Messages in this thread Patch in this message | | | Date | Mon, 29 Apr 2024 09:28:15 +0200 | Subject | Re: [PATCH 2/2] mm/selftests: Don't prefault in gup_longterm tests | From | David Hildenbrand <> |
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On 28.04.24 21:01, Peter Xu wrote: > Prefault, especially with RW, makes the GUP test too easy, and may not yet > reach the core of the test. > > For example, R/O longterm pins will just hit, pte_write()==true for > whatever cases, the unsharing logic won't be ever tested. > > This patch remove the prefault. This tortures more code paths at least to > cover the unshare care for R/O longterm pins, in which case the first R/O > GUP attempt will fault in the page R/O first, then the 2nd will go through > the unshare path, checking whether an unshare is needed. > > Cc: David Hildenbrand <david@redhat.com> > Signed-off-by: Peter Xu <peterx@redhat.com> > --- > tools/testing/selftests/mm/gup_longterm.c | 12 +++++++++--- > 1 file changed, 9 insertions(+), 3 deletions(-) > > diff --git a/tools/testing/selftests/mm/gup_longterm.c b/tools/testing/selftests/mm/gup_longterm.c > index ad168d35b23b..488e32186246 100644 > --- a/tools/testing/selftests/mm/gup_longterm.c > +++ b/tools/testing/selftests/mm/gup_longterm.c > @@ -119,10 +119,16 @@ static void do_test(int fd, size_t size, enum test_type type, bool shared) > } > > /* > - * Fault in the page writable such that GUP-fast can eventually pin > - * it immediately. > + * Explicitly avoid pre-faulting in the page, this can help testing > + * more code paths. > + * > + * Take example of an upcoming R/O pin test, if we RW prefault the > + * page, such pin will directly skip R/O unsharing and the longterm > + * pin will success mostly always. When not prefaulted, R/O > + * longterm pin will first fault in a RO page, then the 2nd round > + * it'll go via the unshare check. Otherwise those paths aren't > + * covered. > */ This will mean that GUP-fast never succeeds, which removes quite some testing coverage for most other tests here.
Note that the main motivation of this test was to test gup_fast_folio_allowed(), where we had issues with GUP-fast during development.
Would the following also get the job done?
diff --git a/tools/testing/selftests/mm/gup_longterm.c b/tools/testing/selftests/mm/gup_longterm.c index ad168d35b23b7..e917a7c58d571 100644 --- a/tools/testing/selftests/mm/gup_longterm.c +++ b/tools/testing/selftests/mm/gup_longterm.c @@ -92,7 +92,7 @@ static void do_test(int fd, size_t size, enum test_type type, bool shared) { __fsword_t fs_type = get_fs_type(fd); bool should_work; - char *mem; + char tmp, *mem; int ret; if (ftruncate(fd, size)) { @@ -119,10 +119,19 @@ static void do_test(int fd, size_t size, enum test_type type, bool shared) } /* - * Fault in the page writable such that GUP-fast can eventually pin - * it immediately. + * Fault in the page such that GUP-fast might be able to pin it + * immediately. To cover more cases, don't fault in pages writable when + * R/O pinning. */ - memset(mem, 0, size); + switch (type) { + case TEST_TYPE_RO: + case TEST_TYPE_RO_FAST: + tmp = *mem; + asm volatile("" : "+r" (tmp)); + break; + default: + memset(mem, 0, size); + }; switch (type) { case TEST_TYPE_RO: -- 2.44.0
-- Cheers,
David / dhildenb
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