The February 2022 microcode is formally de-featuring TSX on the TAA-impacted
client CPUs. The backup TAA mitigation (VERW regaining its flushing side
effect) is being dropped, meaning that `smt=0 spec-ctrl=md-clear` no longer
protects against TAA on these parts.
The new functionality enumerates itself via the RTM_ALWAYS_ABORT CPUID
bit (the same as June 2021), but has its control in MSR_MCU_OPT_CTRL as
opposed to MSR_TSX_FORCE_ABORT.
TSX now defaults to being disabled on ucode load. Furthermore, if SGX is
enabled in the BIOS, TSX is locked and cannot be re-enabled. In this case,
override opt_tsx to 0, so the RTM/HLE CPUID bits get hidden by default.
While updating the command line documentation, take the opportunity to add a
paragraph explaining what TSX being disabled actually means, and how migration
compatibility works.
Signed-off-by: Andrew Cooper <andrew.cooper3@citrix.com>
Reviewed-by: Jan Beulich <jbeulich@suse.com>
Andrew Cooper
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