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

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Date:	Sat, 16 Mar 2013 11:06:12 +0900
From:	Takuya Yoshikawa <takuya.yoshikawa@...il.com>
To:	Xiao Guangrong <xiaoguangrong@...ux.vnet.ibm.com>
Cc:	Marcelo Tosatti <mtosatti@...hat.com>,
	Gleb Natapov <gleb@...hat.com>,
	LKML <linux-kernel@...r.kernel.org>, KVM <kvm@...r.kernel.org>
Subject: Re: [PATCH 0/5] KVM: MMU: fast invalid all mmio sptes

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@...ux.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@...il.com>
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