0594061ee6
This calls into the Arm Trusted Firmware to enable and disable the workaround for the Speculative Store Bypass Disable (SSBD) issue, also known as Spectre Variant 4. As this may have a large performance overhead, and how exploitable SSBD is is unknown we follow the Linux lead of allowing the administrator to select between always on, always off, or only enabled in the kernel, with the latter being the default. PR: 228955 Sponsored by: DARPA, AFRL Differential Revision: https://reviews.freebsd.org/D15819
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include System include files.
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