drm/i915: Check scratch page for stray writesscratch_page

Check scratch page contents before freeing it and
report errors if any stray writes are detected.

Signed-off-by: Mika Kuoppala <mika.kuoppala@intel.com>

1 files changed, 19 insertions, 0 deletions

diff --git a/drivers/gpu/drm/i915/i915_gem_gtt.c b/drivers/gpu/drm/i915/i915_gem_gtt.c
index a65c2c4a9785..45254faa5854 100644
--- a/drivers/gpu/drm/i915/i915_gem_gtt.c
+++ b/drivers/gpu/drm/i915/i915_gem_gtt.c
@@ -2345,6 +2345,23 @@ static int alloc_scratch_page(struct i915_address_space *vm)
 	return 0;
 }
 
+static void check_scratch_page(struct i915_address_space *vm)
+{
+	u32 i, *vaddr;
+
+	vaddr = kmap_atomic(vm->scratch_page->page);
+
+	for (i = 0; i < PAGE_SIZE / sizeof(u32); i++) {
+		if (vaddr[i] == 0xffffffff)
+			continue;
+
+		DRM_ERROR("%p scratch[%u] = 0x%08x\n", vm, i, vaddr[i]);
+		break;
+	}
+
+	kunmap_atomic(vaddr);
+}
+
 static void free_scratch_page(struct i915_address_space *vm)
 {
 	struct i915_page_scratch *sp = vm->scratch_page;
@@ -2352,6 +2369,8 @@ static void free_scratch_page(struct i915_address_space *vm)
 	set_pages_wb(sp->page, 1);
 	i915_dma_unmap_px(vm->dev, sp);
 
+	check_scratch_page(vm);
+
 	__free_page(sp->page);
 	kfree(sp);