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

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Date:	Wed, 20 Jun 2012 17:11:06 +0800
From:	Xiao Guangrong <xiaoguangrong@...ux.vnet.ibm.com>
To:	Takuya Yoshikawa <yoshikawa.takuya@....ntt.co.jp>
CC:	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 05:02 PM, Takuya Yoshikawa wrote:

> On Wed, 20 Jun 2012 15:57:15 +0800
> Xiao Guangrong <xiaoguangrong@...ux.vnet.ibm.com> wrote:
> 
>> Introduce a common function to abstract spte write-protect to
>> cleanup the code
>>
>> Signed-off-by: Xiao Guangrong <xiaoguangrong@...ux.vnet.ibm.com>
> 
> ...
> 
>> +/* Return true if the spte is dropped. */
>> +static bool spte_write_protect(struct kvm *kvm, u64 *sptep, bool *flush)
>> +{
>> +	u64 spte = *sptep;
>> +
>> +	if (!is_writable_pte(spte))
>> +		return false;
>> +
>> +	rmap_printk("rmap_write_protect: spte %p %llx\n", sptep, *sptep);
> 
> ...
> 
>> @@ -3902,16 +3915,7 @@ void kvm_mmu_slot_remove_write_access(struct kvm *kvm, int slot)
>>  			      !is_last_spte(pt[i], sp->role.level))
>>  				continue;
>>
>> -			if (is_large_pte(pt[i])) {
>> -				drop_spte(kvm, &pt[i]);
>> -				--kvm->stat.lpages;
>> -				continue;
>> -			}
>> -
>> -			/* avoid RMW */
>> -			if (is_writable_pte(pt[i]))
>> -				mmu_spte_update(&pt[i],
>> -						pt[i] & ~PT_WRITABLE_MASK);
>> +			spte_write_protect(kvm, &pt[i], &flush);
> 
> Adding rmap_printk() here seems wrong.
> 


Strange! Why do you think it is wrong? It is just debug code.

> 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.

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