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

[Stefano Stabellini <stefano.stabellini@xxxxxxxxxxxxx>]

On Mon, 22 Jul 2013, David Vrabel wrote:
> 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.

I am going to go for this, avoiding any Xen side changes.

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