On 02/09/2018 10:21 PM, Liam Mark wrote:
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.

I think this looks okay. I was initially concerned about concurrency and
setting the dma_mapped flag but I think that should be handled by the
caller synchronizing map/unmap/cpu_access calls (we might need to re-evaluate
in the future)

I would like to hold on queuing this for just a little bit until I
finish working on the Ion unit test (doing this in the complete opposite
order of course). I'm assuming this passed your internal tests Liam?

Thanks,
Laura

Fixes: 2a55e7b5e544 ("staging: android: ion: Call dma_map_sg for syncing and 
mapping")
Signed-off-by: Liam Mark <lm...@codeaurora.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;caller 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);

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