linux-kernel - Re: [PATCH 4/5] KVM: MMU: move adjusting softmmu pte access to FNAME(page

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Date:	Wed, 21 Nov 2012 07:28:00 +0800
From:	Xiao Guangrong <xiaoguangrong@...ux.vnet.ibm.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 4/5] KVM: MMU: move adjusting softmmu pte access to FNAME(page_fault)

On 11/21/2012 06:27 AM, Marcelo Tosatti wrote:

>> @@ -544,6 +544,21 @@ static int FNAME(page_fault)(struct kvm_vcpu *vcpu, gva_t addr, u32 error_code,
>>  		return 0;
>>  	}
>>
>> +	if (write_fault && !(walker.pte_access & ACC_WRITE_MASK) &&
>> +	      !is_write_protection(vcpu) && !user_fault) {
>> +		walker.pte_access |= ACC_WRITE_MASK;
>> +		walker.pte_access &= ~ACC_USER_MASK;
>> +
>> +		/*
>> +		 * If we converted a user page to a kernel page,
>> +		 * so that the kernel can write to it when cr0.wp=0,
>> +		 * then we should prevent the kernel from executing it
>> +		 * if SMEP is enabled.
>> +		 */
>> +		if (kvm_read_cr4_bits(vcpu, X86_CR4_SMEP))
>> +			walker.pte_access &= ~ACC_EXEC_MASK;
>> +	}
>> +
> 
> What about sync_page path?

The sync_page and other prefetch paths only do read-prefetch, means
they call set_spte with write_fault = 0.

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