Not too long ago, we realised we had issues with a rolling back a
context so far for a preemption request we considered the resubmit not
to be a rollback but a forward roll. This means we would issue a lite
restore instead of forcing a full restore, continuing execution of the
old requests rather than causing a preemption. Add a selftest to
exercise such a far rollback, such that if we were to skip the full
restore, we would execute invalid instructions in the ring and hang.
Note that while I was able to confirm that this causes us to do a
lite-restore preemption rollback (with commit e36ba817fa96 ("drm/i915/gt:
Incrementally check for rewinding") disabled), it did not trick the HW
into rolling past the old RING_TAIL. Myybe on other HW.
References: e36ba817fa96 ("drm/i915/gt: Incrementally check for rewinding")
Signed-off-by: Chris Wilson <chris@xxxxxxxxxxxxxxxxxx>
Cc: Mika Kuoppala <mika.kuoppala@xxxxxxxxxxxxxxx>
---
drivers/gpu/drm/i915/gt/selftest_lrc.c | 150 +++++++++++++++++++++++++
1 file changed, 150 insertions(+)
diff --git a/drivers/gpu/drm/i915/gt/selftest_lrc.c b/drivers/gpu/drm/i915/gt/selftest_lrc.c
index 91543494f595..3d088116a055 100644
--- a/drivers/gpu/drm/i915/gt/selftest_lrc.c
+++ b/drivers/gpu/drm/i915/gt/selftest_lrc.c
@@ -363,6 +363,155 @@ static int live_unlite_preempt(void *arg)
return live_unlite_restore(arg, I915_USER_PRIORITY(I915_PRIORITY_MAX));
}
+static int live_unlite_ring(void *arg)
+{
+ struct intel_gt *gt = arg;
+ struct intel_engine_cs *engine;
+ struct igt_spinner spin;
+ enum intel_engine_id id;
+ int err = 0;
+
+ /*
+ * Setup a preemption event that will cause almost the entire ring
+ * to be unwound, potentially fooling our intel_ring_direction()
+ * into emitting a forward lite-restore instead of the rollback.
+ */
+
+ if (igt_spinner_init(&spin, gt))
+ return -ENOMEM;
+
+ for_each_engine(engine, gt, id) {
+ struct intel_context *ce[2] = {};
+ struct i915_request *rq;
+ struct igt_live_test t;
+ int n;
+
+ if (!intel_engine_has_preemption(engine))
+ continue;
+
+ if (!intel_engine_can_store_dword(engine))
+ continue;
+
+ if (igt_live_test_begin(&t, gt->i915, __func__, engine->name)) {
+ err = -EIO;
+ break;
+ }
+ engine_heartbeat_disable(engine);
+
+ for (n = 0; n < ARRAY_SIZE(ce); n++) {
+ struct intel_context *tmp;
+
+ tmp = intel_context_create(engine);
+ if (IS_ERR(tmp)) {
+ err = PTR_ERR(tmp);
+ goto err_ce;
+ }
+
+ err = intel_context_pin(tmp);
+ if (err) {
+ intel_context_put(tmp);
+ goto err_ce;
+ }
+
+ memset32(tmp->ring->vaddr,
+ 0xdeadbeef, /* trigger a hang if executed */
+ tmp->ring->vma->size / sizeof(u32));
+
+ ce[n] = tmp;
+ }
+
+ rq = igt_spinner_create_request(&spin, ce[0], MI_ARB_CHECK);
+ if (IS_ERR(rq)) {
+ err = PTR_ERR(rq);
+ goto err_ce;
+ }
+
+ i915_request_get(rq);
+ rq->sched.attr.priority = I915_PRIORITY_BARRIER;
+ i915_request_add(rq);
+
+ if (!igt_wait_for_spinner(&spin, rq)) {
+ intel_gt_set_wedged(gt);
+ i915_request_put(rq);
+ err = -ETIME;
+ goto err_ce;
+ }
+
+ /* Fill the ring, until we will cause a wrap */
+ n = 0;
+ while (intel_ring_direction(ce[0]->ring,
+ rq->wa_tail,
+ ce[0]->ring->tail) <= 0) {
+ struct i915_request *tmp;
+
+ tmp = intel_context_create_request(ce[0]);
+ if (IS_ERR(tmp)) {
+ err = PTR_ERR(tmp);
+ i915_request_put(rq);
+ goto err_ce;
+ }
+
+ i915_request_add(tmp);
+ intel_engine_flush_submission(engine);
+ n++;
+ }
+ intel_engine_flush_submission(engine);
+ pr_debug("%s: Filled ring with %d nop tails {size:%x, tail:%x, emit:%x, rq.tail:%x}\n",
+ engine->name, n,
+ ce[0]->ring->size,
+ ce[0]->ring->tail,
+ ce[0]->ring->emit,
+ rq->tail);
+ GEM_BUG_ON(intel_ring_direction(ce[0]->ring,
+ rq->tail,
+ ce[0]->ring->tail) <= 0);
+ i915_request_put(rq);
+
+ /* Create a second request to preempt the first ring */
+ rq = intel_context_create_request(ce[1]);
+ if (IS_ERR(rq)) {
+ err = PTR_ERR(rq);
+ goto err_ce;
+ }
+
+ rq->sched.attr.priority = I915_PRIORITY_BARRIER;
+ i915_request_get(rq);
+ i915_request_add(rq);
+
+ err = wait_for_submit(engine, rq, HZ / 2);
+ i915_request_put(rq);
+ if (err) {
+ pr_err("%s: preemption request was not submited\n",
+ engine->name);
+ err = -ETIME;
+ }
+
+ pr_debug("%s: ring[0]:{ tail:%x, emit:%x }, ring[1]:{ tail:%x, emit:%x }\n",
+ engine->name,
+ ce[0]->ring->tail, ce[0]->ring->emit,
+ ce[1]->ring->tail, ce[1]->ring->emit);
+
+err_ce:
+ intel_engine_flush_submission(engine);
+ igt_spinner_end(&spin);
+ for (n = 0; n < ARRAY_SIZE(ce); n++) {
+ if (IS_ERR_OR_NULL(ce[n]))
+ break;
+
+ intel_context_unpin(ce[n]);
+ intel_context_put(ce[n]);
+ }
+ engine_heartbeat_enable(engine);
+ if (igt_live_test_end(&t))
+ err = -EIO;
+ if (err)
+ break;
+ }
+
+ igt_spinner_fini(&spin);
+ return err;
+}
+
static int live_pin_rewind(void *arg)
{
struct intel_gt *gt = arg;
@@ -4374,6 +4523,7 @@ int intel_execlists_live_selftests(struct drm_i915_private *i915)
SUBTEST(live_sanitycheck),
SUBTEST(live_unlite_switch),
SUBTEST(live_unlite_preempt),
+ SUBTEST(live_unlite_ring),
SUBTEST(live_pin_rewind),
SUBTEST(live_hold_reset),
SUBTEST(live_error_interrupt),
--
2.20.1
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