dma-buf: heaps: Skip sync if not mapped

This patch is basically a port of Ørjan Eide's similar patch for ION
https://lore.kernel.org/lkml/[e-mail]/

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 <[e-mail]>

Cc: Sumit Semwal <[e-mail]>
Cc: Liam Mark <[e-mail]>
Cc: Laura Abbott <[e-mail]>
Cc: Brian Starkey <[e-mail]>
Cc: Hridya Valsaraju <[e-mail]>
Cc: Suren Baghdasaryan <[e-mail]>
Cc: Sandeep Patil <[e-mail]>
Cc: Daniel Mentz <[e-mail]>
Cc: Chris Goldsworthy <[e-mail]>
Cc: Ørjan Eide <[e-mail]>
Cc: Robin Murphy <[e-mail]>
Cc: Ezequiel Garcia <[e-mail]>
Cc: Simon Ser <[e-mail]>
Cc: James Jones <[e-mail]>
Cc: [e-mail]
Cc: [e-mail]
Reviewed-by: Brian Starkey <[e-mail]>
Signed-off-by: John Stultz <[e-mail]>
Signed-off-by: Sumit Semwal <[e-mail]>
Link: https://patchwork.freedesktop.org/patch/msgid/[e-mail]

drivers/dma-buf/heaps/cma_heap.c

···
 	struct device *dev;
 	struct sg_table table;
 	struct list_head list;
+	bool mapped;
 };
 
 static int cma_heap_attach(struct dma_buf *dmabuf,
···
 
 	a->dev = attachment->dev;
 	INIT_LIST_HEAD(&a->list);
+	a->mapped = false;
 
 	attachment->priv = a;
 
···
 	ret = dma_map_sgtable(attachment->dev, table, direction, 0);
 	if (ret)
 		return ERR_PTR(-ENOMEM);
+	a->mapped = true;
 	return table;
 }
 
···
 				   struct sg_table *table,
 				   enum dma_data_direction direction)
 {
+	struct dma_heap_attachment *a = attachment->priv;
+
+	a->mapped = false;
 	dma_unmap_sgtable(attachment->dev, table, direction, 0);
 }
 
···
 
 	mutex_lock(&buffer->lock);
 	list_for_each_entry(a, &buffer->attachments, list) {
+		if (!a->mapped)
+			continue;
 		dma_sync_sgtable_for_cpu(a->dev, &a->table, direction);
 	}
 	mutex_unlock(&buffer->lock);
···
 
 	mutex_lock(&buffer->lock);
 	list_for_each_entry(a, &buffer->attachments, list) {
+		if (!a->mapped)
+			continue;
 		dma_sync_sgtable_for_device(a->dev, &a->table, direction);
 	}
 	mutex_unlock(&buffer->lock);

drivers/dma-buf/heaps/system_heap.c

···
 	struct device *dev;
 	struct sg_table *table;
 	struct list_head list;
+	bool mapped;
 };
 
 static struct sg_table *dup_sg_table(struct sg_table *table)
···
 	a->table = table;
 	a->dev = attachment->dev;
 	INIT_LIST_HEAD(&a->list);
+	a->mapped = false;
 
 	attachment->priv = a;
 
···
 	if (ret)
 		return ERR_PTR(ret);
 
+	a->mapped = true;
 	return table;
 }
 
···
 				      struct sg_table *table,
 				      enum dma_data_direction direction)
 {
+	struct dma_heap_attachment *a = attachment->priv;
+
+	a->mapped = false;
 	dma_unmap_sgtable(attachment->dev, table, direction, 0);
 }
 
···
 		invalidate_kernel_vmap_range(buffer->vaddr, buffer->len);
 
 	list_for_each_entry(a, &buffer->attachments, list) {
+		if (!a->mapped)
+			continue;
 		dma_sync_sgtable_for_cpu(a->dev, a->table, direction);
 	}
 	mutex_unlock(&buffer->lock);
···
 		flush_kernel_vmap_range(buffer->vaddr, buffer->len);
 
 	list_for_each_entry(a, &buffer->attachments, list) {
+		if (!a->mapped)
+			continue;
 		dma_sync_sgtable_for_device(a->dev, a->table, direction);
 	}
 	mutex_unlock(&buffer->lock);