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

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Message-ID: <4DD25D29.9040008@redhat.com>
Date:	Tue, 17 May 2011 14:34:01 +0300
From:	Avi Kivity <avi@...hat.com>
To:	Ingo Molnar <mingo@...e.hu>
CC:	"H. Peter Anvin" <hpa@...or.com>,
	Fenghua Yu <fenghua.yu@...el.com>,
	Thomas Gleixner <tglx@...utronix.de>,
	Asit K Mallick <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>
Subject: Re: [PATCH v2 0/4] Enable SMEP CPU Feature

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).

-- 
error compiling committee.c: too many arguments to function

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