Re: [PATCH v2 2/10] KVM: MMU: fix conflict access permissions in direct sp

Avi Kivity
2010-06-28T09:43:38Z

On 06/25/2010 03:05 PM, Xiao Guangrong wrote:
> In no-direct mapping, we mark sp is 'direct' when we mapping the
> guest's larger page, but its access is encoded form upper page-struct
> entire not include the last mapping, it will cause access conflict.
>
> For example, have this mapping:
> [W]
> / PDE1 -> |---|
> P[W] | | LPA
> \ PDE2 -> |---|
> [R]
>
> P have two children, PDE1 and PDE2, both PDE1 and PDE2 mapping the
> same lage page(LPA). The P's access is WR, PDE1's access is WR,
> PDE2's access is RO(just consider read-write permissions here)
>
> When guest access PDE1, we will create a direct sp for LPA, the sp's
> access is from P, is W, then we will mark the ptes is W in this sp.
>
> Then, guest access PDE2, we will find LPA's shadow page, is the same as
> PDE's, and mark the ptes is RO.
>
> So, if guest access PDE1, the incorrect #PF is occured.
>
> Fixed by encode the last mapping access into direct shadow page
>
> And, it also cleanup the code that directly get the last level's dirty flag
>
>

Looks good, but please split the cleanup from the fix (we'll want to
backport the fix but not the cleanup).

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