Re: [Xen-devel] (v2) Design proposal for RMRR fix

[Konrad Rzeszutek Wilk <konrad.wilk@xxxxxxxxxx>]

On Thu, Jan 15, 2015 at 08:09:34AM +0000, Tian, Kevin wrote:
> > From: Konrad Rzeszutek Wilk [mailto:konrad.wilk@xxxxxxxxxx]
> > Sent: Thursday, January 15, 2015 4:43 AM
> > 
> > On Wed, Jan 14, 2015 at 08:13:14AM +0000, Tian, Kevin wrote:
> > > > From: Konrad Rzeszutek Wilk [mailto:konrad.wilk@xxxxxxxxxx]
> > > > Sent: Wednesday, January 14, 2015 12:46 AM
> > > >
> > > >
> > > > Perhaps an easier way of this is to use the existing
> > > > mechanism we have - that is the XENMEM_memory_map (which
> > > > BTW e820_host uses). If all of this is done in the libxl (which
> > > > already does this based on the host E820, thought it can
> > > > be modified to query the hypervisor for other 'reserved
> > > > regions') and hvmloader is modified to use XENMEM_memory_map
> > > > and base its E820 on that (and also QEMU-xen), then we solve
> > > > this problem and also the http://bugs.xenproject.org/xen/bug/28?
> > > >
> > >
> > > I'm not familiar with that option, but a quick search looks saying
> > > it's only for PV guest?
> > 
> > It was originally for PV, but the hypercall can be executed under
> > HVM now too (thanks for PVH patches).
> > >
> > > and please note XENMEM_memory_map only includes RAM entries
> > > (looks also only for pv), while following above intention what we
> > > really want is real e820_host w/ all entries filled.
> > 
> > It includeds whatever we want to put in there. It can have
> > RAM, RSV, etc. That is what  e820_host does for PV guests - it fills
> > it out with an E820 that looks like the real thing.
> > 
> 
> Thanks for help me understand the status. So if we want to use this
> interface, the major work would be in the caller (e.g. hvmloader)
> to favor that layout.

Right, and it would also help in other situations (such as when
doing PCI passthrough in HVM guests with some inflexible PCIe devices
that really want an 1-1 BAR mapping - which this would help with).

> 
> Kevin

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