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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Message-ID: <20150506041339.GA12174@gmail.com>
Date:	Wed, 6 May 2015 06:13:39 +0200
From:	Ingo Molnar <mingo2.kernel.org@...il.com>
To:	"Yu, Fenghua" <fenghua.yu@...el.com>
Cc:	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	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


* Yu, Fenghua <fenghua.yu@...el.com> wrote:

> > 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

Ok, and that series has some more bits as well - will merge.

Thanks,

	Ingo
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