[igt-dev] [RFC PATCH i-g-t v2 2/2] tests/gem_userptr_blits: Exercise mmap-offset mapping to userptr

[Janusz Krzysztofik]

Currently unavoidable lockedp loop related to userptr MMU notifier
exists in the i915 driver.  For that reason, attempts to set up a
mmap-offset (or mmap-gtt) mapping to a userptr object may be now
preventively rejected by the driver.

A test should exists which checks for that.  Would a mapping attempt
succeed, the test should trigger the MMU notifier in a way that is
proven to result in the lockdep slpat.

As that exercise is strictly userptr related, it has been decided to
add it as a new subtest to gem_userptr_blits.  The new subtest examines
userptr interaction with every supported mmap-offset type mapping on
top of it.

v2: Move the subtest from gem_mmap_offset to gem_userptr_blits,
  - use dynamic subtests (Chris),
  - don't FAIL but SKIP on mmap-offset attempt failure (Chris),
  - on success, try to anger lockdep (Chris).

Suggested-by: Chris Wilson <chris at chris-wilson.co.uk
Signed-off-by: Janusz Krzysztofik <janusz.krzysztofik at linux.intel.com>
Cc: Matthew Auld <matthew.auld at intel.com>
---
In order to be able to prove the proposed method of angering lockdep
actually works,  I'm going to submit a kernel patch that reverts commit
f6c26b555e14 ("drm/i915: Never allow userptr into the new mapping
types") to be tested on Trybot together with this one, so at least
non-GTT mmap-offset attempts succeed and the MMU notifier is triggered.

Thanks,
Janusz

 tests/i915/gem_userptr_blits.c | 42 ++++++++++++++++++++++++++++++++++
 1 file changed, 42 insertions(+)

diff --git a/tests/i915/gem_userptr_blits.c b/tests/i915/gem_userptr_blits.c
index fcad374ef..5f716a3ea 100644
--- a/tests/i915/gem_userptr_blits.c
+++ b/tests/i915/gem_userptr_blits.c
@@ -797,6 +797,42 @@ static int test_map_fixed_invalidate(int fd, uint32_t flags)
 	return 0;
 }
 
+static void test_mmap_offset_invalidate(int fd, const struct mmap_offset *t)
+{
+	void *ptr, *map;
+	uint32_t handle;
+
+	/* check if mmap_offset type is supported by hardware, skip if not */
+	handle = gem_create(fd, PAGE_SIZE);
+	map = __gem_mmap_offset(fd, handle, 0, PAGE_SIZE,
+				PROT_READ | PROT_WRITE, t->type);
+	igt_require_f(map,
+		      "HW & kernel support for mmap_offset(%s)\n", t->name);
+	munmap(map, PAGE_SIZE);
+	gem_close(fd, handle);
+
+	/* create userptr object */
+	igt_assert_eq(posix_memalign(&ptr, PAGE_SIZE, PAGE_SIZE), 0);
+	gem_userptr(fd, ptr, PAGE_SIZE, 0, userptr_flags, &handle);
+
+	/* set up mmap-offset mapping on top of the object, skip if refused */
+	map = __gem_mmap_offset(fd, handle, 0, PAGE_SIZE,
+				PROT_READ | PROT_WRITE, t->type);
+	igt_skip_on_f(!map && errno == -ENODEV,
+		      "lockdep loop preventive failure possibly occurred\n");
+	igt_assert(map);
+
+	/* set object pages in order to activate MMU notifier for it */
+	gem_set_domain(fd, handle, t->domain, t->domain);
+
+	/* trigger the notifier */
+	munmap(ptr, PAGE_SIZE);
+
+	/* cleanup */
+	munmap(map, PAGE_SIZE);
+	gem_close(fd, handle);
+}
+
 static int test_forbidden_ops(int fd)
 {
 	struct drm_i915_gem_pread gem_pread;
@@ -2170,6 +2206,12 @@ igt_main_args("c:", NULL, help_str, opt_handler, NULL)
 			}
 		}
 
+		igt_describe("Invalidate pages of userptr with mmap-offset on top");
+		igt_subtest_with_dynamic("mmap-offset-invalidate")
+			for_each_mmap_offset_type(fd, t)
+				igt_dynamic_f("%s", t->name)
+					test_mmap_offset_invalidate(fd, t);
+
 		igt_subtest("coherency-sync")
 			test_coherency(fd, count);
 
-- 
2.21.0