linux-kernel - RE: [Qemu-devel] [PATCH v2 3/3] X86, mpx: Intel MPX xstate feature definition

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Message-ID: <DE8DF0795D48FD4CA783C40EC82923350140BB62@SHSMSX101.ccr.corp.intel.com>
Date:	Fri, 6 Dec 2013 22:12:30 +0000
From:	"Liu, Jinsong" <jinsong.liu@...el.com>
To:	"H. Peter Anvin" <hpa@...or.com>,
	Paolo Bonzini <pbonzini@...hat.com>,
	"Ren, Qiaowei" <qiaowei.ren@...el.com>
CC:	"kvm@...r.kernel.org" <kvm@...r.kernel.org>,
	"x86@...nel.org" <x86@...nel.org>,
	Xudong Hao <xudong.hao@...el.com>,
	"qemu-devel@...gnu.org" <qemu-devel@...gnu.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	Ingo Molnar <mingo@...nel.org>,
	"Thomas Gleixner" <tglx@...utronix.de>
Subject: RE: [Qemu-devel] [PATCH v2 3/3] X86,	mpx: Intel MPX xstate feature
 definition

H. Peter Anvin wrote:
> On 12/06/2013 12:05 PM, Liu, Jinsong wrote:
>>> 
>>> Since Peter already said the same, please undo these changes.
>>> 
>>> Also, how is XSTATE_EAGER used?  Should MPX be disabled when
>>> xsaveopt is disabled on the kernel command line?  (Liu, how would
>>> this affect the KVM patches, too?) 
>>> 
>>> Paolo
>> 
>> Currently seems no, and if needed we can add a new patch at kvm side
>> accordingly when native mpx patches checked in. 
>> 
> 
> We need to either disable these features in lazy mode, or we need to
> force eager mode if these features are to be supported.  The problem
> with the latter is that it means forcing eager mode regardless of if
> anything actually *uses* these features.
> 
> A third option would be to require applications to use a prctl() or
> similar to enable eager-save features.
> 
> Thoughts?
> 
> 	-hpa

The third option seems better -- how does native mpx patches work, force eager?

Thanks,
Jinsong--
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