RE: [PATCH 200/208] x86/fpu/xstate: Don't assume the first zero xfeatures zero bit means the end

[Yu, Fenghua]

> From: Ingo Molnar [mailto:mingo.kernel.org@xxxxxxxxx] On Behalf Of Ingo
> Molnar
> Sent: Tuesday, May 05, 2015 10:58 AM
> To: linux-kernel@xxxxxxxxxxxxxxx
> Cc: Andy Lutomirski; Borislav Petkov; Dave Hansen; Yu, Fenghua; H. Peter
> Anvin; Linus Torvalds; Oleg Nesterov; Thomas Gleixner
> Subject: [PATCH 200/208] x86/fpu/xstate: Don't assume the first zero
> xfeatures zero bit means the end
> 
> The current xstate code in setup_xstate_features() assumes that the first
> zero bit means the end of xfeatures - but that is not so, the SDM clearly
> states that an arbitrary set of xfeatures might be enabled - and it is also clear
> from the description of the compaction feature that holes are possible:

A previous patch in lkml has (exactly) the same fix:
http://lists-archives.com/linux-kernel/28292115-x86-xsave-c-fix-xstate-offsets-and-sizes-enumeration.html

Thanks.

-Fenghua