drm/ttm: make sure pool pages are cleared

The old implementation wasn't consistend on this.

But it looks like we depend on this so better bring it back.
Signed-off-by: Christian König <christian.koenig@amd.com>
Reported-and-tested-by: Mike Galbraith <efault@gmx.de>
Fixes: d099fc8f ("drm/ttm: new TT backend allocation pool v3")
Reviewed-by: Daniel Vetter <daniel.vetter@ffwll.ch>
Link: https://patchwork.freedesktop.org/patch/msgid/20210210160549.1462-1-christian.koenig@amd.com

drivers/gpu/drm/ttm/ttm_pool.c

@@ -33,6 +33,7 @@
 
 #include <linux/module.h>
 #include <linux/dma-mapping.h>
+#include <linux/highmem.h>
 
 #ifdef CONFIG_X86
 #include <asm/set_memory.h>
@@ -218,6 +219,15 @@ static void ttm_pool_unmap(struct ttm_pool *pool, dma_addr_t dma_addr,
 /* Give pages into a specific pool_type */
 static void ttm_pool_type_give(struct ttm_pool_type *pt, struct page *p)
 {
+	unsigned int i, num_pages = 1 << pt->order;
+
+	for (i = 0; i < num_pages; ++i) {
+		if (PageHighMem(p))
+			clear_highpage(p + i);
+		else
+			clear_page(page_address(p + i));
+	}
+
 	spin_lock(&pt->lock);
 	list_add(&p->lru, &pt->pages);
 	spin_unlock(&pt->lock);