[RFC][PATCH 6/6] dma-buf: heaps: Skip sync if not mapped

[John Stultz]

This patch is basically a port of Ørjan Eide's similar patch for ION
 https://lore.kernel.org/lkml/20200414134629.54567-1-orjan.eide@xxxxxxx/

Only sync the sg-list of dma-buf heap attachment when the attachment
is actually mapped on the device.

dma-bufs may be synced at any time. It can be reached from user space
via DMA_BUF_IOCTL_SYNC, so there are no guarantees from callers on when
syncs may be attempted, and dma_buf_end_cpu_access() and
dma_buf_begin_cpu_access() may not be paired.

Since the sg_list's dma_address isn't set up until the buffer is used
on the device, and dma_map_sg() is called on it, the dma_address will be
NULL if sync is attempted on the dma-buf before it's mapped on a device.

Before v5.0 (commit 55897af63091 ("dma-direct: merge swiotlb_dma_ops
into the dma_direct code")) this was a problem as the dma-api (at least
the swiotlb_dma_ops on arm64) would use the potentially invalid
dma_address. How that failed depended on how the device handled physical
address 0. If 0 was a valid address to physical ram, that page would get
flushed a lot, while the actual pages in the buffer would not get synced
correctly. While if 0 is an invalid physical address it may cause a
fault and trigger a crash.

In v5.0 this was incidentally fixed by commit 55897af63091 ("dma-direct:
merge swiotlb_dma_ops into the dma_direct code"), as this moved the
dma-api to use the page pointer in the sg_list, and (for Ion buffers at
least) this will always be valid if the sg_list exists at all.

But, this issue is re-introduced in v5.3 with
commit 449fa54d6815 ("dma-direct: correct the physical addr in
dma_direct_sync_sg_for_cpu/device") moves the dma-api back to the old
behaviour and picks the dma_address that may be invalid.

dma-buf core doesn't ensure that the buffer is mapped on the device, and
thus have a valid sg_list, before calling the exporter's
begin_cpu_access.

Logic and commit message originally by: Ørjan Eide <orjan.eide@xxxxxxx>

Cc: Sumit Semwal <sumit.semwal@xxxxxxxxxx>
Cc: Liam Mark <lmark@xxxxxxxxxxxxxx>
Cc: Laura Abbott <labbott@xxxxxxxxxx>
Cc: Brian Starkey <Brian.Starkey@xxxxxxx>
Cc: Hridya Valsaraju <hridya@xxxxxxxxxx>
Cc: Suren Baghdasaryan <surenb@xxxxxxxxxx>
Cc: Sandeep Patil <sspatil@xxxxxxxxxx>
Cc: Ørjan Eide <orjan.eide@xxxxxxx>
Cc: Robin Murphy <robin.murphy@xxxxxxx>
Cc: Ezequiel Garcia <ezequiel@xxxxxxxxxxxxx>
Cc: Simon Ser <contact@xxxxxxxxxxx>
Cc: James Jones <jajones@xxxxxxxxxx>
Cc: linux-media@xxxxxxxxxxxxxxx
Cc: dri-devel@xxxxxxxxxxxxxxxxxxxxx
Signed-off-by: John Stultz <john.stultz@xxxxxxxxxx>
---
 drivers/dma-buf/heaps/cma_heap.c    | 10 ++++++++++
 drivers/dma-buf/heaps/system_heap.c | 10 ++++++++++
 2 files changed, 20 insertions(+)

diff --git a/drivers/dma-buf/heaps/cma_heap.c b/drivers/dma-buf/heaps/cma_heap.c
index 3adfdbed0829..b6ab0392ad9a 100644
--- a/drivers/dma-buf/heaps/cma_heap.c
+++ b/drivers/dma-buf/heaps/cma_heap.c
@@ -44,6 +44,7 @@ struct dma_heap_attachment {
 	struct device *dev;
 	struct sg_table table;
 	struct list_head list;
+	bool mapped;
 };
 
 static int cma_heap_attach(struct dma_buf *dmabuf,
@@ -68,6 +69,7 @@ static int cma_heap_attach(struct dma_buf *dmabuf,
 
 	a->dev = attachment->dev;
 	INIT_LIST_HEAD(&a->list);
+	a->mapped = false;
 
 	attachment->priv = a;
 
@@ -101,6 +103,7 @@ static struct sg_table *cma_heap_map_dma_buf(struct dma_buf_attachment *attachme
 	if (!dma_map_sg(attachment->dev, table->sgl, table->nents,
 			direction))
 		table = ERR_PTR(-ENOMEM);
+	a->mapped = true;
 	return table;
 }
 
@@ -108,6 +111,9 @@ static void cma_heap_unmap_dma_buf(struct dma_buf_attachment *attachment,
 				   struct sg_table *table,
 				   enum dma_data_direction direction)
 {
+	struct dma_heap_attachment *a = attachment->priv;
+
+	a->mapped = false;
 	dma_unmap_sg(attachment->dev, table->sgl, table->nents, direction);
 }
 
@@ -123,6 +129,8 @@ static int cma_heap_dma_buf_begin_cpu_access(struct dma_buf *dmabuf,
 
 	mutex_lock(&buffer->lock);
 	list_for_each_entry(a, &buffer->attachments, list) {
+		if (!a->mapped)
+			continue;
 		dma_sync_sg_for_cpu(a->dev, a->table.sgl, a->table.nents,
 				    direction);
 	}
@@ -142,6 +150,8 @@ static int cma_heap_dma_buf_end_cpu_access(struct dma_buf *dmabuf,
 
 	mutex_lock(&buffer->lock);
 	list_for_each_entry(a, &buffer->attachments, list) {
+		if (!a->mapped)
+			continue;
 		dma_sync_sg_for_device(a->dev, a->table.sgl, a->table.nents,
 				       direction);
 	}
diff --git a/drivers/dma-buf/heaps/system_heap.c b/drivers/dma-buf/heaps/system_heap.c
index 9f57b4c8ae69..8a523b6fd51a 100644
--- a/drivers/dma-buf/heaps/system_heap.c
+++ b/drivers/dma-buf/heaps/system_heap.c
@@ -38,6 +38,7 @@ struct dma_heap_attachment {
 	struct device *dev;
 	struct sg_table *table;
 	struct list_head list;
+	bool mapped;
 };
 
 #define HIGH_ORDER_GFP  (((GFP_HIGHUSER | __GFP_ZERO | __GFP_NOWARN \
@@ -94,6 +95,7 @@ static int system_heap_attach(struct dma_buf *dmabuf,
 	a->table = table;
 	a->dev = attachment->dev;
 	INIT_LIST_HEAD(&a->list);
+	a->mapped = false;
 
 	attachment->priv = a;
 
@@ -128,6 +130,7 @@ static struct sg_table *system_heap_map_dma_buf(struct dma_buf_attachment *attac
 	if (!dma_map_sg(attachment->dev, table->sgl, table->nents, direction))
 		return ERR_PTR(-ENOMEM);
 
+	a->mapped = true;
 	return table;
 }
 
@@ -135,6 +138,9 @@ static void system_heap_unmap_dma_buf(struct dma_buf_attachment *attachment,
 				      struct sg_table *table,
 				      enum dma_data_direction direction)
 {
+	struct dma_heap_attachment *a = attachment->priv;
+
+	a->mapped = false;
 	dma_unmap_sg(attachment->dev, table->sgl, table->nents, direction);
 }
 
@@ -151,6 +157,8 @@ static int system_heap_dma_buf_begin_cpu_access(struct dma_buf *dmabuf,
 		invalidate_kernel_vmap_range(buffer->vaddr, buffer->len);
 
 	list_for_each_entry(a, &buffer->attachments, list) {
+		if (!a->mapped)
+			continue;
 		dma_sync_sg_for_cpu(a->dev, a->table->sgl, a->table->nents,
 				    direction);
 	}
@@ -171,6 +179,8 @@ static int system_heap_dma_buf_end_cpu_access(struct dma_buf *dmabuf,
 		flush_kernel_vmap_range(buffer->vaddr, buffer->len);
 
 	list_for_each_entry(a, &buffer->attachments, list) {
+		if (!a->mapped)
+			continue;
 		dma_sync_sg_for_device(a->dev, a->table->sgl, a->table->nents,
 				       direction);
 	}
-- 
2.17.1