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

Peter Xu
2019-02-26T07:52:48Z

On Tue, Feb 26, 2019 at 08:58:36AM +0200, Mike Rapoport wrote:
> 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@redhat.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?

Yes it didn't fail the test case probably because the test case only
registers the shmem region with UFFDIO_REGISTER_MODE_MISSING, and for
now we'll simply blindly return the _UFFDIO_WRITEPROTECT capability if
the register ioctl succeeded. However it'll still fail the
UFFDIO_REGISTER ioctl directly if someone requests with
UFFDIO_REGISTER_MODE_WP mode upon shmem.

So maybe I should explicitly remove the _UFFDIO_WRITEPROTECT bit in
userfaultfd_register() if I detected any non-anonymous regions? Then
here I will revert to ANON_EXPECTED_IOCTLS for shmem_uffd_test_ops in
the tests.

>
> > .allocate_area = shmem_allocate_area,
> > .release_pages = shmem_release_pages,
> > .alias_mapping = noop_alias_mapping,
>
> ...
>
> --
> Sincerely yours,
> Mike.
>

Regards,

--
Peter Xu