Re: [Xen-devel] Accessing Dom0 Physical memory from xen, via direct mappings (PML4:262-271)

[Tim Deegan <tim@xxxxxxx>]

At 20:04 -0700 on 13 Mar (1331669099), Shriram Rajagopalan wrote:
> On Tue, Mar 13, 2012 at 9:43 AM, Tim Deegan <tim@xxxxxxx> wrote:
> > At 09:32 -0700 on 13 Mar (1331631148), Shriram Rajagopalan wrote:
> > > Can I have xen allocate this huge buffer ? (a byte per 8-byte word means
> > > about
> > > 128M for a 1G guest). And if I were to have this byte-map per-vcpu, it
> > > would mean
> > > 512M worth of RAM, for a 4-vcpu guest.
> > >
> > > Is there a way I could increase the xen heap size to be able to allocate
> > > this much memory?
> >
> > IIRC on x64 xen heap is the same as domheap so it already includes all
> > free space.  Or you could pick a 1GB region at boot time, make sure it
> > doesn't get given to the memory allocators, and then mark it all as
> > owned by dom0 in the frametable.
> >
> >
> xen heap seems to be the same domheap. however, when I try to allocate
> more than 128MB of memory, it punts!
>  I am using the alloc_xenheap_pages(order, 0).
> Am I missing something here ?
> 
> I am not sure if Andres' XENMEM_exchange mechanism allows >128MB.

It has to use the allocator to get the contiguous memory, so if you
can't get that memory directle, xenmem_exchange won't work either.

Tim.

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