RE: [Xen-users] Re: [Xen-devel] Xen - Guest memory allocation

[dinesh chandrasekaran <dinesh_chan8@xxxxxxxxxxx>]

Hi Milos,
                Now the domU have access to the MMIO region using iomem_permit_access().
It can read and write successfully to this region.

But when I tried to allocate the region for booting up a domU, I get the following error

Using config file "/home/domU_confs/Linux_VM1.conf".
Error: (4, 'Out of memory', "xc_dom_boot_mem_init: can't allocate low memory for domain\n")

the mem allocation code in /xen/common/memory.c is modified to be,

if(d->is_privileged) {
                page = alloc_domheap_pages(d, a->extent_order, a->memflags);
                mfn = page_to_mfn(page);
        }

       else {
                mfn = maddr_to_mfn(mem_start);
                mem_start += PAGE_SIZE;
       }

where mem_start is the MMIO starting address (0x90000000).

>However, you'll
> have to teach the domain build tools to recognise the difference
> between RAM and MMIO (it might be as simple as patching
> direct_remap_pfn_range in linux kernel to use DOMID_IO)

By this do you mean that I should modify the Dom0 kernel.
Correct me I am wrong (I guess it is the domU kernel).

regards,
Dinesh C

> Date: Tue, 1 Jul 2008 10:46:12 +0100
> From:
> To: dinesh_chan8@xxxxxxxxxxx
> Subject: Re: [Xen-users] Re: [Xen-devel] Xen - Guest memory allocation
>
> > Okay.
> > But I want to use 'I/O pages: memory in the memory mapped IO
> > regions obtained by reading the BAR value from the pci device'
> > as the 'real' memory for all DomUs since I have 256MB behind that device.
>
> The problem you'll have to face is the ownership model that Xen uses.
> By default when RAM is allocated to a domain it is only accessible to
> the domain itself + Dom0 (via foreign mapping mechanism). All non-RAM
> ranges are allocated to a synthetic domain called dom_io. Any
> pagetables that reference this memory are verified against the
> permitted iomem range (look iomem_access_permitted()). By default
> Dom0's access is permitted, so you are fine there. However, you'll
> have to teach the domain build tools to recognise the difference
> between RAM and MMIO (it might be as simple as patching
> direct_remap_pfn_range in linux kernel to use DOMID_IO). Also, another
> concern I'd have, is if the CPU will be happy to use MMIO for code and
> stack segments. I don't know enough about that to answer.
>
> CHeers
> Gr(z)egor(z)

---

Windows Live Messenger. Multitasking at its finest.

_______________________________________________
Xen-devel mailing list
Xen-devel@xxxxxxxxxxxxxxxxxxx
http://lists.xensource.com/xen-devel