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Currently we use the top 4 context ids (0x7fffc-0x7ffff) for the kernel. Kernel VSIDs are built using these top context values and effective the segement ID. In subsequent patches we want to increase the max effective address to 512TB. We will achieve that by increasing the effective segment IDs there by increasing virtual address range. We will be switching to a 68bit virtual address in the following patch. But platforms like Power4 and Power5 only support a 65 bit virtual address. We will handle that by limiting the context bits to 16 instead of 19 on those platforms. That means the max context id will have a different value on different platforms. So that we don't have to deal with the kernel context ids changing between different platforms, move the kernel context ids down to use context ids 1-4. We can't use segment 0 of context-id 0, because that maps to VSID 0, which we want to keep as invalid, so we avoid context-id 0 entirely. Similarly we can't use the last segment of the maximum context, so we avoid it too. Signed-off-by: Aneesh Kumar K.V <aneesh.kumar@linux.vnet.ibm.com> [mpe: Switch from 0-3 to 1-4 so VSID=0 remains invalid] Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
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.