Re: Is there shadow page table cache during context switch?

[Xiao Guangrong <xiaoguangrong@cn.fujitsu.com>]

Gu, Zhongshu wrote:
> Hi all:
>          Recently i am looking at the code of the implementation of
> shadow page table of kvm. There is one thing that i am confused. Is
> there implementation for caching the shadow page table during context
> switch? From the code, when there is action of setting cr3 in the
> guest os, it will call new_cr3 which will free the mmu roots. When
> entering the guest again, because the root pages are invalid page now,
> it will load mmu and allocate roots again. So for every context
> switch, the shadow page table will be re-constructed. Is that right?
> 

Generally, The old mmu root is not freed, is still in shadow page cache,
then when the guest switch to the old root, it can find the corresponding
shadow page form the cache, unless the old root's shadow page is invalid
(it's zapped for the shadow page number control)