Re: [PATCH v3 3/3] selftests/mm: add UFFDIO_MOVE ioctl test

[Suren Baghdasaryan]

On Thu, Oct 12, 2023 at 3:29 PM Peter Xu <peterx@xxxxxxxxxx> wrote:
>
> On Sun, Oct 08, 2023 at 11:42:28PM -0700, Suren Baghdasaryan wrote:
> > Add a test for new UFFDIO_MOVE ioctl which uses uffd to move source
> > into destination buffer while checking the contents of both after
> > remapping. After the operation the content of the destination buffer
> > should match the original source buffer's content while the source
> > buffer should be zeroed.
> >
> > Signed-off-by: Suren Baghdasaryan <surenb@xxxxxxxxxx>
> > ---
> >  tools/testing/selftests/mm/uffd-common.c     | 41 ++++++++++++-
> >  tools/testing/selftests/mm/uffd-common.h     |  1 +
> >  tools/testing/selftests/mm/uffd-unit-tests.c | 62 ++++++++++++++++++++
> >  3 files changed, 102 insertions(+), 2 deletions(-)
> >
> > diff --git a/tools/testing/selftests/mm/uffd-common.c b/tools/testing/selftests/mm/uffd-common.c
> > index 02b89860e193..ecc1244f1c2b 100644
> > --- a/tools/testing/selftests/mm/uffd-common.c
> > +++ b/tools/testing/selftests/mm/uffd-common.c
> > @@ -52,6 +52,13 @@ static int anon_allocate_area(void **alloc_area, bool is_src)
> >               *alloc_area = NULL;
> >               return -errno;
> >       }
> > +
> > +     /* Prevent source pages from collapsing into THPs */
> > +     if (madvise(*alloc_area, nr_pages * page_size, MADV_NOHUGEPAGE)) {
> > +             *alloc_area = NULL;
> > +             return -errno;
> > +     }
>
> Can we move this to test specific code?

Ack. I think that's doable.

>
> > +
> >       return 0;
> >  }
> >
> > @@ -484,8 +491,14 @@ void uffd_handle_page_fault(struct uffd_msg *msg, struct uffd_args *args)
> >               offset = (char *)(unsigned long)msg->arg.pagefault.address - area_dst;
> >               offset &= ~(page_size-1);
> >
> > -             if (copy_page(uffd, offset, args->apply_wp))
> > -                     args->missing_faults++;
> > +             /* UFFD_MOVE is supported for anon non-shared mappings. */
> > +             if (uffd_test_ops == &anon_uffd_test_ops && !map_shared) {
>
> IIUC this means move_page() will start to run on many other tests... as
> long as anonymous & private.  Probably not wanted, because not all tests
> may need this MOVE test, and it also means UFFDIO_COPY is never tested on
> anonymous..
>
> You can overwrite uffd_args.handle_fault().  Axel just added a hook which
> seems also usable here.  See 99aa77215ad02.

Yes, I was thinking about adding a completely new set of tests for
UFFDIO_MOVE but was not sure. With your confirmation I'll follow that
path so that UFFDIO_COPY tests stay the same.

>
> > +                     if (move_page(uffd, offset))
> > +                             args->missing_faults++;
> > +             } else {
> > +                     if (copy_page(uffd, offset, args->apply_wp))
> > +                             args->missing_faults++;
> > +             }
> >       }
> >  }
> >
> > @@ -620,6 +633,30 @@ int copy_page(int ufd, unsigned long offset, bool wp)
> >       return __copy_page(ufd, offset, false, wp);
> >  }
> >
> > +int move_page(int ufd, unsigned long offset)
> > +{
> > +     struct uffdio_move uffdio_move;
> > +
> > +     if (offset >= nr_pages * page_size)
> > +             err("unexpected offset %lu\n", offset);
> > +     uffdio_move.dst = (unsigned long) area_dst + offset;
> > +     uffdio_move.src = (unsigned long) area_src + offset;
> > +     uffdio_move.len = page_size;
> > +     uffdio_move.mode = UFFDIO_MOVE_MODE_ALLOW_SRC_HOLES;
> > +     uffdio_move.move = 0;
> > +     if (ioctl(ufd, UFFDIO_MOVE, &uffdio_move)) {
> > +             /* real retval in uffdio_move.move */
> > +             if (uffdio_move.move != -EEXIST)
> > +                     err("UFFDIO_MOVE error: %"PRId64,
> > +                         (int64_t)uffdio_move.move);
> > +             wake_range(ufd, uffdio_move.dst, page_size);
> > +     } else if (uffdio_move.move != page_size) {
> > +             err("UFFDIO_MOVE error: %"PRId64, (int64_t)uffdio_move.move);
> > +     } else
> > +             return 1;
> > +     return 0;
> > +}
> > +
> >  int uffd_open_dev(unsigned int flags)
> >  {
> >       int fd, uffd;
> > diff --git a/tools/testing/selftests/mm/uffd-common.h b/tools/testing/selftests/mm/uffd-common.h
> > index 7c4fa964c3b0..f4d79e169a3d 100644
> > --- a/tools/testing/selftests/mm/uffd-common.h
> > +++ b/tools/testing/selftests/mm/uffd-common.h
> > @@ -111,6 +111,7 @@ void wp_range(int ufd, __u64 start, __u64 len, bool wp);
> >  void uffd_handle_page_fault(struct uffd_msg *msg, struct uffd_args *args);
> >  int __copy_page(int ufd, unsigned long offset, bool retry, bool wp);
> >  int copy_page(int ufd, unsigned long offset, bool wp);
> > +int move_page(int ufd, unsigned long offset);
> >  void *uffd_poll_thread(void *arg);
> >
> >  int uffd_open_dev(unsigned int flags);
> > diff --git a/tools/testing/selftests/mm/uffd-unit-tests.c b/tools/testing/selftests/mm/uffd-unit-tests.c
> > index 2709a34a39c5..f0ded3b34367 100644
> > --- a/tools/testing/selftests/mm/uffd-unit-tests.c
> > +++ b/tools/testing/selftests/mm/uffd-unit-tests.c
> > @@ -824,6 +824,10 @@ static void uffd_events_test_common(bool wp)
> >       char c;
> >       struct uffd_args args = { 0 };
> >
> > +     /* Prevent source pages from being mapped more than once */
> > +     if (madvise(area_src, nr_pages * page_size, MADV_DONTFORK))
> > +             err("madvise(MADV_DONTFORK) failed");
>
> Modifying events test is weird.. I assume you don't need this anymore after
> you switch to the handle_fault() hook.

I think so but let me try first and I'll get back on that.

>
> > +
> >       fcntl(uffd, F_SETFL, uffd_flags | O_NONBLOCK);
> >       if (uffd_register(uffd, area_dst, nr_pages * page_size,
> >                         true, wp, false))
> > @@ -1062,6 +1066,58 @@ static void uffd_poison_test(uffd_test_args_t *targs)
> >       uffd_test_pass();
> >  }
> >
> > +static void uffd_move_test(uffd_test_args_t *targs)
> > +{
> > +     unsigned long nr;
> > +     pthread_t uffd_mon;
> > +     char c;
> > +     unsigned long long count;
> > +     struct uffd_args args = { 0 };
> > +
> > +     if (uffd_register(uffd, area_dst, nr_pages * page_size,
> > +                       true, false, false))
> > +             err("register failure");
> > +
> > +     if (pthread_create(&uffd_mon, NULL, uffd_poll_thread, &args))
> > +             err("uffd_poll_thread create");
> > +
> > +     /*
> > +      * Read each of the pages back using the UFFD-registered mapping. We
> > +      * expect that the first time we touch a page, it will result in a missing
> > +      * fault. uffd_poll_thread will resolve the fault by remapping source
> > +      * page to destination.
> > +      */
> > +     for (nr = 0; nr < nr_pages; nr++) {
> > +             /* Check area_src content */
> > +             count = *area_count(area_src, nr);
> > +             if (count != count_verify[nr])
> > +                     err("nr %lu source memory invalid %llu %llu\n",
> > +                         nr, count, count_verify[nr]);
> > +
> > +             /* Faulting into area_dst should remap the page */
> > +             count = *area_count(area_dst, nr);
> > +             if (count != count_verify[nr])
> > +                     err("nr %lu memory corruption %llu %llu\n",
> > +                         nr, count, count_verify[nr]);
> > +
> > +             /* Re-check area_src content which should be empty */
> > +             count = *area_count(area_src, nr);
> > +             if (count != 0)
> > +                     err("nr %lu move failed %llu %llu\n",
> > +                         nr, count, count_verify[nr]);
>
> All of above should see zeros, right?  Because I don't think anyone boosted
> the counter at all..
>
> Maybe set some non-zero values to it?  Then the re-check can make more
> sense.

I thought uffd_test_ctx_init() is initializing area_count(area_src,
nr), so the source pages should contain non-zero data before the move.
Am I missing something?

>
> If you want, I think we can also make uffd-stress.c test to cover MOVE too,
> basically replacing all UFFDIO_COPY when e.g. user specified from cmdline.
> Optional, and may need some touch ups here and there, though.

That's a good idea. I'll add that in the next version.
Thanks,
Suren.

>
> Thanks,
>
> > +     }
> > +
> > +     if (write(pipefd[1], &c, sizeof(c)) != sizeof(c))
> > +             err("pipe write");
> > +     if (pthread_join(uffd_mon, NULL))
> > +             err("join() failed");
> > +
> > +     if (args.missing_faults != nr_pages || args.minor_faults != 0)
> > +             uffd_test_fail("stats check error");
> > +     else
> > +             uffd_test_pass();
> > +}
> > +
> >  /*
> >   * Test the returned uffdio_register.ioctls with different register modes.
> >   * Note that _UFFDIO_ZEROPAGE is tested separately in the zeropage test.
> > @@ -1139,6 +1195,12 @@ uffd_test_case_t uffd_tests[] = {
> >               .mem_targets = MEM_ALL,
> >               .uffd_feature_required = 0,
> >       },
> > +     {
> > +             .name = "move",
> > +             .uffd_fn = uffd_move_test,
> > +             .mem_targets = MEM_ANON,
> > +             .uffd_feature_required = UFFD_FEATURE_MOVE,
> > +     },
> >       {
> >               .name = "wp-fork",
> >               .uffd_fn = uffd_wp_fork_test,
> > --
> > 2.42.0.609.gbb76f46606-goog
> >
>
> --
> Peter Xu
>
> --
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