linux-kernel - [PATCH] dma-pool: Do not allocate pool memory from CMA

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Date:   Wed,  8 Jul 2020 18:49:39 +0200
From:   Nicolas Saenz Julienne <nsaenzjulienne@...e.de>
To:     Christoph Hellwig <hch@....de>,
        Marek Szyprowski <m.szyprowski@...sung.com>,
        Robin Murphy <robin.murphy@....com>,
        David Rientjes <rientjes@...gle.com>
Cc:     linux-rpi-kernel@...ts.infradead.org, jeremy.linton@....com,
        Nicolas Saenz Julienne <nsaenzjulienne@...e.de>,
        iommu@...ts.linux-foundation.org, linux-kernel@...r.kernel.org
Subject: [PATCH] dma-pool: Do not allocate pool memory from CMA

There is no guarantee to CMA's placement, so allocating a zone specific
atomic pool from CMA might return memory from a completely different
memory zone. So stop using it.

Fixes: c84dc6e68a1d ("dma-pool: add additional coherent pools to map to gfp mask")
Reported-by: Jeremy Linton <jeremy.linton@....com>
Signed-off-by: Nicolas Saenz Julienne <nsaenzjulienne@...e.de>
---

An more costly alternative would be adding an option to
dma_alloc_from_contiguous() so it fails when the allocation doesn't fall
in a specific zone.

 kernel/dma/pool.c | 11 ++---------
 1 file changed, 2 insertions(+), 9 deletions(-)

diff --git a/kernel/dma/pool.c b/kernel/dma/pool.c
index 8cfa01243ed2..4bc1c46ae6ef 100644
--- a/kernel/dma/pool.c
+++ b/kernel/dma/pool.c
@@ -6,7 +6,6 @@
 #include <linux/debugfs.h>
 #include <linux/dma-direct.h>
 #include <linux/dma-noncoherent.h>
-#include <linux/dma-contiguous.h>
 #include <linux/init.h>
 #include <linux/genalloc.h>
 #include <linux/set_memory.h>
@@ -69,12 +68,7 @@ static int atomic_pool_expand(struct gen_pool *pool, size_t pool_size,
 
 	do {
 		pool_size = 1 << (PAGE_SHIFT + order);
-
-		if (dev_get_cma_area(NULL))
-			page = dma_alloc_from_contiguous(NULL, 1 << order,
-							 order, false);
-		else
-			page = alloc_pages(gfp, order);
+		page = alloc_pages(gfp, order);
 	} while (!page && order-- > 0);
 	if (!page)
 		goto out;
@@ -118,8 +112,7 @@ static int atomic_pool_expand(struct gen_pool *pool, size_t pool_size,
 	dma_common_free_remap(addr, pool_size);
 #endif
 free_page: __maybe_unused
-	if (!dma_release_from_contiguous(NULL, page, 1 << order))
-		__free_pages(page, order);
+	__free_pages(page, order);
 out:
 	return ret;
 }
-- 
2.27.0