linux-kernel - Re: [PATCH 02/13] KVM: MMU: abstract spte write-protect

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Date:	Thu, 29 Mar 2012 19:51:25 +0800
From:	Xiao Guangrong <xiaoguangrong@...ux.vnet.ibm.com>
To:	Avi Kivity <avi@...hat.com>
CC:	Marcelo Tosatti <mtosatti@...hat.com>,
	LKML <linux-kernel@...r.kernel.org>, KVM <kvm@...r.kernel.org>
Subject: Re: [PATCH 02/13] KVM: MMU: abstract spte write-protect

On 03/29/2012 07:11 PM, Avi Kivity wrote:


>> +/* Return true if the spte is dropped. */
>> +static bool spte_write_protect(struct kvm *kvm, u64 *sptep, bool large,
>> +			       int *flush)
> 
> bool *flush
> 


Okay, will fix.

>> +{
>> +	u64 spte = *sptep;
>> +
>> +	if (!is_writable_pte(spte))
>> +		return false;
>> +
>> +	*flush |= true;
>> +
>> +	if (large) {
>> +		pgprintk("rmap_write_protect(large): spte %p %llx\n",
>> +			 spte, *spte);
>> +		BUG_ON(!is_large_pte(spte));
>> +
>> +		drop_spte(kvm, sptep);
>> +		--kvm->stat.lpages;
>> +		return true;
>> +	}
> 
> As I mentioned before, write-protecting a large spte is a good idea,
> since it moves some work from protect-time to fault-time, so it reduces
> jitter.  This removes the need for the return value.
> 
> It may also be a good idea to populate the lower level instead of
> dropping the spte.
> 
> All outside this patch set of course.  I'd add those ideas to the wiki
> but it won't let me edit at the moment.
> 


I saw your idea, i will pick it up after this patch if no one does it
at that time. :)

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