On 06/09/2011 03:39 PM, Avi Kivity wrote:
> First, I think we should consider dropping bypass_guest_pf completely, just
> so we have less things to think about.
>
I agree.
> I'm also not sure RCU is enough protection - we can unlink a page in the
> middle of a hierarchy,
I think it is ok, it just likes the page structure cache of real CPU, we can use
the old mapping or new mapping here, if we missed, page fault path is called,
it can
fix the problem for us.
> and on i386 this causes an invalid pointer to appear when we fetch the two
> halves. But I guess, if the cpu can do it, so can we.
>
Ah, maybe the cpu can not do it, we need a light way to get spte for i386
host...
> Maybe we can do something like
>
> again:
> fetch pointer to last level spte using RCU
> if failed:
> take lock
> build spte hierarchy
> drop lock
> goto again
> if sync:
> if mmio:
> do mmio
> return
> return
> walk guest table
> install spte
> if mmio:
> do mmio
>
> (sync is always false for tdp)
>
It seams it is more complex, the origin way is:
fetch last level spte
if failed or it is not a mmio spte:
call page fault
do mmio
and it has little heavy sine we need to walk guest page table,
and build spte under mmu-lock.
Maybe i missed your meaning, could you please tell me the advantage? :-(
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