linux-kernel - Re: [PATCH v2 03/12] KVM: MMU: simplify mmu_set

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Message-ID: <20130129215345.GA27735@amt.cnet>
Date:	Tue, 29 Jan 2013 19:53:45 -0200
From:	Marcelo Tosatti <mtosatti@...hat.com>
To:	Xiao Guangrong <xiaoguangrong@...ux.vnet.ibm.com>
Cc:	Avi Kivity <avi.kivity@...il.com>, Gleb Natapov <gleb@...hat.com>,
	LKML <linux-kernel@...r.kernel.org>, KVM <kvm@...r.kernel.org>
Subject: Re: [PATCH v2 03/12] KVM: MMU: simplify mmu_set_spte

On Tue, Jan 29, 2013 at 10:55:24AM +0800, Xiao Guangrong wrote:
> On 01/29/2013 08:21 AM, Marcelo Tosatti wrote:
> > On Wed, Jan 23, 2013 at 06:05:29PM +0800, Xiao Guangrong wrote:
> >> In order to detecting spte remapping, we can simply check whether the
> >> spte has already been pointing to the pfn even if the spte is not the
> >> last spte, for middle spte is pointing to the kernel pfn which can not
> >> be mapped to userspace
> > 
> > This check is detecting spte overwrite, when a large spte is replaced by 
> > pointer to spte table.
> > 
> > Can't see why check for different pfn is safe: only 'int level' can
> > differ, and pfn be equivalent, for example.
> 
> The 'u64 *sptep' must on the "int level" we want to set, that means:
>  page_header(__pa(sptep)).role.level == "int level".

Right, then stick a comment there noting which cases that condition handles.
Keep the current comment and add more.

> We discussed this before :), the discussion can be found at:
> http://marc.info/?l=kvm&m=135345057329427&w=2.

Note http://marc.info/?l=kvm&m=135345059929436&w=2, please take into
account in the future.

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