Re: [PATCH v3 5/9] KVM: MMU: introduce SPTE_WRITE_PROTECT bit

From: Xiao Guangrong
Date: Sat Apr 21 2012 - 00:29:46 EST

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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