linux-kernel - Re: [PATCH 5.13 191/223] selftest: use mmap instead of posix

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Date:   Thu, 29 Jul 2021 10:58:11 -0700
From:   Peter Collingbourne <pcc@...gle.com>
To:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>
Cc:     linux-kernel@...r.kernel.org, stable@...r.kernel.org,
        Lokesh Gidra <lokeshgidra@...gle.com>,
        Catalin Marinas <catalin.marinas@....com>,
        Vincenzo Frascino <vincenzo.frascino@....com>,
        Dave Martin <Dave.Martin@....com>,
        Will Deacon <will@...nel.org>,
        Andrea Arcangeli <aarcange@...hat.com>,
        Alistair Delva <adelva@...gle.com>,
        William McVicker <willmcvicker@...gle.com>,
        Evgenii Stepanov <eugenis@...gle.com>,
        Mitch Phillips <mitchp@...gle.com>,
        Andrey Konovalov <andreyknvl@...il.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        donnyxia@...gle.com
Subject: Re: [PATCH 5.13 191/223] selftest: use mmap instead of posix_memalign
 to allocate memory

On Mon, Jul 26, 2021 at 9:16 AM Greg Kroah-Hartman
<gregkh@...uxfoundation.org> wrote:
>
> From: Peter Collingbourne <pcc@...gle.com>
>
> commit 0db282ba2c12c1515d490d14a1ff696643ab0f1b upstream.
>
> This test passes pointers obtained from anon_allocate_area to the
> userfaultfd and mremap APIs.  This causes a problem if the system
> allocator returns tagged pointers because with the tagged address ABI
> the kernel rejects tagged addresses passed to these APIs, which would
> end up causing the test to fail.  To make this test compatible with such
> system allocators, stop using the system allocator to allocate memory in
> anon_allocate_area, and instead just use mmap.
>
> Link: https://lkml.kernel.org/r/20210714195437.118982-3-pcc@google.com
> Link: https://linux-review.googlesource.com/id/Icac91064fcd923f77a83e8e133f8631c5b8fc241
> Fixes: c47174fc362a ("userfaultfd: selftest")
> Co-developed-by: Lokesh Gidra <lokeshgidra@...gle.com>
> Signed-off-by: Lokesh Gidra <lokeshgidra@...gle.com>
> Signed-off-by: Peter Collingbourne <pcc@...gle.com>
> Reviewed-by: Catalin Marinas <catalin.marinas@....com>
> Cc: Vincenzo Frascino <vincenzo.frascino@....com>
> Cc: Dave Martin <Dave.Martin@....com>
> Cc: Will Deacon <will@...nel.org>
> Cc: Andrea Arcangeli <aarcange@...hat.com>
> Cc: Alistair Delva <adelva@...gle.com>
> Cc: William McVicker <willmcvicker@...gle.com>
> Cc: Evgenii Stepanov <eugenis@...gle.com>
> Cc: Mitch Phillips <mitchp@...gle.com>
> Cc: Andrey Konovalov <andreyknvl@...il.com>
> Cc: <stable@...r.kernel.org>    [5.4]
> Signed-off-by: Andrew Morton <akpm@...ux-foundation.org>
> Signed-off-by: Linus Torvalds <torvalds@...ux-foundation.org>
> Signed-off-by: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
> ---
>  tools/testing/selftests/vm/userfaultfd.c |    6 ++++--
>  1 file changed, 4 insertions(+), 2 deletions(-)
>
> --- a/tools/testing/selftests/vm/userfaultfd.c
> +++ b/tools/testing/selftests/vm/userfaultfd.c
> @@ -197,8 +197,10 @@ static int anon_release_pages(char *rel_
>
>  static void anon_allocate_area(void **alloc_area)
>  {
> -       if (posix_memalign(alloc_area, page_size, nr_pages * page_size)) {
> -               fprintf(stderr, "out of memory\n");
> +       *alloc_area = mmap(NULL, nr_pages * page_size, PROT_READ | PROT_WRITE,
> +                          MAP_ANONYMOUS | MAP_PRIVATE, -1, 0);
> +       if (*alloc_area == MAP_FAILED)

Hi Greg,

It looks like your backport of this patch (and the backports to stable
kernels) are missing a left brace here.

Peter

> +               fprintf(stderr, "mmap of anonymous memory failed");
>                 *alloc_area = NULL;
>         }
>  }
>
>