Re: [Xen-devel] [PATCH 1/5] xen/netback: Use xenballooned pages for comms

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

On Mon, Oct 24, 2011 at 05:47:40PM -0400, Daniel De Graaf wrote:
> On 10/24/2011 05:40 PM, Konrad Rzeszutek Wilk wrote:
> >> (Will move to commit message). In PV guests, it is sufficient to only
> >> reserve kernel address space for grant mappings because Xen modifies the
> >> mappings directly. HVM guests require that Xen modify the GFN-to-MFN
> >> mapping, so the pages being remapped must already be allocated. Pages
> > 
> > By allocated you mean the populate_physmap hypercall must happen before
> > the grant operations are done?
> > 
> > (When I see allocated I think alloc_page, which I believe is _not_ what
> > you were saying).
> 
> The pages must be valid kernel pages (with GFNs) which are actually obtained
> with alloc_page if the balloon doesn't have any sitting around for us. They
> must also *not* be populated in the physmap, which is why we grab them from
> the balloon and not from alloc_page directly.

Uh, aren't pages from alloc_page ("if the balloon does not have any sitting 
around
for us") obtained from normal memory that is allocated at startup. And at 
startup
those swaths of memory are obtained by populate_physmap call?


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