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Message-ID: <CAJHvVchqCBsiZVuMc2b3jBgpeK+9LTp6tB-LBDrrcGkmjQqmLQ@mail.gmail.com>
Date: Wed, 17 Aug 2022 12:53:00 -0700
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>,
Dave Hansen <dave.hansen@...ux.intel.com>,
"Dmitry V . Levin" <ldv@...linux.org>,
Gleb Fotengauer-Malinovskiy <glebfm@...linux.org>,
Hugh Dickins <hughd@...gle.com>, Jan Kara <jack@...e.cz>,
Jonathan Corbet <corbet@....net>,
Mel Gorman <mgorman@...hsingularity.net>,
Mike Kravetz <mike.kravetz@...cle.com>,
Nadav Amit <namit@...are.com>, Peter Xu <peterx@...hat.com>,
Shuah Khan <shuah@...nel.org>,
Suren Baghdasaryan <surenb@...gle.com>,
Vlastimil Babka <vbabka@...e.cz>,
zhangyi <yi.zhang@...wei.com>, linux-doc@...r.kernel.org,
linux-fsdevel <linux-fsdevel@...r.kernel.org>,
LKML <linux-kernel@...r.kernel.org>,
Linuxkselftest <linux-kselftest@...r.kernel.org>,
Linux MM <linux-mm@...ck.org>,
linux-security-module@...r.kernel.org
Subject: Re: [PATCH v5 3/5] userfaultfd: selftests: modify selftest to use /dev/userfaultfd
On Wed, Aug 10, 2022 at 11:38 PM Mike Rapoport <rppt@...nel.org> wrote:
>
> On Mon, Aug 08, 2022 at 10:56:12AM -0700, Axel Rasmussen wrote:
> > We clearly want to ensure both userfaultfd(2) and /dev/userfaultfd keep
> > working into the future, so just run the test twice, using each
> > interface.
> >
> > Instead of always testing both userfaultfd(2) and /dev/userfaultfd,
> > let the user choose which to test.
> >
> > As with other test features, change the behavior based on a new
> > command line flag. Introduce the idea of "test mods", which are
> > generic (not specific to a test type) modifications to the behavior of
> > the test. This is sort of borrowed from this RFC patch series [1], but
> > simplified a bit.
> >
> > The benefit is, in "typical" configurations this test is somewhat slow
> > (say, 30sec or something). Testing both clearly doubles it, so it may
> > not always be desirable, as users are likely to use one or the other,
> > but never both, in the "real world".
> >
> > [1]: https://patchwork.kernel.org/project/linux-mm/patch/20201129004548.1619714-14-namit@vmware.com/
> >
> > Acked-by: Peter Xu <peterx@...hat.com>
> > Signed-off-by: Axel Rasmussen <axelrasmussen@...gle.com>
>
> With a few nits below
>
> Acked-by: Mike Rapoport <rppt@...ux.ibm.com>
Thanks for reviewing, Mike!
>
> > ---
> > tools/testing/selftests/vm/userfaultfd.c | 69 ++++++++++++++++++++----
> > 1 file changed, 60 insertions(+), 9 deletions(-)
> >
> > diff --git a/tools/testing/selftests/vm/userfaultfd.c b/tools/testing/selftests/vm/userfaultfd.c
> > index 7c3f1b0ab468..cae72867c173 100644
> > --- a/tools/testing/selftests/vm/userfaultfd.c
> > +++ b/tools/testing/selftests/vm/userfaultfd.c
> > @@ -77,6 +77,11 @@ static int bounces;
> > #define TEST_SHMEM 3
> > static int test_type;
> >
> > +#define UFFD_FLAGS (O_CLOEXEC | O_NONBLOCK | UFFD_USER_MODE_ONLY)
> > +
> > +/* test using /dev/userfaultfd, instead of userfaultfd(2) */
> > +static bool test_dev_userfaultfd;
> > +
> > /* exercise the test_uffdio_*_eexist every ALARM_INTERVAL_SECS */
> > #define ALARM_INTERVAL_SECS 10
> > static volatile bool test_uffdio_copy_eexist = true;
> > @@ -125,6 +130,8 @@ struct uffd_stats {
> > const char *examples =
> > "# Run anonymous memory test on 100MiB region with 99999 bounces:\n"
> > "./userfaultfd anon 100 99999\n\n"
> > + "# Run the same anonymous memory test, but using /dev/userfaultfd:\n"
> > + "./userfaultfd anon:dev 100 99999\n\n"
> > "# Run share memory test on 1GiB region with 99 bounces:\n"
> > "./userfaultfd shmem 1000 99\n\n"
> > "# Run hugetlb memory test on 256MiB region with 50 bounces:\n"
> > @@ -141,6 +148,14 @@ static void usage(void)
> > "[hugetlbfs_file]\n\n");
> > fprintf(stderr, "Supported <test type>: anon, hugetlb, "
> > "hugetlb_shared, shmem\n\n");
> > + fprintf(stderr, "'Test mods' can be joined to the test type string with a ':'. "
> > + "Supported mods:\n");
> > + fprintf(stderr, "\tsyscall - Use userfaultfd(2) (default)\n");
> > + fprintf(stderr, "\tdev - Use /dev/userfaultfd instead of userfaultfd(2)\n");
> > + fprintf(stderr, "\nExample test mod usage:\n");
> > + fprintf(stderr, "# Run anonymous memory test with /dev/userfaultfd:\n");
> > + fprintf(stderr, "./userfaultfd anon:dev 100 99999\n\n");
> > +
> > fprintf(stderr, "Examples:\n\n");
> > fprintf(stderr, "%s", examples);
> > exit(1);
> > @@ -154,12 +169,14 @@ static void usage(void)
> > ret, __LINE__); \
> > } while (0)
> >
> > -#define err(fmt, ...) \
> > +#define errexit(exitcode, fmt, ...) \
> > do { \
> > _err(fmt, ##__VA_ARGS__); \
> > - exit(1); \
> > + exit(exitcode); \
> > } while (0)
> >
> > +#define err(fmt, ...) errexit(1, fmt, ##__VA_ARGS__)
> > +
> > static void uffd_stats_reset(struct uffd_stats *uffd_stats,
> > unsigned long n_cpus)
> > {
> > @@ -383,13 +400,29 @@ static void assert_expected_ioctls_present(uint64_t mode, uint64_t ioctls)
> > }
> > }
> >
> > +static int __userfaultfd_open_dev(void)
> > +{
> > + int fd, _uffd = -1;
>
> Nit: the initialization here is not necessary, _uffd is always set from
> ioctl() return value.
Agreed.
>
> > +
> > + fd = open("/dev/userfaultfd", O_RDWR | O_CLOEXEC);
> > + if (fd < 0)
> > + return -1;
> > +
> > + _uffd = ioctl(fd, USERFAULTFD_IOC_NEW, UFFD_FLAGS);
> > + close(fd);
> > + return _uffd;
> > +}
> > +
> > static void userfaultfd_open(uint64_t *features)
> > {
> > struct uffdio_api uffdio_api;
> >
> > - uffd = syscall(__NR_userfaultfd, O_CLOEXEC | O_NONBLOCK | UFFD_USER_MODE_ONLY);
> > + if (test_dev_userfaultfd)
> > + uffd = __userfaultfd_open_dev();
> > + else
> > + uffd = syscall(__NR_userfaultfd, UFFD_FLAGS);
> > if (uffd < 0)
> > - err("userfaultfd syscall not available in this kernel");
> > + errexit(KSFT_SKIP, "creating userfaultfd failed");
>
> I'm not sure if this should be KSFT_SKIP. If creation of uffd failed
> because anything except ENOSYS I'd consider the test failing.
Agreed, but looking at it I think it's more complicated.
In __userfaultfd_open_dev, I think:
- If we fail to open /dev/userfaultfd for any reason, that's a KSFT_SKIP
- If USERFAULTFD_IOC_NEW returns ENOTTY that's a KSFT_SKIP, otherwise
a real test failure.
But then for syscall(__NR_userfaultfd, ...), I think ENOSYS is a
KSFT_SKIP, but any other errno is a real test failure.
I'll send an updated version which has those semantics. I think to do
so we need to move some of the error handling into
__userfaultfd_open_dev, instead of having its caller do it.
>
> > uffd_flags = fcntl(uffd, F_GETFD, NULL);
> >
> > uffdio_api.api = UFFD_API;
> > @@ -1584,8 +1617,6 @@ unsigned long default_huge_page_size(void)
> >
> > static void set_test_type(const char *type)
> > {
> > - uint64_t features = UFFD_API_FEATURES;
> > -
> > if (!strcmp(type, "anon")) {
> > test_type = TEST_ANON;
> > uffd_test_ops = &anon_uffd_test_ops;
> > @@ -1603,9 +1634,29 @@ static void set_test_type(const char *type)
> > test_type = TEST_SHMEM;
> > uffd_test_ops = &shmem_uffd_test_ops;
> > test_uffdio_minor = true;
> > - } else {
> > - err("Unknown test type: %s", type);
> > }
> > +}
> > +
> > +static void parse_test_type_arg(const char *raw_type)
> > +{
> > + char *buf = strdup(raw_type);
> > + uint64_t features = UFFD_API_FEATURES;
> > +
> > + while (buf) {
> > + const char *token = strsep(&buf, ":");
> > +
> > + if (!test_type)
> > + set_test_type(token);
> > + else if (!strcmp(token, "dev"))
> > + test_dev_userfaultfd = true;
> > + else if (!strcmp(token, "syscall"))
> > + test_dev_userfaultfd = false;
> > + else
> > + err("unrecognized test mod '%s'", token);
> > + }
> > +
> > + if (!test_type)
> > + err("failed to parse test type argument: '%s'", raw_type);
> >
> > if (test_type == TEST_HUGETLB)
> > page_size = default_huge_page_size();
> > @@ -1653,7 +1704,7 @@ int main(int argc, char **argv)
> > err("failed to arm SIGALRM");
> > alarm(ALARM_INTERVAL_SECS);
> >
> > - set_test_type(argv[1]);
> > + parse_test_type_arg(argv[1]);
> >
> > nr_cpus = sysconf(_SC_NPROCESSORS_ONLN);
> > nr_pages_per_cpu = atol(argv[2]) * 1024*1024 / page_size /
> > --
> > 2.37.1.559.g78731f0fdb-goog
> >
>
> --
> Sincerely yours,
> Mike.
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