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

Marcelo Tosatti
2010-07-01T12:27:58Z

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.