linux-kernel - Re: [PATCH v3 05/19] KVM: MMU: optimize to handle dirty bit

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Message-ID: <20110705192703.GB24417@amt.cnet>
Date:	Tue, 5 Jul 2011 16:27:03 -0300
From:	Marcelo Tosatti <mtosatti@...hat.com>
To:	Xiao Guangrong <xiaoguangrong@...fujitsu.com>
Cc:	Avi Kivity <avi@...hat.com>, LKML <linux-kernel@...r.kernel.org>,
	KVM <kvm@...r.kernel.org>
Subject: Re: [PATCH v3 05/19] KVM: MMU: optimize to handle dirty bit

On Thu, Jun 30, 2011 at 04:21:30PM +0800, Xiao Guangrong wrote:
> If dirty bit is not set, we can make the pte access read-only to avoid handing
> dirty bit everywhere
> 
> Signed-off-by: Xiao Guangrong <xiaoguangrong@...fujitsu.com>

> -static unsigned FNAME(gpte_access)(struct kvm_vcpu *vcpu, pt_element_t gpte)
> +static unsigned FNAME(gpte_access)(struct kvm_vcpu *vcpu, pt_element_t gpte,
> +				   bool last)
>  {
>  	unsigned access;
>  
>  	access = (gpte & (PT_WRITABLE_MASK | PT_USER_MASK)) | ACC_EXEC_MASK;
> +	if (last && !is_dirty_gpte(gpte))
> +		access &= ~ACC_WRITE_MASK;
> +

What if the walker marks the dirty bit on the gpte?

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