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

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Date:	Tue, 5 May 2015 23:04:41 +0000
From:	"Yu, Fenghua" <fenghua.yu@...el.com>
To:	Ingo Molnar <mingo@...nel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
CC:	Andy Lutomirski <luto@...capital.net>,
	Borislav Petkov <bp@...en8.de>,
	Dave Hansen <dave.hansen@...ux.intel.com>,
	"H. Peter Anvin" <hpa@...or.com>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Oleg Nesterov <oleg@...hat.com>,
	Thomas Gleixner <tglx@...utronix.de>
Subject: RE: [PATCH 200/208] x86/fpu/xstate: Don't assume the first zero
 xfeatures zero bit means the end

> From: Ingo Molnar [mailto:mingo.kernel.org@...il.com] On Behalf Of Ingo
> Molnar
> Sent: Tuesday, May 05, 2015 10:58 AM
> To: linux-kernel@...r.kernel.org
> 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