Re: [PATCH v2 3/6] userfaultfd: selftests: modify selftest to use /dev/userfaultfd

From: Shuah Khan <skhan@linuxfoundation.org>
To: Axel Rasmussen <axelrasmussen@google.com>,
	Alexander Viro <viro@zeniv.linux.org.uk>,
	Andrew Morton <akpm@linux-foundation.org>,
	Charan Teja Reddy <charante@codeaurora.org>,
	Dave Hansen <dave.hansen@linux.intel.com>,
	"Dmitry V . Levin" <ldv@altlinux.org>,
	Gleb Fotengauer-Malinovskiy <glebfm@altlinux.org>,
	Hugh Dickins <hughd@google.com>, Jan Kara <jack@suse.cz>,
	Jonathan Corbet <corbet@lwn.net>,
	Mel Gorman <mgorman@techsingularity.net>,
	Mike Kravetz <mike.kravetz@oracle.com>,
	Mike Rapoport <rppt@kernel.org>, Nadav Amit <namit@vmware.com>,
	Peter Xu <peterx@redhat.com>, Shuah Khan <shuah@kernel.org>,
	Suren Baghdasaryan <surenb@google.com>,
	Vlastimil Babka <vbabka@suse.cz>, zhangyi <yi.zhang@huawei.com>
Cc: linux-doc@vger.kernel.org, linux-fsdevel@vger.kernel.org,
	linux-kernel@vger.kernel.org, linux-mm@kvack.org,
	linux-kselftest@vger.kernel.org,
	Shuah Khan <skhan@linuxfoundation.org>
Subject: Re: [PATCH v2 3/6] userfaultfd: selftests: modify selftest to use /dev/userfaultfd
Date: Tue, 26 Apr 2022 10:16:18 -0600	[thread overview]
Message-ID: <a6f7ff80-ea77-75d0-2454-99d14f164708@linuxfoundation.org> (raw)
In-Reply-To: <20220422212945.2227722-4-axelrasmussen@google.com>

On 4/22/22 3:29 PM, 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.
> 
> Signed-off-by: Axel Rasmussen <axelrasmussen@google.com>
> ---
>   tools/testing/selftests/vm/userfaultfd.c | 31 ++++++++++++++++++++++--
>   1 file changed, 29 insertions(+), 2 deletions(-)
> 
> diff --git a/tools/testing/selftests/vm/userfaultfd.c b/tools/testing/selftests/vm/userfaultfd.c
> index 92a4516f8f0d..12ae742a9981 100644
> --- a/tools/testing/selftests/vm/userfaultfd.c
> +++ b/tools/testing/selftests/vm/userfaultfd.c
> @@ -77,6 +77,9 @@ static int bounces;
>   #define TEST_SHMEM	3
>   static int test_type;
>   
> +/* 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;
> @@ -383,13 +386,31 @@ static void assert_expected_ioctls_present(uint64_t mode, uint64_t ioctls)
>   	}
>   }
>   
> +static void __userfaultfd_open_dev(void)
> +{
> +	int fd;
> +
> +	uffd = -1;
> +	fd = open("/dev/userfaultfd", O_RDWR | O_CLOEXEC);
> +	if (fd < 0)
> +		return;
> +
> +	uffd = ioctl(fd, USERFAULTFD_IOC_NEW,
> +		     O_CLOEXEC | O_NONBLOCK | UFFD_USER_MODE_ONLY);
> +	close(fd);
> +}
> +
>   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)
> +		__userfaultfd_open_dev();
> +	else
> +		uffd = syscall(__NR_userfaultfd,
> +			       O_CLOEXEC | O_NONBLOCK | UFFD_USER_MODE_ONLY);
>   	if (uffd < 0)
> -		err("userfaultfd syscall not available in this kernel");
> +		err("creating userfaultfd failed");

This isn't an error as in test failure. This will be a skip because of
unmet dependencies. Also if this test requires root access, please check
for that and make that a skip as well.

>   	uffd_flags = fcntl(uffd, F_GETFD, NULL);
>   
>   	uffdio_api.api = UFFD_API;
> @@ -1698,6 +1719,12 @@ int main(int argc, char **argv)
>   	}
>   	printf("nr_pages: %lu, nr_pages_per_cpu: %lu\n",
>   	       nr_pages, nr_pages_per_cpu);
> +
> +	test_dev_userfaultfd = false;
> +	if (userfaultfd_stress())
> +		return 1;
> +
> +	test_dev_userfaultfd = true;
>   	return userfaultfd_stress();
>   }
>   
> 

thanks,
-- Shuah