linux-kernel - Re: [PATCH v3 3/6] userfaultfd: selftests: modify selftest to use /dev/userfaultfd

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Message-ID: <YqjgkKGrS89kiZWS@xz-m1.local>
Date:   Tue, 14 Jun 2022 15:25:04 -0400
From:   Peter Xu <peterx@...hat.com>
To:     Axel Rasmussen <axelrasmussen@...gle.com>
Cc:     Alexander Viro <viro@...iv.linux.org.uk>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Charan Teja Reddy <charante@...eaurora.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>,
        Mike Rapoport <rppt@...nel.org>, Nadav Amit <namit@...are.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@...r.kernel.org, linux-kernel@...r.kernel.org,
        linux-mm@...ck.org, linux-kselftest@...r.kernel.org
Subject: Re: [PATCH v3 3/6] userfaultfd: selftests: modify selftest to use
 /dev/userfaultfd

On Wed, Jun 01, 2022 at 02:09:48PM -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.
> 
> Signed-off-by: Axel Rasmussen <axelrasmussen@...gle.com>
> ---
>  tools/testing/selftests/vm/userfaultfd.c | 37 +++++++++++++++++++++---
>  1 file changed, 33 insertions(+), 4 deletions(-)
> 
> diff --git a/tools/testing/selftests/vm/userfaultfd.c b/tools/testing/selftests/vm/userfaultfd.c
> index 0bdfc1955229..1badb5d31bf9 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;
> @@ -154,12 +157,14 @@ 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 +388,31 @@ 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();

I can understand uffd is a global var, but still AFAICT that's trivially
easy to do the return to match the syscall case..

                uffd = __userfaultfd_open_dev();

And since at it, it'll be great to make a macro:

#define  UFFD_FLAGS  (O_CLOEXEC | O_NONBLOCK | UFFD_USER_MODE_ONLY)

Thanks,

> +	else
> +		uffd = syscall(__NR_userfaultfd,
> +			       O_CLOEXEC | O_NONBLOCK | UFFD_USER_MODE_ONLY);
>  	if (uffd < 0)
> -		err("userfaultfd syscall not available in this kernel");
> +		errexit(KSFT_SKIP, "creating userfaultfd failed");
>  	uffd_flags = fcntl(uffd, F_GETFD, NULL);
>  
>  	uffdio_api.api = UFFD_API;
> @@ -1691,6 +1714,12 @@ 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();
>  }
>  
> -- 
> 2.36.1.255.ge46751e96f-goog
> 

-- 
Peter Xu