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Mark Rutland 1db5cdeccd arm64: cpufeature: add cpus_have_final_cap() When cpus_have_const_cap() was originally introduced it was intended to be safe in hyp context, where it is not safe to access the cpu_hwcaps array as cpus_have_cap() did. For more details see commit: `a4023f6827` ("arm64: Add hypervisor safe helper for checking constant capabilities") We then made use of cpus_have_const_cap() throughout the kernel. Subsequently, we had to defer updating the static_key associated with each capability in order to avoid lockdep complaints. To avoid breaking kernel-wide usage of cpus_have_const_cap(), this was updated to fall back to the cpu_hwcaps array if called before the static_keys were updated. As the kvm hyp code was only called later than this, the fallback is redundant but not functionally harmful. For more details, see commit: `63a1e1c95e` ("arm64/cpufeature: don't use mutex in bringup path") Today we have more users of cpus_have_const_cap() which are only called once the relevant static keys are initialized, and it would be beneficial to avoid the redundant code. To that end, this patch adds a new cpus_have_final_cap(), helper which is intend to be used in code which is only run once capabilities have been finalized, and will never check the cpus_hwcap array. This helps the compiler to generate better code as it no longer needs to generate code to address and test the cpus_hwcap array. To help catch misuse, cpus_have_final_cap() will BUG() if called before capabilities are finalized. In hyp context, BUG() will result in a hyp panic, but the specific BUG() instance will not be identified in the usual way. Comments are added to the various cpus_have_*_cap() helpers to describe the constraints on when they can be used. For clarity cpus_have_cap() is moved above the other helpers. Similarly the helpers are updated to use system_capabilities_finalized() consistently, and this is made __always_inline as required by its new callers. Signed-off-by: Mark Rutland <mark.rutland@arm.com> Reviewed-by: Marc Zyngier <maz@kernel.org> Reviewed-by: Suzuki K Poulose <suzuki.poulose@arm.com> Cc: Will Deacon <will@kernel.org> Signed-off-by: Catalin Marinas <catalin.marinas@arm.com>		History 2020-03-13 17:34:25 +00:00
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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.