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

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Message-ID: <51073A1C.1050600@linux.vnet.ibm.com>
Date:	Tue, 29 Jan 2013 10:55:24 +0800
From:	Xiao Guangrong <xiaoguangrong@...ux.vnet.ibm.com>
To:	Marcelo Tosatti <mtosatti@...hat.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 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".


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

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