Re: [Xen-devel] [hybrid] : mmap pfn space...

[Ian Campbell <Ian.Campbell@xxxxxxxxxx>]

On Mon, 2012-03-26 at 11:37 +0100, Stefano Stabellini wrote:
> On Fri, 23 Mar 2012, Mukesh Rathor wrote:
> > Hi Ian/Stefano,
> > 
> > So, I'm back to using pfn space from maxphysaddr below. Stefano, you
> > suggested ballooning, but that would be just too slow. There are lot of
> > pages to be mapped, 4k at a time during guest creation, and I am afraid
> > ballooning and hypercalls to populate EPT will be pretty slow.
> > 
> > OTOH, there is tons of address space available between max-physaddr and
> > max pfn in dom0. Stefano, your concern was stuff mapped there 
> > causing problems in future. But we can always look at the e820 for
> > conflicts. Keeping things fast is important for us .
> > 
> > Please let me know if you still have issues with my approach. I
> > believe this is what Ian is doing on ARM port.
> 
> I think that we should explicitly allocate these pages/addresses and
> not rely on the fact that they are at a specific location that we deem
> safe for now.

Agreed. In the context of the thing I'm doing on ARM this is entirely a
short term hack until we figure out something better.

Ian.

> So if we explicitly introduce a new region at the end of the e820 that
> we mark as reserved and we use it for this, I would be OK with that.
> However we need to be careful because editing the e820 has proved to be
> challenging in the past.
> Also we would need to figure out a way to tell Linux that these
> reserved addresses are actually OK to be used. Maybe we need a new
> command line or hypercall for that.



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