Re: [Xen-devel] [PATCH v5 4/4] xen: introduce XENMEM_exchange_and_pin and XENMEM_unpin

[Ian Campbell <Ian.Campbell@xxxxxxxxxx>]

On Tue, 2013-09-10 at 13:15 +0100, Jan Beulich wrote:

> > @@ -459,6 +460,52 @@ DEFINE_XEN_GUEST_HANDLE(xen_mem_sharing_op_t);
> >   * The zero value is appropiate.
> >   */
> >  
> > +#define XENMEM_exchange_and_pin             26
> > +/*
> > + * This hypercall is similar to XENMEM_exchange: it takes the same
> > + * struct as an argument and it exchanges the pages passed in with a new
> > + * set of pages. The new pages are going to be "pinned": it's guaranteed
> > + * that their p2m mapping won't be changed until explicitly "unpinned".
> > + * The content of the exchanged pages is lost.
> > + * Only normal guest r/w memory can be pinned: no granted pages or
> > + * ballooned pages.
> > + * If return code is zero then @out.extent_list provides the DMA frame
> > + * numbers of the newly-allocated memory.
> 
> "DMA"? I don't think that term is universally true across all possible
> architectures (but we're in an architecture independent header
> here). "Machine" would probably be better (as it implies CPU
> perspective, whereas DMA hints at device perspective).

I think DMA here is correct. The purpose of exchange and pin is so that
the page can be safely handed to a device for DMA.

On an architecture where DMA address != Machine address then this should
indeed return the DMA addresses.

Ian.


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