linux-kernel - Re: [PATCH v2 26/26] userfaultfd: selftests: add write-protect test

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Date:   Tue, 26 Feb 2019 08:58:36 +0200
From:   Mike Rapoport <rppt@...ux.ibm.com>
To:     Peter Xu <peterx@...hat.com>
Cc:     linux-mm@...ck.org, linux-kernel@...r.kernel.org,
        David Hildenbrand <david@...hat.com>,
        Hugh Dickins <hughd@...gle.com>,
        Maya Gokhale <gokhale2@...l.gov>,
        Jerome Glisse <jglisse@...hat.com>,
        Pavel Emelyanov <xemul@...tuozzo.com>,
        Johannes Weiner <hannes@...xchg.org>,
        Martin Cracauer <cracauer@...s.org>, Shaohua Li <shli@...com>,
        Marty McFadden <mcfadden8@...l.gov>,
        Andrea Arcangeli <aarcange@...hat.com>,
        Mike Kravetz <mike.kravetz@...cle.com>,
        Denis Plotnikov <dplotnikov@...tuozzo.com>,
        Mike Rapoport <rppt@...ux.vnet.ibm.com>,
        Mel Gorman <mgorman@...e.de>,
        "Kirill A . Shutemov" <kirill@...temov.name>,
        "Dr . David Alan Gilbert" <dgilbert@...hat.com>
Subject: Re: [PATCH v2 26/26] userfaultfd: selftests: add write-protect test

On Tue, Feb 12, 2019 at 10:56:32AM +0800, Peter Xu wrote:
> This patch adds uffd tests for write protection.
> 
> Instead of introducing new tests for it, let's simply squashing uffd-wp
> tests into existing uffd-missing test cases.  Changes are:
> 
> (1) Bouncing tests
> 
>   We do the write-protection in two ways during the bouncing test:
> 
>   - By using UFFDIO_COPY_MODE_WP when resolving MISSING pages: then
>     we'll make sure for each bounce process every single page will be
>     at least fault twice: once for MISSING, once for WP.
> 
>   - By direct call UFFDIO_WRITEPROTECT on existing faulted memories:
>     To further torture the explicit page protection procedures of
>     uffd-wp, we split each bounce procedure into two halves (in the
>     background thread): the first half will be MISSING+WP for each
>     page as explained above.  After the first half, we write protect
>     the faulted region in the background thread to make sure at least
>     half of the pages will be write protected again which is the first
>     half to test the new UFFDIO_WRITEPROTECT call.  Then we continue
>     with the 2nd half, which will contain both MISSING and WP faulting
>     tests for the 2nd half and WP-only faults from the 1st half.
> 
> (2) Event/Signal test
> 
>   Mostly previous tests but will do MISSING+WP for each page.  For
>   sigbus-mode test we'll need to provide standalone path to handle the
>   write protection faults.
> 
> For all tests, do statistics as well for uffd-wp pages.
> 
> Signed-off-by: Peter Xu <peterx@...hat.com>
> ---
>  tools/testing/selftests/vm/userfaultfd.c | 154 ++++++++++++++++++-----
>  1 file changed, 126 insertions(+), 28 deletions(-)
> 
> diff --git a/tools/testing/selftests/vm/userfaultfd.c b/tools/testing/selftests/vm/userfaultfd.c
> index e5d12c209e09..57b5ac02080a 100644
> --- a/tools/testing/selftests/vm/userfaultfd.c
> +++ b/tools/testing/selftests/vm/userfaultfd.c
> @@ -56,6 +56,7 @@
>  #include <linux/userfaultfd.h>
>  #include <setjmp.h>
>  #include <stdbool.h>
> +#include <assert.h>
> 
>  #include "../kselftest.h"
> 
> @@ -78,6 +79,8 @@ static int test_type;
>  #define ALARM_INTERVAL_SECS 10
>  static volatile bool test_uffdio_copy_eexist = true;
>  static volatile bool test_uffdio_zeropage_eexist = true;
> +/* Whether to test uffd write-protection */
> +static bool test_uffdio_wp = false;
> 
>  static bool map_shared;
>  static int huge_fd;
> @@ -92,6 +95,7 @@ pthread_attr_t attr;
>  struct uffd_stats {
>  	int cpu;
>  	unsigned long missing_faults;
> +	unsigned long wp_faults;
>  };
> 
>  /* pthread_mutex_t starts at page offset 0 */
> @@ -141,9 +145,29 @@ static void uffd_stats_reset(struct uffd_stats *uffd_stats,
>  	for (i = 0; i < n_cpus; i++) {
>  		uffd_stats[i].cpu = i;
>  		uffd_stats[i].missing_faults = 0;
> +		uffd_stats[i].wp_faults = 0;
>  	}
>  }
> 
> +static void uffd_stats_report(struct uffd_stats *stats, int n_cpus)
> +{
> +	int i;
> +	unsigned long long miss_total = 0, wp_total = 0;
> +
> +	for (i = 0; i < n_cpus; i++) {
> +		miss_total += stats[i].missing_faults;
> +		wp_total += stats[i].wp_faults;
> +	}
> +
> +	printf("userfaults: %llu missing (", miss_total);
> +	for (i = 0; i < n_cpus; i++)
> +		printf("%lu+", stats[i].missing_faults);
> +	printf("\b), %llu wp (", wp_total);
> +	for (i = 0; i < n_cpus; i++)
> +		printf("%lu+", stats[i].wp_faults);
> +	printf("\b)\n");
> +}
> +
>  static int anon_release_pages(char *rel_area)
>  {
>  	int ret = 0;
> @@ -264,19 +288,15 @@ struct uffd_test_ops {
>  	void (*alias_mapping)(__u64 *start, size_t len, unsigned long offset);
>  };
> 
> -#define ANON_EXPECTED_IOCTLS		((1 << _UFFDIO_WAKE) | \
> -					 (1 << _UFFDIO_COPY) | \
> -					 (1 << _UFFDIO_ZEROPAGE))
> -
>  static struct uffd_test_ops anon_uffd_test_ops = {
> -	.expected_ioctls = ANON_EXPECTED_IOCTLS,
> +	.expected_ioctls = UFFD_API_RANGE_IOCTLS,
>  	.allocate_area	= anon_allocate_area,
>  	.release_pages	= anon_release_pages,
>  	.alias_mapping = noop_alias_mapping,
>  };
> 
>  static struct uffd_test_ops shmem_uffd_test_ops = {
> -	.expected_ioctls = ANON_EXPECTED_IOCTLS,
> +	.expected_ioctls = UFFD_API_RANGE_IOCTLS,

Isn't UFFD_API_RANGE_IOCTLS includes UFFDIO_WP which is not supported for
shmem?

>  	.allocate_area	= shmem_allocate_area,
>  	.release_pages	= shmem_release_pages,
>  	.alias_mapping = noop_alias_mapping,

...

-- 
Sincerely yours,
Mike.