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Norbert Manthey
3860d5534d
To control the runtime behavior on L1TF vulnerable platforms better, the command line option l1tf-barrier is introduced. This option controls whether on vulnerable x86 platforms the lfence instruction is used to prevent speculative execution from bypassing the evaluation of conditionals that are protected with the evaluate_nospec macro. By now, Xen is capable of identifying L1TF vulnerable hardware. However, this information cannot be used for alternative patching, as a CPU feature is required. To control alternative patching with the command line option, a new x86 feature "X86_FEATURE_SC_L1TF_VULN" is introduced. This feature is used to patch the lfence instruction into the arch_barrier_nospec_true function. The feature is enabled only if L1TF vulnerable hardware is detected and the command line option does not prevent using this feature. The status of hyperthreading is considered when automatically enabling adding the lfence instruction. Since platforms without hyperthreading can still be vulnerable to L1TF in case the L1 cache is not flushed properly, the additional lfence instructions are patched in if either hyperthreading is enabled, or L1 cache flushing is missing. This is part of the speculative hardening effort. Signed-off-by: Norbert Manthey <nmanthey@amazon.de> Reviewed-by: Jan Beulich <jbeulich@suse.com>