linux-kernel - Re: [PATCH v3 9/11] KVM: MMU: prefetch ptes when intercepted guest #PF

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Message-ID: <4C2C85E6.1050303@redhat.com>
Date:	Thu, 01 Jul 2010 15:11:18 +0300
From:	Avi Kivity <avi@...hat.com>
To:	Xiao Guangrong <xiaoguangrong@...fujitsu.com>
CC:	Marcelo Tosatti <mtosatti@...hat.com>,
	LKML <linux-kernel@...r.kernel.org>,
	KVM list <kvm@...r.kernel.org>
Subject: Re: [PATCH v3 9/11] KVM: MMU: prefetch ptes when intercepted guest
 #PF

On 07/01/2010 04:11 AM, Xiao Guangrong wrote:
>
> Marcelo Tosatti wrote:
>
>    
>>> +
>>> +		addr = gfn_to_hva_many(vcpu->kvm, gfn,&entry);
>>> +		if (kvm_is_error_hva(addr))
>>> +			return -1;
>>> +
>>> +		entry = min(entry, (int)(end - start));
>>> +		ret = __get_user_pages_fast(addr, entry, 1, pages);
>>> +		if (ret<= 0)
>>> +			return -1;
>>>        
>> Why can't you use gfn_to_pfn_atomic() here, one page at a time? Is
>> the overhead significant that this is worthwhile?
>>
>> You're bypassing the centralized interface.
>>      
> I think it's worthwhile to do since we can reduce gup overhead, no reason
> to traverse process's page table again and again for the consecutive pages.
>    

Then we should make the centralized interface work in terms of multiple 
pages, and write the single-page interfaces in terms of the multipage 
interfaces.

-- 
error compiling committee.c: too many arguments to function

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