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

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Message-ID: <20100701122651.GD18607@amt.cnet>
Date:	Thu, 1 Jul 2010 09:26:51 -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 list <kvm@...r.kernel.org>
Subject: Re: [PATCH v3 9/11] KVM: MMU: prefetch ptes when intercepted guest
 #PF

On Thu, Jul 01, 2010 at 08:13:40PM +0800, Xiao Guangrong wrote:
> 
> 
> 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? :-)

Fine.
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