linux-kernel - Re: [PATCH v3 5/9] KVM: MMU: introduce SPTE_WRITE

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Date:	Sat, 21 Apr 2012 12:29:44 +0800
From:	Xiao Guangrong <xiaoguangrong.eric@...il.com>
To:	Marcelo Tosatti <mtosatti@...hat.com>
CC:	Xiao Guangrong <xiaoguangrong@...ux.vnet.ibm.com>,
	Avi Kivity <avi@...hat.com>,
	LKML <linux-kernel@...r.kernel.org>, KVM <kvm@...r.kernel.org>
Subject: Re: [PATCH v3 5/9] KVM: MMU: introduce SPTE_WRITE_PROTECT bit

On 04/21/2012 08:55 AM, Marcelo Tosatti wrote:


>> So this is an example of implicit assumptions which break if you update
>> spte without mmu_lock. Certainly there are more cases. :(
> 
> OK, i now see you mentioned a similar case in the document, for
> rmap_write_protect.
> 
> More importantly than the particular flush TLB case, the point is
> every piece of code that reads and writes sptes must now be aware that
> mmu_lock alone does not guarantee stability. Everything must be audited.
> 


Yes, that is true, but it is not hard to audit the code since we only
change the spte from read-only to writable, also all information that
fast page fault depends on is from spte.

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