linux-kernel - Re: [PATCH v6 5/9] KVM: MMU: introduce SPTE_MMU

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Date:	Tue, 12 Jun 2012 23:01:03 -0300
From:	Marcelo Tosatti <mtosatti@...hat.com>
To:	Xiao Guangrong <xiaoguangrong@...ux.vnet.ibm.com>
Cc:	Avi Kivity <avi@...hat.com>, LKML <linux-kernel@...r.kernel.org>,
	KVM <kvm@...r.kernel.org>
Subject: Re: [PATCH v6 5/9] KVM: MMU: introduce SPTE_MMU_WRITEABLE bit

On Tue, Jun 12, 2012 at 10:23:47AM +0800, Xiao Guangrong wrote:
> On 06/12/2012 07:32 AM, Marcelo Tosatti wrote:
> 
> > On Tue, May 29, 2012 at 02:49:14PM +0800, Xiao Guangrong wrote:
> >> This bit indicates whether the spte can be writable on MMU, that means
> >> the corresponding gpte is writable and the corresponding gfn is not
> >> protected by shadow page protection
> > 
> > Why is this still necessary, now that only sptes of direct shadow pages 
> > are updated locklessly? 
> > 
> 
> 
> Yes, but it is still needed, for nested npt/ept, we need protect
> the nested page tables.

Sure, but shadowed L1 nested pagetables are not direct shadow pages.

They are shadows of L1 nested pagetables. 

Checking sp->direct should be enough (instead of the flags).

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