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xen-devel
RE: [Xen-devel] 2MB page PV guest support clarification
> You remark about aliasing prompts me to ask a general question about
> that. I am currently mapping physical to virtual 1-1 (because that is
> what minis-os has always done) as well as mapping parts of that to
> other areas in virtual memory. Both of these are RW mappings. Is that
> ok? It perfectly possible for me to unmap the 1-1 mappings or make them
> RO if I have to.
Any page that is part of a pagetable must be mapped RO in every mapping to it.
Attempting to add a page that has RW mappings to a pagetable will fail (either
when you make the hypercall to add the PTE, or when you pin a constructed
pagetable or try switching to it).
Thus, you need to be careful with 1:1 maps to remove pages that may become PT
pages. It's best to have a PT page allocator that tries to allocate PT's from
contiguous regions and then recycles them.
Ian
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