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

From: Christoph Hellwig <hch@lst.de>
To: Amit Pundir <amit.pundir@linaro.org>
Cc: lkml <linux-kernel@vger.kernel.org>,
	jeremy.linton@arm.com, Sumit Semwal <sumit.semwal@linaro.org>,
	iommu@lists.linux-foundation.org,
	John Stultz <john.stultz@linaro.org>,
	linux-rpi-kernel@lists.infradead.org,
	David Rientjes <rientjes@google.com>,
	Robin Murphy <robin.murphy@arm.com>,
	Christoph Hellwig <hch@lst.de>
Subject: Re: [PATCH] dma-pool: Do not allocate pool memory from CMA
Date: Fri, 24 Jul 2020 15:41:14 +0200	[thread overview]
Message-ID: <20200724134114.GA3152@lst.de> (raw)
In-Reply-To: <CAMi1Hd3O2HHBsnt=sac7FdcW0-3=4S3g_F9f__2h5gTsudfirA@mail.gmail.com>

Yes, the iommu is an interesting case, and the current code is
wrong for that.  Can you try the patch below?  It contains a modified
version of Nicolas' patch to try CMA again for the expansion and a new
(for now hackish) way to not apply the addressability check for dma-iommu
allocations.

diff --git a/kernel/dma/pool.c b/kernel/dma/pool.c
index 6bc74a2d51273e..ec5e525d2b9309 100644
--- a/kernel/dma/pool.c
+++ b/kernel/dma/pool.c
@@ -3,7 +3,9 @@
  * Copyright (C) 2012 ARM Ltd.
  * Copyright (C) 2020 Google LLC
  */
+#include <linux/cma.h>
 #include <linux/debugfs.h>
+#include <linux/dma-contiguous.h>
 #include <linux/dma-direct.h>
 #include <linux/dma-noncoherent.h>
 #include <linux/init.h>
@@ -55,6 +57,31 @@ static void dma_atomic_pool_size_add(gfp_t gfp, size_t size)
 		pool_size_kernel += size;
 }
 
+static bool cma_in_zone(gfp_t gfp)
+{
+	phys_addr_t end;
+	unsigned long size;
+	struct cma *cma;
+
+	cma = dev_get_cma_area(NULL);
+	if (!cma)
+		return false;
+
+	size = cma_get_size(cma);
+	if (!size)
+		return false;
+	end = cma_get_base(cma) - memblock_start_of_DRAM() + size - 1;
+
+	/* CMA can't cross zone boundaries, see cma_activate_area() */
+	if (IS_ENABLED(CONFIG_ZONE_DMA) && (gfp & GFP_DMA) &&
+	    end <= DMA_BIT_MASK(zone_dma_bits))
+		return true;
+	if (IS_ENABLED(CONFIG_ZONE_DMA32) && (gfp & GFP_DMA32) &&
+	    end <= DMA_BIT_MASK(32))
+		return true;
+	return true;
+}
+
 static int atomic_pool_expand(struct gen_pool *pool, size_t pool_size,
 			      gfp_t gfp)
 {
@@ -68,7 +95,11 @@ static int atomic_pool_expand(struct gen_pool *pool, size_t pool_size,
 
 	do {
 		pool_size = 1 << (PAGE_SHIFT + order);
-		page = alloc_pages(gfp, order);
+		if (cma_in_zone(gfp))
+ 			page = dma_alloc_from_contiguous(NULL, 1 << order,
+ 							 order, false);
+		if (!page)
+			page = alloc_pages(gfp, order);
 	} while (!page && order-- > 0);
 	if (!page)
 		goto out;
@@ -251,7 +282,11 @@ void *dma_alloc_from_pool(struct device *dev, size_t size,
 			continue;
 
 		phys = gen_pool_virt_to_phys(pool, val);
-		if (dma_coherent_ok(dev, phys, size))
+		/*
+		 * Only apply the addressability check for dma-direct.
+		 * This is a nasty hack and won't work e.g. for arm.
+		 */
+		if (get_dma_ops(dev) || dma_coherent_ok(dev, phys, size))
 			break;
 
 		gen_pool_free(pool, val, size);
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