linux-kernel - [PATCH] staging: android: ion: Restrict cache maintenance to dma mapped memory

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Date:   Fri, 9 Feb 2018 22:21:05 -0800 (PST)
From:   Liam Mark <lmark@...eaurora.org>
To:     Laura Abbott <labbott@...hat.com>,
        Sumit Semwal <sumit.semwal@...aro.org>
cc:     Martijn Coenen <maco@...roid.com>, Todd Kjos <tkjos@...roid.com>,
        Arve Hjønnevåg <arve@...roid.com>,
        linux-kernel@...r.kernel.org, devel@...verdev.osuosl.org,
        linaro-mm-sig@...ts.linaro.org
Subject: [PATCH] staging: android: ion: Restrict cache maintenance to dma
 mapped memory

The ION begin_cpu_access and end_cpu_access functions use the
dma_sync_sg_for_cpu and dma_sync_sg_for_device APIs to perform cache
maintenance.

Currently it is possible to apply cache maintenance, via the
begin_cpu_access and end_cpu_access APIs, to ION buffers which are not
dma mapped.

The dma sync sg APIs should not be called on sg lists which have not been
dma mapped as this can result in cache maintenance being applied to the
wrong address. If an sg list has not been dma mapped then its dma_address
field has not been populated, some dma ops such as the swiotlb_dma_ops ops
use the dma_address field to calculate the address onto which to apply
cache maintenance.

Fix the ION begin_cpu_access and end_cpu_access functions to only apply
cache maintenance to buffers which have been dma mapped.

Fixes: 2a55e7b5e544 ("staging: android: ion: Call dma_map_sg for syncing and mapping")
Signed-off-by: Liam Mark <lmark@...eaurora.org>
---
 drivers/staging/android/ion/ion.c | 16 ++++++++++++----
 1 file changed, 12 insertions(+), 4 deletions(-)

diff --git a/drivers/staging/android/ion/ion.c b/drivers/staging/android/ion/ion.c
index f480885e346b..e5df5272823d 100644
--- a/drivers/staging/android/ion/ion.c
+++ b/drivers/staging/android/ion/ion.c
@@ -214,6 +214,7 @@ struct ion_dma_buf_attachment {
 	struct device *dev;
 	struct sg_table *table;
 	struct list_head list;
+	bool dma_mapped;
 };
 
 static int ion_dma_buf_attach(struct dma_buf *dmabuf, struct device *dev,
@@ -235,6 +236,7 @@ static int ion_dma_buf_attach(struct dma_buf *dmabuf, struct device *dev,
 
 	a->table = table;
 	a->dev = dev;
+	a->dma_mapped = false;
 	INIT_LIST_HEAD(&a->list);
 
 	attachment->priv = a;
@@ -272,6 +274,7 @@ static struct sg_table *ion_map_dma_buf(struct dma_buf_attachment *attachment,
 			direction))
 		return ERR_PTR(-ENOMEM);
 
+	a->dma_mapped = true;
 	return table;
 }
 
@@ -279,7 +282,10 @@ static void ion_unmap_dma_buf(struct dma_buf_attachment *attachment,
 			      struct sg_table *table,
 			      enum dma_data_direction direction)
 {
+	struct ion_dma_buf_attachment *a = attachment->priv;
+
 	dma_unmap_sg(attachment->dev, table->sgl, table->nents, direction);
+	a->dma_mapped = false;
 }
 
 static int ion_mmap(struct dma_buf *dmabuf, struct vm_area_struct *vma)
@@ -345,8 +351,9 @@ static int ion_dma_buf_begin_cpu_access(struct dma_buf *dmabuf,
 
 	mutex_lock(&buffer->lock);
 	list_for_each_entry(a, &buffer->attachments, list) {
-		dma_sync_sg_for_cpu(a->dev, a->table->sgl, a->table->nents,
-				    direction);
+		if (a->dma_mapped)
+			dma_sync_sg_for_cpu(a->dev, a->table->sgl,
+					    a->table->nents, direction);
 	}
 	mutex_unlock(&buffer->lock);
 
@@ -367,8 +374,9 @@ static int ion_dma_buf_end_cpu_access(struct dma_buf *dmabuf,
 
 	mutex_lock(&buffer->lock);
 	list_for_each_entry(a, &buffer->attachments, list) {
-		dma_sync_sg_for_device(a->dev, a->table->sgl, a->table->nents,
-				       direction);
+		if (a->dma_mapped)
+			dma_sync_sg_for_device(a->dev, a->table->sgl,
+					       a->table->nents, direction);
 	}
 	mutex_unlock(&buffer->lock);
 
-- 
1.8.5.2


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