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Some platforms, like many ARM SoCs, require the ability to run code from on-chip memory like SRAM for tasks like reconfiguring the SDRAM controller or entering low-power sleep modes. In order to do this we must be able to allocate memory that the code can be copied to but then change the mapping to be read-only and executable so that no memory is both writable and executable at the same time to avoid opening any unneccesary security holes. By using the existing "pool" partition type that the SRAM driver allows we can create a memory space that will already be exposed by the genalloc framework to allow for allocating memory but we must extend this to meet the executable requirements. By making use of various set_memory_* APIs we can change the attributes of pages to make them writable for code upload but then read-only and executable when we want to actually run code. Because SRAM is a shared resource we need a centralized manager of these set memory calls. Because the SRAM driver itself is responsible for allocating the memory we can introduce a sram_copy_exec API for the driver that works like memcpy but also manages the page attributes and locking to allow multiple users of the same SRAM space to all copy their code over independent of other each before starting execution. It is maintained in a separate file from the core SRAM driver to allow it to be selectively built depending on whether or not a platform has the appropriate set_memory_* APIs. A future patch will integrate it with the core SRAM driver. Signed-off-by: Dave Gerlach <d-gerlach@ti.com> Acked-by: Tony Lindgren <tony@atomide.com> Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org> |
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Linux kernel ============ This file was moved to Documentation/admin-guide/README.rst Please notice that there are several guides for kernel developers and users. These guides can be rendered in a number of formats, like HTML and PDF. In order to build the documentation, use ``make htmldocs`` or ``make pdfdocs``. There are various text files in the Documentation/ subdirectory, several of them using the Restructured Text markup notation. See Documentation/00-INDEX for a list of what is contained in each file. Please read the Documentation/process/changes.rst file, as it contains the requirements for building and running the kernel, and information about the problems which may result by upgrading your kernel.