linux-kernel - Re: [PATCH v7 02/10] KVM: MMU: abstract spte write-protect

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Date:	Wed, 20 Jun 2012 21:21:07 +0800
From:	Xiao Guangrong <xiaoguangrong@...ux.vnet.ibm.com>
To:	Takuya Yoshikawa <takuya.yoshikawa@...il.com>
CC:	Takuya Yoshikawa <yoshikawa.takuya@....ntt.co.jp>,
	Avi Kivity <avi@...hat.com>,
	Marcelo Tosatti <mtosatti@...hat.com>,
	LKML <linux-kernel@...r.kernel.org>, KVM <kvm@...r.kernel.org>
Subject: Re: [PATCH v7 02/10] KVM: MMU: abstract spte write-protect

On 06/20/2012 08:56 PM, Takuya Yoshikawa wrote:

> On Wed, 20 Jun 2012 17:11:06 +0800
> Xiao Guangrong <xiaoguangrong@...ux.vnet.ibm.com> wrote:
> 
>> Strange! Why do you think it is wrong? It is just debug code.
> 
> kvm_mmu_slot_remove_write_access() does not use rmap but the debug code says:
> 	rmap_printk("rmap_write_protect: spte %p %llx\n", sptep, *sptep);


It is not a problem since all sptes which are pointing to gfn is existed in rmap.

> 
>>> If you think it is not a problem, please explain why you think so in
>>> the changelog.
>>
>>
>> It is a from the first place and it is used to debug and not compiled at all.
> 
> It was not in kvm_mmu_slot_remove_write_access() before, no?
> 
> This patch says that the write protection code becomes commonly usable
> function, but it still has rmap_write_protect specific debug code in it;
> using it in kvm_mmu_slot_remove_write_access(), which is not at all related
> to rmap_write_protect, is strange.
> 
> As you say, this is just debug code and does not have any practical problem.
> But randomly putting debug code is not a good thing.
> 


Again, "rmap" does not break the logic, the spte we handle in this function must
be in rmap.

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