Re: [Xen-devel] [PATCH 0/3] make ballooned out pages have a valid mapping at all times

[David Vrabel <david.vrabel@xxxxxxxxxx>]

On 21/07/13 18:32, Stefano Stabellini wrote:
> Hi all,
> this patch series limits problems caused by tcp retransmits on NFS when
> the original block pages were mapped from a foreign domain and now the
> mapping is gone.
> 
> It accomplishes the goal by:
> 
> 1) mapping all ballooned out pages to a "balloon_trade_page";
> 2) making sure that once a grant is unmapped, the original mapping to
> balloon_trade_page is restored atomically.

I think this can be fixed without any hypervisor-side changes, although
hypervisor changes will allow you to do it more efficiently.

Use a per-CPU set of trade pages.

Note MFN of this CPU's trade page (trade_mfn).
Do the grant_unmap_and_replace(), (trade page mapping's MFN is cleared
but this is ok as nothing is accessing the page via this mapping).
update_va_mapping on trade page VA to set its MFN to trade_mfn.

David

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