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

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Message-ID: <20100915144801.GA14336@amt.cnet>
Date:	Wed, 15 Sep 2010 11:48:01 -0300
From:	Marcelo Tosatti <mtosatti@...hat.com>
To:	"Roedel, Joerg" <Joerg.Roedel@....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 Wed, Sep 15, 2010 at 10:48:33AM +0200, Roedel, Joerg wrote:
> 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.

Ah, OK.

> 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.

Well, i don't think it would be a common scenario. Ignore me.

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