.org>, Mike Kravetz <mike.kravetz@...cle.com>, Muchun Song <muchun.song@...ux.dev>, Nadav Amit <namit@...are.com>, Peter Xu <peterx@...hat.com>, Shuah Khan <shuah@...nel.org>, James Houghton <jthoughton@...gle.com>, linux-fsdevel@...r.kernel.org, linux-kernel@...r.kernel.org, linux-mm@...ck.org, linux-kselftest@...r.kernel.org Subject: Re: [PATCH v4 4/4] mm: userfaultfd: add UFFDIO_CONTINUE_MODE_WP to install WP PTEs On Thu, Mar 9, 2023 at 1:11 AM Mike Rapoport <rppt@...nel.org> wrote: > > On Wed, Mar 08, 2023 at 02:19:32PM -0800, Axel Rasmussen wrote: > > UFFDIO_COPY already has UFFDIO_COPY_MODE_WP, so when installing a new > > PTE to resolve a missing fault, one can install a write-protected one. > > This is useful when using UFFDIO_REGISTER_MODE_{MISSING,WP} in > > combination. > > > > This was motivated by testing HugeTLB HGM [1], and in particular its > > interaction with userfaultfd features. Existing userfaultfd code > > supports using WP and MINOR modes together (i.e. you can register an > > area with both enabled), but without this CONTINUE flag the combination > > is in practice unusable. > > > > So, add an analogous UFFDIO_CONTINUE_MODE_WP, which does the same thing > > as UFFDIO_COPY_MODE_WP, but for *minor* faults. > > > > Update the selftest to do some very basic exercising of the new flag. > > > > [1]: https://patchwork.kernel.org/project/linux-mm/cover/20230218002819.1486479-1-jthoughton@google.com/ > > > > Acked-by: Peter Xu <peterx@...hat.com> > > Signed-off-by: Axel Rasmussen <axelrasmussen@...gle.com> > > Acked-by: Mike Rapoport (IBM) <rppt@...nel.org> > > > --- > > fs/userfaultfd.c | 8 ++++++-- > > include/linux/userfaultfd_k.h | 3 ++- > > include/uapi/linux/userfaultfd.h | 7 +++++++ > > mm/userfaultfd.c | 5 +++-- > > tools/testing/selftests/mm/userfaultfd.c | 4 ++++ > > 5 files changed, 22 insertions(+), 5 deletions(-) > > > > diff --git a/include/uapi/linux/userfaultfd.h b/include/uapi/linux/userfaultfd.h > > index 005e5e306266..14059a0861bf 100644 > > --- a/include/uapi/linux/userfaultfd.h > > +++ b/include/uapi/linux/userfaultfd.h > > @@ -297,6 +297,13 @@ struct uffdio_writeprotect { > > struct uffdio_continue { > > struct uffdio_range range; > > #define UFFDIO_CONTINUE_MODE_DONTWAKE ((__u64)1<<0) > > + /* > > + * UFFDIO_CONTINUE_MODE_WP will map the page write protected on > > + * the fly. UFFDIO_CONTINUE_MODE_WP is available only if the > > + * write protected ioctl is implemented for the range > > + * according to the uffdio_register.ioctls. > > + */ > > +#define UFFDIO_CONTINUE_MODE_WP ((__u64)1<<1) > > Please add the description of the new flag to Documentation/ and to the > userfaultfd man pages. Funny enough, neither flag is mentioned in Documentation/ today - I'll add a short passage about both. Happy to update the man pages as well, I'll send that patch separately. Thanks for reviewing! > > > __u64 mode; > > > > /* > > -- > Sincerely yours, > Mike.
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