linux-kernel - Re: [PATCH 2/2] KVM: MMU: Use base

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Message-ID: <20100915084833.GH17759@amd.com>
Date:	Wed, 15 Sep 2010 10:48:33 +0200
From:	"Roedel, Joerg" <Joerg.Roedel@....com>
To:	Marcelo Tosatti <mtosatti@...hat.com>
CC:	Avi Kivity <avi@...hat.com>,
	"kvm@...r.kernel.org" <kvm@...r.kernel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 2/2] KVM: MMU: Use base_role.nxe for mmu.nx

On Tue, Sep 14, 2010 at 06:08:37PM -0400, Marcelo Tosatti wrote:
> 
> For tdp better set base_role.nxe to zero, otherwise duplicate tdp
> pagetables can be created if the guest switches between nx/non-nx.
>

This does not work because bit 63 is marked as reserved if base_role.nxe
is 0. If the walk_addr_generic function then runs with tdp enabled it
would report a set nx bit as a rsvd fault.
We also can't use is_nx() in those path because it does not distinguish
between l1 and l2 nx. Are there guests that switch the efer.nx bit
regularly enough so that it matters? If so I would suggest to drop this
patch and keep mmu.nx.

	Joerg

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