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Upon entering or exiting a guest we may modify multiple PMU counters to enable of disable EL0 filtering. We presently do this via the indirect PMXEVTYPER_EL0 system register (where the counter we modify is selected by PMSELR). With this approach it is necessary to order the writes via isb instructions such that we select the correct counter before modifying it. Let's avoid potentially expensive instruction barriers by using the direct PMEVTYPER<n>_EL0 registers instead. As the change to counter type relates only to EL0 filtering we can rely on the implicit instruction barrier which occurs when we transition from EL2 to EL1 on entering the guest. On returning to userspace we can, at the latest, rely on the implicit barrier between EL2 and EL0. We can also depend on the explicit isb in armv8pmu_select_counter to order our write against any other kernel changes by the PMU driver to the type register as a result of preemption. Signed-off-by: Andrew Murray <andrew.murray@arm.com> Reviewed-by: Suzuki K Poulose <suzuki.poulose@arm.com> Signed-off-by: Marc Zyngier <marc.zyngier@arm.com>
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.