linux-kernel - Re: [PATCH 14/29] selftests/mm: uffd

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Date:   Fri, 7 Apr 2023 14:08:54 +0300
From:   Mike Rapoport <rppt@...ux.ibm.com>
To:     Peter Xu <peterx@...hat.com>
Cc:     linux-mm@...ck.org, linux-kernel@...r.kernel.org,
        Andrea Arcangeli <aarcange@...hat.com>,
        David Hildenbrand <david@...hat.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Nadav Amit <nadav.amit@...il.com>,
        Mike Kravetz <mike.kravetz@...cle.com>,
        Axel Rasmussen <axelrasmussen@...gle.com>,
        Leonardo Bras Soares Passos <lsoaresp@...hat.com>,
        Mike Rapoport <rppt@...ux.vnet.ibm.com>
Subject: Re: [PATCH 14/29] selftests/mm: uffd_[un]register()

On Thu, Mar 30, 2023 at 12:07:47PM -0400, Peter Xu wrote:
> Add two helpers to register/unregister to an uffd.  Use them to drop
> duplicate codes.
> 
> This patch also drops assert_expected_ioctls_present() and
> get_expected_ioctls().  Reasons:
> 
>   - It'll need a lot of effort to pass test_type==HUGETLB into it from the
>   upper, so it's the simplest way to get rid of another global var
> 
>   - The ioctls returned in UFFDIO_REGISTER is hardly useful at all, because
>   any app can already detect kernel support on any ioctl via its
>   corresponding UFFD_FEATURE_*.  The check here is for sanity mostly but
>   it's probably destined no user app will even use it.
> 
>   - It's not friendly to one future goal of uffd to run on old kernels, the
>   problem is get_expected_ioctls() compiles against UFFD_API_RANGE_IOCTLS,
>   which is a value that can change depending on where the test is compiled,
>   rather than reflecting what the kernel underneath has.  It means it'll
>   report false negatives on old kernels so it's against our will.
> 
> So let's make our live easier.
> 
> Signed-off-by: Peter Xu <peterx@...hat.com>
> ---
>  tools/testing/selftests/mm/hugepage-mremap.c  |  7 +-
>  .../selftests/mm/ksm_functional_tests.c       |  6 +-
>  tools/testing/selftests/mm/uffd-common.c      | 28 +------
>  tools/testing/selftests/mm/uffd-common.h      |  2 -
>  tools/testing/selftests/mm/uffd-stress.c      | 83 +++++--------------
>  tools/testing/selftests/mm/vm_util.c          | 37 +++++++++
>  tools/testing/selftests/mm/vm_util.h          |  7 ++
>  7 files changed, 66 insertions(+), 104 deletions(-)
> 
> diff --git a/tools/testing/selftests/mm/hugepage-mremap.c b/tools/testing/selftests/mm/hugepage-mremap.c
> index e53b5eaa8fce..2084692fe1c4 100644
> --- a/tools/testing/selftests/mm/hugepage-mremap.c
> +++ b/tools/testing/selftests/mm/hugepage-mremap.c
> @@ -60,7 +60,6 @@ static void register_region_with_uffd(char *addr, size_t len)
>  {
>  	long uffd; /* userfaultfd file descriptor */
>  	struct uffdio_api uffdio_api;
> -	struct uffdio_register uffdio_register;
> 
>  	/* Create and enable userfaultfd object. */
> 
> @@ -96,11 +95,7 @@ static void register_region_with_uffd(char *addr, size_t len)
>  	 * handling by the userfaultfd object. In mode, we request to track
>  	 * missing pages (i.e., pages that have not yet been faulted in).
>  	 */
> -
> -	uffdio_register.range.start = (unsigned long)addr;
> -	uffdio_register.range.len = len;
> -	uffdio_register.mode = UFFDIO_REGISTER_MODE_MISSING;
> -	if (ioctl(uffd, UFFDIO_REGISTER, &uffdio_register) == -1) {
> +	if (uffd_register(uffd, addr, len, true, false, false)) {

I'd replace booleans with a bit flags as it easier to read.
Other than that LGTM.

>  		perror("ioctl-UFFDIO_REGISTER");
>  		exit(1);
>  	}

-- 
Sincerely yours,
Mike.