Re: [patch 00/13] RFC: out of sync shadow

Marcelo Tosatti
2008-09-08T07:24:55Z

On Sun, Sep 07, 2008 at 02:22:47PM +0300, Avi Kivity wrote:
>> VMX "bypass_guest_pf" feature on prefetch_page breaks it (since new
>> PTE writes need no TLB flush, I assume). Not sure if its worthwhile to
>> convert notrap_nonpresent -> trap_nonpresent on unshadow or just go
>> for unconditional nonpaging_prefetch_page.
>>
>>
>
> Doesn't it kill bypass_guest_pf completely? As soon as we unsync a
> page, we can't have nontrapping nonpresent ptes in it.

Yes, thats what I meant.

> We can try convertion on unsync, it does speed up demand paging.
>
>> And I think other optimizations are possible now, for example the guest
>> can be responsible for remote TLB flushing on kvm_mmu_pte_write().
>>
>
> But kvm_mmu_pte_write() is no longer called, since we unsync?

On higher level pagetables it still is. The IPI functions show high up
in profiling (probably more due to write protection, but still).