Messages in this thread | | | Date | Mon, 28 Jun 2010 14:13:23 +0300 | From | Avi Kivity <> | Subject | Re: [PATCH v2 3/10] KVM: MMU: fix direct sp's access corruptted |
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On 06/28/2010 01:02 PM, Xiao Guangrong wrote: > > Avi Kivity wrote: > > >> Instead of adding a new bit, can you encode the protection in the direct >> sp's access bits? So we'll have one sp for read-only or >> writeable-but-not-dirty small pages, and another sp for >> writeable-and-dirty small pages. >> >> > It looks like it can't solve all problems, it fix the access corrupted, > but will cause D bit losed: > > mapping A and mapping B both are writable-and-dirty, when mapping A write > #PF occurs, the mapping is writable, then we can't set B's D bit anymore. >
If B is writeable-and-dirty, then it's D bit is already set, and we don't need to do anything.
If B is writeable-and-clean, then we'll have an spte pointing to a read-only sp, so we'll get a write fault on access and an opportunity to set the D bit.
> Anyway, i think we should re-intall the mapping when the state is changed. :-( >
When the gpte is changed from read-only to writeable or from clean to dirty, we need to update the spte, yes. But that's true for other sptes as well, not just large gptes.
-- error compiling committee.c: too many arguments to function
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