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arm64: mm: faster linear map creation

Eric Chanudet requested to merge echanude/centos-stream-9:faster-lm-init into main

JIRA: https://issues.redhat.com/browse/RHEL-32699

The linear map creation silently takes a significant amount of time on arm64
platforms that boots with rodata=full (see RODATA_FULL_DEFAULT_ENABLED, which
is set by default on cs9). This was attended upstream through a refactoring to
avoid superflous tlb invalidations and batch memory barriers.

For the automotive use-case, this is particularly interesting, as the setting
up the linear map takes a prohibitive amount of time on targeted platforms (e,g
on sa8775p-ride, map_mem() takes ~358ms, compared to only ~35ms with this
series).

This backport draft arbitrarily chooses to limit the amount of changes
backported, therefor introducing conflicts, as this series was introduced
after the following changeset:

Signed-off-by: Eric Chanudet echanude@redhat.com

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