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Most I/O in the kernel is done using the kernel offset mapping. However, there is one API that uses aliased kernel address ranges: > The final category of APIs is for I/O to deliberately aliased address > ranges inside the kernel. Such aliases are set up by use of the > vmap/vmalloc API. Since kernel I/O goes via physical pages, the I/O > subsystem assumes that the user mapping and kernel offset mapping are > the only aliases. This isn't true for vmap aliases, so anything in > the kernel trying to do I/O to vmap areas must manually manage > coherency. It must do this by flushing the vmap range before doing > I/O and invalidating it after the I/O returns. For this reason, we should use the hardware lpa instruction to load the physical address of kernel virtual addresses in the driver code. I believe we only use the vmap/vmalloc API with old PA 1.x processors which don't have a sba, so we don't hit this problem. Tested on c3750, c8000 and rp3440. Signed-off-by: John David Anglin <dave.anglin@bell.net> Signed-off-by: Helge Deller <deller@gmx.de>
Linux kernel
============
There are several guides for kernel developers and users. These guides can
be rendered in a number of formats, like HTML and PDF. Please read
Documentation/admin-guide/README.rst first.
In order to build the documentation, use ``make htmldocs`` or
``make pdfdocs``. The formatted documentation can also be read online at:
https://www.kernel.org/doc/html/latest/
There are various text files in the Documentation/ subdirectory,
several of them using the Restructured Text markup notation.
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.