[PATCH v7 14/15] dt-bindings: of: Add restricted DMA pool

Claire Chang
2021-05-18T06:44:40Z

Introduce the new compatible string, restricted-dma-pool, for restricted
DMA. One can specify the address and length of the restricted DMA memory
region by restricted-dma-pool in the reserved-memory node.

Signed-off-by: Claire Chang <tientzu@chromium.org>
---
.../reserved-memory/reserved-memory.txt | 27 +++++++++++++++++++
1 file changed, 27 insertions(+)

diff --git a/Documentation/devicetree/bindings/reserved-memory/reserved-memory.txt b/Documentation/devicetree/bindings/reserved-memory/reserved-memory.txt
index e8d3096d922c..284aea659015 100644
--- a/Documentation/devicetree/bindings/reserved-memory/reserved-memory.txt
+++ b/Documentation/devicetree/bindings/reserved-memory/reserved-memory.txt
@@ -51,6 +51,23 @@ compatible (optional) - standard definition
used as a shared pool of DMA buffers for a set of devices. It can
be used by an operating system to instantiate the necessary pool
management subsystem if necessary.
+ - restricted-dma-pool: This indicates a region of memory meant to be
+ used as a pool of restricted DMA buffers for a set of devices. The
+ memory region would be the only region accessible to those devices.
+ When using this, the no-map and reusable properties must not be set,
+ so the operating system can create a virtual mapping that will be used
+ for synchronization. The main purpose for restricted DMA is to
+ mitigate the lack of DMA access control on systems without an IOMMU,
+ which could result in the DMA accessing the system memory at
+ unexpected times and/or unexpected addresses, possibly leading to data
+ leakage or corruption. The feature on its own provides a basic level
+ of protection against the DMA overwriting buffer contents at
+ unexpected times. However, to protect against general data leakage and
+ system memory corruption, the system needs to provide way to lock down
+ the memory access, e.g., MPU. Note that since coherent allocation
+ needs remapping, one must set up another device coherent pool by
+ shared-dma-pool and use dma_alloc_from_dev_coherent instead for atomic
+ coherent allocation.
- vendor specific string in the form <vendor>,[<device>-]<usage>
no-map (optional) - empty property
- Indicates the operating system must not create a virtual mapping
@@ -120,6 +137,11 @@ one for multimedia processing (named multimedia-memory@77000000, 64MiB).
compatible = "acme,multimedia-memory";
reg = <0x77000000 0x4000000>;
};
+
+ restricted_dma_mem_reserved: restricted_dma_mem_reserved {
+ compatible = "restricted-dma-pool";
+ reg = <0x50000000 0x400000>;
+ };
};

/* ... */
@@ -138,4 +160,9 @@ one for multimedia processing (named multimedia-memory@77000000, 64MiB).
memory-region = <&multimedia_reserved>;
/* ... */
};
+
+ pcie_device: pcie_device@0,0 {
+ memory-region = <&restricted_dma_mem_reserved>;
+ /* ... */
+ };
};
--
2.31.1.751.gd2f1c929bd-goog