drm/i915/ttm: Failsafe migration blits

If the initial fill blit or copy blit of an object fails, the old
content of the data might be exposed and read as soon as either CPU- or
GPU PTEs are set up to point at the pages.

Intercept the blit fence with an async callback that checks the
blit fence for errors and if there are errors performs an async cpu blit
instead. If there is a failure to allocate the async dma_fence_work,
allocate it on the stack and sync wait for the blit to complete.

Add selftests that simulate gpu blit failures and failure to allocate
the async dma_fence_work.

A previous version of this pach used dma_fence_work, now that's
opencoded which adds more code but might lower the latency
somewhat in the common non-error case.

v3:
- Style fixes (Matthew Auld)
v4:
- Use "#if IS_ENABLED()" instead of #ifdef (Matthew Auld)
v5:
- Fix an issue where we, if the dependency was already signaled, might
  end up waiting for a memcpy fence that would never signal.
v6:
- Add a missing i915_ttm_memcpy_release() (Matthew Auld)
Signed-off-by: Thomas Hellström <thomas.hellstrom@linux.intel.com>
Reviewed-by: Matthew Auld <matthew.auld@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20211104110718.688420-3-thomas.hellstrom@linux.intel.com

drivers/gpu/drm/i915/gem/i915_gem_ttm_move.h

@@ -7,6 +7,8 @@
 
 #include <linux/types.h>
 
+#include "i915_selftest.h"
+
 struct ttm_buffer_object;
 struct ttm_operation_ctx;
 struct ttm_place;
@@ -18,6 +20,9 @@ struct i915_refct_sgt;
 
 int i915_ttm_move_notify(struct ttm_buffer_object *bo);
 
+I915_SELFTEST_DECLARE(void i915_ttm_migrate_set_failure_modes(bool gpu_migration,
+							      bool work_allocation));
+
 /* Internal I915 TTM declarations and definitions below. */
 
 void __i915_ttm_move(struct ttm_buffer_object *bo, bool clear,

drivers/gpu/drm/i915/gem/selftests/i915_gem_migrate.c

@@ -4,6 +4,7 @@
  */
 
 #include "gt/intel_migrate.h"
+#include "gem/i915_gem_ttm_move.h"
 
 static int igt_fill_check_buffer(struct drm_i915_gem_object *obj,
 				 bool fill)
@@ -227,13 +228,34 @@ static int igt_lmem_pages_migrate(void *arg)
 	return err;
 }
 
+static int igt_lmem_pages_failsafe_migrate(void *arg)
+{
+	int fail_gpu, fail_alloc, ret;
+
+	for (fail_gpu = 0; fail_gpu < 2; ++fail_gpu) {
+		for (fail_alloc = 0; fail_alloc < 2; ++fail_alloc) {
+			pr_info("Simulated failure modes: gpu: %d, alloc: %d\n",
+				fail_gpu, fail_alloc);
+			i915_ttm_migrate_set_failure_modes(fail_gpu,
+							   fail_alloc);
+			ret = igt_lmem_pages_migrate(arg);
+			if (ret)
+				goto out_err;
+		}
+	}
+
+out_err:
+	i915_ttm_migrate_set_failure_modes(false, false);
+	return ret;
+}
+
 int i915_gem_migrate_live_selftests(struct drm_i915_private *i915)
 {
 	static const struct i915_subtest tests[] = {
 		SUBTEST(igt_smem_create_migrate),
 		SUBTEST(igt_lmem_create_migrate),
 		SUBTEST(igt_same_create_migrate),
-		SUBTEST(igt_lmem_pages_migrate),
+		SUBTEST(igt_lmem_pages_failsafe_migrate),
 	};
 
 	if (!HAS_LMEM(i915))