Re: [PATCH v12 00/18] Enable FSGSBASE instructions

[Andi Kleen]

> Yes, for SGX this is functional feature because enclave entry points,
> thread control structures (aka TCS's), reset FSBASE and GSBASE registers
> to fixed (albeit user defined) values. And syscall's can be done only
> outside of enclave.
> 
> This is a required feature for fancier runtimes (such as Graphene).

Can you please explain a bit more? What do they need GS for?

-Andi