linux-kernel - Re: [PATCH v3 00/15] KVM: MMU: fast zap all shadow pages

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Date:	Mon, 22 Apr 2013 15:39:38 +0300
From:	Gleb Natapov <gleb@...hat.com>
To:	Marcelo Tosatti <mtosatti@...hat.com>
Cc:	Xiao Guangrong <xiaoguangrong@...ux.vnet.ibm.com>,
	avi.kivity@...il.com, linux-kernel@...r.kernel.org,
	kvm@...r.kernel.org
Subject: Re: [PATCH v3 00/15] KVM: MMU: fast zap all shadow pages

On Sun, Apr 21, 2013 at 12:35:08PM -0300, Marcelo Tosatti wrote:
> On Sun, Apr 21, 2013 at 12:27:51PM -0300, Marcelo Tosatti wrote:
> > On Sun, Apr 21, 2013 at 04:03:46PM +0300, Gleb Natapov wrote:
> > > On Tue, Apr 16, 2013 at 02:32:38PM +0800, Xiao Guangrong wrote:
> > > > This patchset is based on my previous two patchset:
> > > > [PATCH 0/2] KVM: x86: avoid potential soft lockup and unneeded mmu reload
> > > > (https://lkml.org/lkml/2013/4/1/2)
> > > > 
> > > > [PATCH v2 0/6] KVM: MMU: fast invalid all mmio sptes
> > > > (https://lkml.org/lkml/2013/4/1/134)
> > > > 
> > > > Changlog:
> > > > V3:
> > > >   completely redesign the algorithm, please see below.
> > > > 
> > > This looks pretty complicated. Is it still needed in order to avoid soft
> > > lockups after "avoid potential soft lockup and unneeded mmu reload" patch?
> > 
> > Do not want kvm_set_memory (cases: DELETE/MOVE/CREATES) to be
> > suspectible to:
> > 
> > vcpu 1    		|	kvm_set_memory
> > create shadow page 		
> > 				nuke shadow page
> > create shadow page
> > 				nuke shadow page
> > 
> > Which is guest triggerable behavior with spinlock preemption algorithm.
> 
> Not only guest triggerable as in the sense of a malicious guest, 
> but condition above can be induced by host workload with non-malicious
> guest system.
> 
Is the problem that newly created shadow pages are immediately zapped?
Shouldn't generation number/kvm_mmu_zap_all_invalid() idea described here
https://lkml.org/lkml/2013/4/22/111 solve this?

> Also kvm_set_memory being relatively fast with huge memory guests
> is nice (which is what Xiaos idea allows).
> 

--
			Gleb.
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