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When a CPU is brought up, it is checked against the caps that are known to be enabled on the system (via verify_local_cpu_capabilities()). Based on the state of the capability on the CPU vs. that of System we could have the following combinations of conflict. x-----------------------------x | Type | System | Late CPU | |-----------------------------| | a | y | n | |-----------------------------| | b | n | y | x-----------------------------x Case (a) is not permitted for caps which are system features, which the system expects all the CPUs to have (e.g VHE). While (a) is ignored for all errata work arounds. However, there could be exceptions to the plain filtering approach. e.g, KPTI is an optional feature for a late CPU as long as the system already enables it. Case (b) is not permitted for errata work arounds that cannot be activated after the kernel has finished booting.And we ignore (b) for features. Here, yet again, KPTI is an exception, where if a late CPU needs KPTI we are too late to enable it (because we change the allocation of ASIDs etc). Add two different flags to indicate how the conflict should be handled. ARM64_CPUCAP_PERMITTED_FOR_LATE_CPU - CPUs may have the capability ARM64_CPUCAP_OPTIONAL_FOR_LATE_CPU - CPUs may not have the cappability. Now that we have the flags to describe the behavior of the errata and the features, as we treat them, define types for ERRATUM and FEATURE. Cc: Will Deacon <will.deacon@arm.com> Cc: Mark Rutland <mark.rutland@arm.com> Reviewed-by: Dave Martin <dave.martin@arm.com> Signed-off-by: Suzuki K Poulose <suzuki.poulose@arm.com> Signed-off-by: Will Deacon <will.deacon@arm.com>
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.