On Wed, 16 Jun 2021, Claire Chang wrote:
> 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@xxxxxxxxxxxx>
> ---
> .../reserved-memory/reserved-memory.txt | 36 +++++++++++++++++--
> 1 file changed, 33 insertions(+), 3 deletions(-)
>
> diff --git a/Documentation/devicetree/bindings/reserved-memory/reserved-memory.txt b/Documentation/devicetree/bindings/reserved-memory/reserved-memory.txt
> index e8d3096d922c..46804f24df05 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
> @@ -85,10 +102,11 @@ memory-region-names (optional) - a list of names, one for each corresponding
>
> Example
> -------
> -This example defines 3 contiguous regions are defined for Linux kernel:
> +This example defines 4 contiguous regions for Linux kernel:
> one default of all device drivers (named linux,cma@72000000 and 64MiB in size),
> -one dedicated to the framebuffer device (named framebuffer@78000000, 8MiB), and
> -one for multimedia processing (named multimedia-memory@77000000, 64MiB).
> +one dedicated to the framebuffer device (named framebuffer@78000000, 8MiB),
> +one for multimedia processing (named multimedia-memory@77000000, 64MiB), and
> +one for restricted dma pool (named restricted_dma_reserved@0x50000000, 64MiB).
>
> / {
> #address-cells = <1>;
> @@ -120,6 +138,11 @@ one for multimedia processing (named multimedia-memory@77000000, 64MiB).
> compatible = "acme,multimedia-memory";
> reg = <0x77000000 0x4000000>;
> };
> +
> + restricted_dma_reserved: restricted_dma_reserved {
> + compatible = "restricted-dma-pool";
> + reg = <0x50000000 0x4000000>;
> + };
> };
>
> /* ... */
> @@ -138,4 +161,11 @@ one for multimedia processing (named multimedia-memory@77000000, 64MiB).
> memory-region = <&multimedia_reserved>;
> /* ... */
> };
> +
> + pcie_device: pcie_device@0,0 {
> + reg = <0x83010000 0x0 0x00000000 0x0 0x00100000
> + 0x83010000 0x0 0x00100000 0x0 0x00100000>;
> + memory-region = <&restricted_dma_mem_reserved>;
Shouldn't it be &restricted_dma_reserved ?
