RE: [Xen-devel] address mapping between domains

["Ian Pratt" <m+Ian.Pratt@xxxxxxxxxxxx>]

> > The domain that's controlling the real device (usually 
> dom0) maps the domU's 
> > memory before putting data into it (either directly or using PIO).
> 
> Surely this could be optimised by (on a 64 bit system) mapping
> all of physical memory into dom0 kernel virtual memory, so it
> doesn't need to bother mapping and unmapping pages that IO is
> being done to ?

At the expense of protection, yes.

With sane DMA-capable hardware the driver domain never needs to actually
map the page into its address space anyhow. However, the grant table
stuff will still be required to enable us to configure the IO MMU
appropriately to allow the DMA (we expect to see such h/w support become
commonplace). 

Ian


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