linux-kernel - Re: [PATCH v3 04/19] KVM: MMU: cache mmio info on page fault path

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Message-ID: <4E13B7A1.9010504@cn.fujitsu.com>
Date:	Wed, 06 Jul 2011 09:17:21 +0800
From:	Xiao Guangrong <xiaoguangrong@...fujitsu.com>
To:	Marcelo Tosatti <mtosatti@...hat.com>
CC:	Avi Kivity <avi@...hat.com>, LKML <linux-kernel@...r.kernel.org>,
	KVM <kvm@...r.kernel.org>
Subject: Re: [PATCH v3 04/19] KVM: MMU: cache mmio info on page fault path

On 07/06/2011 03:04 AM, Marcelo Tosatti wrote:
		return 0;
>>  
>>  	/* mmio */
>> -	if (is_error_pfn(pfn))
>> -		return kvm_handle_bad_page(vcpu->kvm, walker.gfn, pfn);
>> +	if (is_error_pfn(pfn)) {
>> +		unsigned access = walker.pte_access;
>> +		bool dirty = is_dirty_gpte(walker.ptes[walker.level - 1]);
>> +
>> +		if (dirty)
>> +			access &= ~ACC_WRITE_MASK;
>> +
>> +		return kvm_handle_bad_page(vcpu, mmu_is_nested(vcpu) ? 0 :
>> +					   addr, access, walker.gfn, pfn);
>> +	}
> 
> Don't get this... if guest pte is dirty you cache without allowing
> write access? Why?
> 

Ah, sorry, the logic should be: if pte is not diry, clear write access,
will fix it. Thanks, Marcelo!

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