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

[Stefano Stabellini <stefano.stabellini@xxxxxxxxxxxxx>]

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.
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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