Re: [Xen-devel] [RFC][PATCH 02/13] introduce XENMEM_reserved_device_memory_map

["Tian, Kevin" <kevin.tian@xxxxxxxxx>]

> From: Tim Deegan [mailto:tim@xxxxxxx]
> Sent: Thursday, April 16, 2015 11:24 PM
> 
> At 16:10 +0100 on 16 Apr (1429200644), Jan Beulich wrote:
> > >>> On 16.04.15 at 16:59, <tim@xxxxxxx> wrote:
> > > At 17:21 +0800 on 10 Apr (1428686513), Tiejun Chen wrote:
> > >> diff --git a/xen/include/public/memory.h b/xen/include/public/memory.h
> > >> index 2b5206b..36e5f54 100644
> > >> --- a/xen/include/public/memory.h
> > >> +++ b/xen/include/public/memory.h
> > >> @@ -574,7 +574,37 @@ struct xen_vnuma_topology_info {
> > >>  typedef struct xen_vnuma_topology_info xen_vnuma_topology_info_t;
> > >>  DEFINE_XEN_GUEST_HANDLE(xen_vnuma_topology_info_t);
> > >>
> > >> -/* Next available subop number is 27 */
> > >> +/*
> > >> + * For legacy reasons, some devices must be configured with special
> memory
> > >> + * regions to function correctly.  The guest would take these regions
> > >> + * according to different user policies.
> > >> + */
> > >
> > > I don't understand what this means.  Can you try to write a comment
> > > that would tell an OS developer:
> > >  - what the reserved device memory map actually means; and
> > >  - what this hypercall does.
> >
> > For one, this is meant to be a tools only interface, hence the OS
> > developer shouldn't care much. And then I don't think we should
> > be explaining the RMRR concept here.
> 
> Fair enough.  How about:
> 
> /*
>  * On some legacy devices, certain guest-physical addresses cannot
>  * safely be used to map guest RAM.  This hypercall enumerates those
>  * regions so the toolstack can avoid using them.
>  */
> 

to be accurate it's not only about "used to map guest RAM". It's about
"allocated for any use including guest RAM, PCI BAR, etc.". How about:

/*
 * On some legacy devices, certain guest-physical addresses must be 
 * reserved in gfn space which cannot safely be used for other purposes
 * e.g. to map guest RAM.  This hypercall enumerates those regions 
 * so the toolstack can avoid using them.
 */

Thanks
Kevin

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