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This commit updates to kernel version 4.9.75 and enables CONFIG_PAGE_TABLE_ISOLATION for x86, x86_64 and aarch64. For all other architectures, CONFIG_PAGE_TABLE_ISOLATION is disabled. CONFIG_PAGE_TABLE_ISOLATION mitigates the Meltdown security flaw almost all Intel CPUs and some ARM CPUs are suspect to [1,2]. (This patch does not solve the Spectre security threat [2], which affects also non-Intel CPUs [3].) I believe this commit will cause some discussion, especially the following points seem worth discussing: a) CONFIG_PAGE_TABLE_ISOLATION has a performance impact on syscalls, which can slow down specific applications significantly. AMD users might benefit from a kernel without KPTI (unless Meltdown turns out to affect them as well) b) Is disabling this feature a reasonable choice for CPU architectures different from x86, x86_64 and aarch64? [1]: https://meltdownattack.com/#faq-systems-meltdown [2]: http://kroah.com/log/blog/2018/01/06/meltdown-status/ [3]: https://meltdownattack.com/#faq-systems-spectre
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