drm/i915/gem: Flush all the reloc_gpu batch

__i915_gem_object_flush_map() takes a byte range, so feed it the written
bytes and do not mistake the u32 index as bytes!

Fixes: a679f58d ("drm/i915: Flush pages on acquisition")
Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Cc: Matthew Auld <matthew.william.auld@gmail.com>
Cc: <stable@vger.kernel.org> # v5.2+
Reviewed-by: Matthew Auld <matthew.william.auld@gmail.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20200406114821.10949-1-chris@chris-wilson.co.uk

drivers/gpu/drm/i915/gem/i915_gem_execbuffer.c

@@ -977,11 +977,13 @@ static inline struct i915_ggtt *cache_to_ggtt(struct reloc_cache *cache)
 
 static void reloc_gpu_flush(struct reloc_cache *cache)
 {
-	GEM_BUG_ON(cache->rq_size >= cache->rq->batch->obj->base.size / sizeof(u32));
+	struct drm_i915_gem_object *obj = cache->rq->batch->obj;
+
+	GEM_BUG_ON(cache->rq_size >= obj->base.size / sizeof(u32));
 	cache->rq_cmd[cache->rq_size] = MI_BATCH_BUFFER_END;
 
-	__i915_gem_object_flush_map(cache->rq->batch->obj, 0, cache->rq_size);
-	i915_gem_object_unpin_map(cache->rq->batch->obj);
+	__i915_gem_object_flush_map(obj, 0, sizeof(u32) * (cache->rq_size + 1));
+	i915_gem_object_unpin_map(obj);
 
 	intel_gt_chipset_flush(cache->rq->engine->gt);