Re: [PATCH 0/5] KVM: MMU: fast invalid all mmio sptes

Takuya Yoshikawa
2013-03-16T02:06:21Z

Still reading, but sounds great if this works!

I did not like the idea of mmio-rmap based approach so much, but this
would be really/perfectly scalable.

Thanks,
Takuya

On Fri, 15 Mar 2013 23:26:16 +0800
Xiao Guangrong <xiaoguangrong@linux.vnet.ibm.com> wrote:

> The current way is holding hot mmu-lock and walking all shadow pages, this
> is not scale. This patchset tries to introduce a very simple and scale way
> to fast invalid all mmio sptes - it need not walk any shadow pages and hold
> any locks.
>
> The idea is simple:
> KVM maintains a global mmio invalid generation-number which is stored in
> kvm->arch.mmio_invalid_gen and every mmio spte stores the current global
> generation-number into his available bits when it is created.
>
> When KVM need zap all mmio sptes, it just simply increase the global
> generation-number. When guests do mmio access, KVM intercepts a MMIO #PF
> then it walks the shadow page table and get the mmio spte. If the
> generation-number on the spte does not equal the global generation-number,
> it will go to the normal #PF handler to update the mmio spte.
>
> Since 19 bits are used to store generation-number on mmio spte, the
> generation-number can be round after 33554432 times. It is large enough
> for nearly all most cases, but making the code be more strong, we zap all
> shadow pages when the number is round.
>
> Note: after my patchset that fast zap all shadow pages, kvm_mmu_zap_all is
> not a problem any more. The scalability is the same as zap mmio shadow page
>
>
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--
Takuya Yoshikawa <takuya.yoshikawa@gmail.com>