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

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Message-ID: <4C2C8674.4080607@cn.fujitsu.com>
Date:	Thu, 01 Jul 2010 20:13:40 +0800
From:	Xiao Guangrong <xiaoguangrong@...fujitsu.com>
To:	Avi Kivity <avi@...hat.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



Avi Kivity wrote:
> 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.
> 

Umm, i'll import a new function named gfn_to_pfn_many_atomic(... int *enough),
using 'enough' to indicate whether have got the all consecutive pages in the slot,
Marcelo, how about it? :-)
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