linux-kernel - RE: [PATCH v2 0/4] Enable SMEP CPU Feature

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Date:	Thu, 19 May 2011 14:10:51 +0800
From:	"Tian, Kevin" <kevin.tian@...el.com>
To:	Avi Kivity <avi@...hat.com>, Ingo Molnar <mingo@...e.hu>
CC:	"H. Peter Anvin" <hpa@...or.com>,
	"Yu, Fenghua" <fenghua.yu@...el.com>,
	Thomas Gleixner <tglx@...utronix.de>,
	"Mallick, Asit K" <asit.k.mallick@...el.com>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Arjan van de Ven <arjan@...radead.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Andi Kleen <andi@...stfloor.org>,
	linux-kernel <linux-kernel@...r.kernel.org>,
	Pekka Enberg <penberg@...helsinki.fi>,
	"Shan, Haitao" <haitao.shan@...el.com>
Subject: RE: [PATCH v2 0/4] Enable SMEP CPU Feature

> From: Avi Kivity
> Sent: Tuesday, May 17, 2011 7:34 PM
> 
> On 05/17/2011 01:46 PM, Ingo Molnar wrote:
> > >
> > >  We could support it as a non-default feature, but that reduces its utility.
> >
> > It would be a nice touch for tools/kvm/: we would use KVM_GET_SREGS
> > and KVM_GET_SREGS to twiddle CR4.SMEP, even without the guest explicitly
> doing it.
> >
> > A quick glance suggests that it could be done straight away in
> > tools/kvm/kvm-cpu.c::kvm_cpu__setup_sregs() during vcpu setup, and
> > hopefully that cr4 value survives boot and ends up in the guest
> > kernel's mmu_cr4_features mask shadow register.
> 
> Depends if the guest uses a read-modify-write pattern or not.  We could do it
> transparently in kvm.ko, since the real cr4 need not corresponds to the guest
> notion (for example, we often set cr0.wp or cr0.ts even though the guest wants
> them clear).
> 

We have a patch in hand now to enable SMEP for kvm guest, which is under 
test and cleanup and will be sent out soon. Basically it contains the basic
idea by exposing CR4.smep and cpuid leaf. Above idea is nice and we'll try 
that in a following work.

Thanks
Kevin
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