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Arm Changing Linux Default To Costly "KPTI" Mitigation For Some Newer CPUs
For some newer Arm core designs, Arm is changing the Linux kernel to defaulting to enabling Kernel Page Table Isolation 'KPTI' if not running on a new firmware version in order to properly mitigate a recently disclosed CPU security issue
Unfortunately, it's turned out to be needed for some newer Arm core designs if not having a new firmware in place with an alternative mitigation strategy. To facilitate this, Arm has updated the SMC Calling Convention spec so that privileged normal world software can identify when the issue has been mitigated in firmware (SMCCC_ARCH_WORKAROUND_4)." So the KPTI performance nightmare is unfortunately coming back to newer Arm CPUs if not having updated firmware available on affected models.
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