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From: "Ren, Qiaowei" <qiaowei.ren@intel.com>
To: "Liu, Jinsong" <jinsong.liu@intel.com>, "H. Peter Anvin" <hpa@zytor.com>,
        Paolo Bonzini <pbonzini@redhat.com>
CC: "kvm@vger.kernel.org" <kvm@vger.kernel.org>,
        "x86@kernel.org" <x86@kernel.org>, Xudong Hao <xudong.hao@intel.com>,
        "qemu-devel@nongnu.org" <qemu-devel@nongnu.org>,
        "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
        Ingo Molnar <mingo@kernel.org>, "Thomas Gleixner" <tglx@linutronix.de>
Subject: RE: [Qemu-devel] [PATCH v2 3/3] X86,	mpx: Intel MPX xstate feature
 definition
Thread-Topic: [Qemu-devel] [PATCH v2 3/3] X86,	mpx: Intel MPX xstate feature
 definition
Thread-Index: AQHO8r59I/URrjaMpE23f485Fe4/QppHKhsAgAAKzQCAAKpGYA==
Date: Sat, 7 Dec 2013 00:23:23 +0000
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> -----Original Message-----
> From: Liu, Jinsong
> Sent: Saturday, December 07, 2013 6:13 AM
> To: H. Peter Anvin; Paolo Bonzini; Ren, Qiaowei
> Cc: kvm@vger.kernel.org; x86@kernel.org; Xudong Hao;
> qemu-devel@nongnu.org; linux-kernel@vger.kernel.org; Ingo Molnar; Thomas
> Gleixner
> 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?
> 
It should be the second option, as you can see xsave.c which we remove from this patch. :)

Thanks,
Qiaowei