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

Xiao Guangrong
2010-07-01T12:17:34Z

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? :-)