The FSGSBASE instruction allows for reading/write to the FS/GS BASE from any privilege and should help with performance in areas like context switching that has been hurt over the past year and a half due to the likes of Spectre, Meltdown and Foreshadow. User-space programs like Java could also optimize their performance by making use of the FSGSBASE instruction itself to avoid system calls for editing the FS/GS BASE
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