Re: Updated version of RD/WR FS/GS BASE patchkit
From: Andi Kleen
Date: Mon Mar 21 2016 - 18:52:54 EST
> No. My objection is that there needs to be an explicit statement what
> the semantics are. If the agreed-upon semantics are "undefined
> behavior if GS != 0 and GSBASE doesn't match the descriptor", so be
> it, but this needs to be a conscious decision and needs to be weighed
> against the alternatives.
Documentation/x86/fsgs.txt already has this statement:
>>>
Another requirement is that the FS or GS selector has to be zero
(is normally true unless changed explicitly). When it is non-zero
the context switch assumes the bases were loaded through the LDT/GDT,
and will reload that.
<<<
Is that sufficient?
>
> The actual implementation details are just details. They need to
> match the intended semantics, of course.
I believe my implementation matches the paragraph above.
-Andi
--
ak@xxxxxxxxxxxxxxx -- Speaking for myself only.