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A mirror of the official Linux kernel repository just in case
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As with SCTLR_ELx and other control registers, some PSTATE bits are UNKNOWN out-of-reset, and we may not be able to rely on hardware or firmware to initialize them to our liking prior to entry to the kernel, e.g. in the primary/secondary boot paths and return from idle/suspend. It would be more robust (and easier to reason about) if we consistently initialized PSTATE to a default value, as we do with control registers. This will ensure that the kernel is not adversely affected by bits it is not aware of, e.g. when support for a feature such as PAN/UAO is disabled. This patch ensures that PSTATE is consistently initialized at boot time via an ERET. This is not intended to relax the existing requirements (e.g. DAIF bits must still be set prior to entering the kernel). For features detected dynamically (which may require system-wide support), it is still necessary to subsequently modify PSTATE. As ERET is not always a Context Synchronization Event, an ISB is placed before each exception return to ensure updates to control registers have taken effect. This handles the kernel being entered with SCTLR_ELx.EOS clear (or any future control bits being in an UNKNOWN state). Signed-off-by: Mark Rutland <mark.rutland@arm.com> Cc: Christoph Hellwig <hch@lst.de> Cc: James Morse <james.morse@arm.com> Cc: Will Deacon <will@kernel.org> Link: https://lore.kernel.org/r/20201113124937.20574-6-mark.rutland@arm.com Signed-off-by: Catalin Marinas <catalin.marinas@arm.com> |
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| README | ||
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.