linux-kernel - Re: [PATCH 1/2] KVM: MMU: fix ept=0/pte.u=0/pte.w=0/CR0.WP=0/CR4.SMEP=1/EFER.NX=0 combo

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Date:	Thu, 10 Mar 2016 16:46:12 +0800
From:	Xiao Guangrong <guangrong.xiao@...ux.intel.com>
To:	Paolo Bonzini <pbonzini@...hat.com>, linux-kernel@...r.kernel.org,
	kvm@...r.kernel.org
Cc:	stable@...r.kernel.org, Xiao Guangrong <guangrong.xiao@...hat.com>,
	Andy Lutomirski <luto@...capital.net>
Subject: Re: [PATCH 1/2] KVM: MMU: fix
 ept=0/pte.u=0/pte.w=0/CR0.WP=0/CR4.SMEP=1/EFER.NX=0 combo



On 03/08/2016 07:44 PM, Paolo Bonzini wrote:
> Yes, all of these are needed. :) This is admittedly a bit odd, but
> kvm-unit-tests access.flat tests this if you run it with "-cpu host"
> and of course ept=0.
>
> KVM handles supervisor writes of a pte.u=0/pte.w=0/CR0.WP=0 page by
> setting U=0 and W=1 in the shadow PTE.  This will cause a user write
> to fault and a supervisor write to succeed (which is correct because
> CR0.WP=0).  A user read instead will flip U=0 to 1 and W=1 back to 0.

BTW, it should be pte.u = 1 where you mentioned above.