[Xen-devel] vNUMA for PV guest: kernel and toolstack interaction regarding e820_host=1

[Wei Liu <wei.liu2@xxxxxxxxxx>]

Hi all

I encounter a problem that I would like to get some advice. It's PV
specific because of the P2M manipulation is only required by PV.

Current scheme of memory allocation scheme:

1. Libxc populate contiguous chunk of pages and fill in initial P2M. The
   holes in e820 map are in fact filled with pages.

2. Guest kernel reads e820 map from Xen and remap pages in e820 holes if
   there are holes, update P2M as it sees fit. (That is normally true when
   e820_host=1 is set)

This is not very ideal for PV vNUMA, because those pages remapped may
end up in the wrong vnode.

What I have in mind is:

1. Libxc populates pages, but skips e820 holes. The initial P2M is the
   final P2M guest sees.
2. Guest kernel skips remapping. But Linux still needs to setup 1-1
   mapping for holes.

In order to avoid misconfiguration, we would need to introduce a new
feature flag to indicate guest has the ability to skip remapping. Libxc
will check that feature flag when building domain.

Does the above scheme make sense?

Wei.

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