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Oliver Upton 2417218f2f KVM: arm64: Get rid of __kvm_get_mdcr_el2() and related warts
KVM caches MDCR_EL2 on a per-CPU basis in order to preserve the
configuration of MDCR_EL2.HPMN while running a guest. This is a bit
gross, since we're relying on some baked configuration rather than the
hardware definition of implemented counters.

Discover the number of implemented counters by reading PMCR_EL0.N
instead. This works because:

 - In VHE the kernel runs at EL2, and N always returns the number of
   counters implemented in hardware

 - In {n,h}VHE, the EL2 setup code programs MDCR_EL2.HPMN with the EL2
   view of PMCR_EL0.N for the host

Lastly, avoid traps under nested virtualization by saving PMCR_EL0.N in
host data.

Tested-by: James Clark <james.clark@linaro.org>
Signed-off-by: Oliver Upton <oliver.upton@linux.dev>
Link: https://lore.kernel.org/r/20241219224116.3941496-3-oliver.upton@linux.dev
Signed-off-by: Marc Zyngier <maz@kernel.org>
History 2024-12-20 08:49:08 +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 reStructuredText 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.