[Intel-gfx] [PATCH v8 09/15] drm/ttm: Document and optimize ttm_bo_pipeline_gutting()

Thomas Hellström
2021-05-31T17:23:13Z

If the bo is idle when calling ttm_bo_pipeline_gutting(), we unnecessarily
create a ghost object and push it out to delayed destroy.
Fix this by adding a path for idle, and document the function.

Also avoid having the bo end up in a bad state vulnerable to user-space
triggered kernel BUGs if the call to ttm_tt_create() fails.

Finally reuse ttm_bo_pipeline_gutting() in ttm_bo_evict().

Cc: Christian König <christian.koenig@amd.com>
Signed-off-by: Thomas Hellström <thomas.hellstrom@linux.intel.com>
Reviewed-by: Christian König <christian.koenig@amd.com>
---
v4:
- Clarify why we mark bo for clearing after ttm_bo_pipeline_gutting()
(Reported by Matthew Auld)
v5:
- Make ttm_tt_mark_for_clear() inline (Suggested by Christian König)
---
drivers/gpu/drm/ttm/ttm_bo.c | 20 +++++------
drivers/gpu/drm/ttm/ttm_bo_util.c | 55 ++++++++++++++++++++++++++++---
include/drm/ttm/ttm_tt.h | 13 ++++++++
3 files changed, 74 insertions(+), 14 deletions(-)

diff --git a/drivers/gpu/drm/ttm/ttm_bo.c b/drivers/gpu/drm/ttm/ttm_bo.c
index 51a94fd63bd7..be0406466460 100644
--- a/drivers/gpu/drm/ttm/ttm_bo.c
+++ b/drivers/gpu/drm/ttm/ttm_bo.c
@@ -501,10 +501,15 @@ static int ttm_bo_evict(struct ttm_buffer_object *bo,
bdev->funcs->evict_flags(bo, &placement);

if (!placement.num_placement && !placement.num_busy_placement) {
- ttm_bo_wait(bo, false, false);
+ ret = ttm_bo_wait(bo, true, false);
+ if (ret)
+ return ret;

- ttm_bo_cleanup_memtype_use(bo);
- return ttm_tt_create(bo, false);
+ /*
+ * Since we've already synced, this frees backing store
+ * immediately.
+ */
+ return ttm_bo_pipeline_gutting(bo);
}

ret = ttm_bo_mem_space(bo, &placement, &evict_mem, ctx);
@@ -976,13 +981,8 @@ int ttm_bo_validate(struct ttm_buffer_object *bo,
/*
* Remove the backing store if no placement is given.
*/
- if (!placement->num_placement && !placement->num_busy_placement) {
- ret = ttm_bo_pipeline_gutting(bo);
- if (ret)
- return ret;
-
- return ttm_tt_create(bo, false);
- }
+ if (!placement->num_placement && !placement->num_busy_placement)
+ return ttm_bo_pipeline_gutting(bo);

/*
* Check whether we need to move buffer.
diff --git a/drivers/gpu/drm/ttm/ttm_bo_util.c b/drivers/gpu/drm/ttm/ttm_bo_util.c
index 30bafac416a5..d0db63a7f00c 100644
--- a/drivers/gpu/drm/ttm/ttm_bo_util.c
+++ b/drivers/gpu/drm/ttm/ttm_bo_util.c
@@ -565,26 +565,73 @@ int ttm_bo_move_accel_cleanup(struct ttm_buffer_object *bo,
}
EXPORT_SYMBOL(ttm_bo_move_accel_cleanup);

+/**
+ * ttm_bo_pipeline_gutting - purge the contents of a bo
+ * @bo: The buffer object
+ *
+ * Purge the contents of a bo, async if the bo is not idle.
+ * After a successful call, the bo is left unpopulated in
+ * system placement. The function may wait uninterruptible
+ * for idle on OOM.
+ *
+ * Return: 0 if successful, negative error code on failure.
+ */
int ttm_bo_pipeline_gutting(struct ttm_buffer_object *bo)
{
static const struct ttm_place sys_mem = { .mem_type = TTM_PL_SYSTEM };
struct ttm_buffer_object *ghost;
+ struct ttm_tt *ttm;
int ret;

- ret = ttm_buffer_object_transfer(bo, &ghost);
+ /* If already idle, no need for ghost object dance. */
+ ret = ttm_bo_wait(bo, false, true);
+ if (ret != -EBUSY) {
+ if (!bo->ttm) {
+ /* See comment below about clearing. */
+ ret = ttm_tt_create(bo, true);
+ if (ret)
+ return ret;
+ } else {
+ ttm_tt_unpopulate(bo->bdev, bo->ttm);
+ if (bo->type == ttm_bo_type_device)
+ ttm_tt_mark_for_clear(bo->ttm);
+ }
+ ttm_resource_free(bo, &bo->mem);
+ ttm_resource_alloc(bo, &sys_mem, &bo->mem);
+
+ return 0;
+ }
+
+ /*
+ * We need an unpopulated ttm_tt after giving our current one,
+ * if any, to the ghost object. And we can't afford to fail
+ * creating one *after* the operation. If the bo subsequently gets
+ * resurrected, make sure it's cleared (if ttm_bo_type_device)
+ * to avoid leaking sensitive information to user-space.
+ */
+
+ ttm = bo->ttm;
+ bo->ttm = NULL;
+ ret = ttm_tt_create(bo, true);
+ swap(bo->ttm, ttm);
if (ret)
return ret;

+ ret = ttm_buffer_object_transfer(bo, &ghost);
+ if (ret) {
+ ttm_tt_destroy(bo->bdev, ttm);
+ return ret;
+ }
+
ret = dma_resv_copy_fences(&ghost->base._resv, bo->base.resv);
/* Last resort, wait for the BO to be idle when we are OOM */
if (ret)
ttm_bo_wait(bo, false, false);

- ttm_resource_alloc(bo, &sys_mem, &bo->mem);
- bo->ttm = NULL;
-
dma_resv_unlock(&ghost->base._resv);
ttm_bo_put(ghost);
+ bo->ttm = ttm;
+ ttm_resource_alloc(bo, &sys_mem, &bo->mem);

return 0;
}
diff --git a/include/drm/ttm/ttm_tt.h b/include/drm/ttm/ttm_tt.h
index 3102059db726..818680c6a8ed 100644
--- a/include/drm/ttm/ttm_tt.h
+++ b/include/drm/ttm/ttm_tt.h
@@ -170,6 +170,19 @@ int ttm_tt_populate(struct ttm_device *bdev, struct ttm_tt *ttm, struct ttm_oper
*/
void ttm_tt_unpopulate(struct ttm_device *bdev, struct ttm_tt *ttm);

+/**
+ * ttm_tt_mark_for_clear - Mark pages for clearing on populate.
+ *
+ * @ttm: Pointer to the ttm_tt structure
+ *
+ * Marks pages for clearing so that the next time the page vector is
+ * populated, the pages will be cleared.
+ */
+static inline void ttm_tt_mark_for_clear(struct ttm_tt *ttm)
+{
+ ttm->page_flags |= TTM_PAGE_FLAG_ZERO_ALLOC;
+}
+
void ttm_tt_mgr_init(unsigned long num_pages, unsigned long num_dma32_pages);

struct ttm_kmap_iter *ttm_kmap_iter_tt_init(struct ttm_kmap_iter_tt *iter_tt,