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

[dinesh chandrasekaran <dinesh_chan8@xxxxxxxxxxx>]

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.

From your reply,
I should use populate_physmap() only if that memory is exported as E820_RAM i.e if DomUs are to be restricted to specific range of the RAM.

And to use the addresses specified by the PCI BAR, I should use XEN_DOMCTL_iomem_permission.

'MEMORY' in the memory mapped IO regions obtained by reading the BAR value of the pci device.
But, wont this MEMORY be mapped to the actual RAM behind the CPU?

How could I completely avoid the RAM behind CPU and use the PCI memory for all DomUs?

Putting it simple, during boot-up process,

__  __            _____  _____                    _        _     _     
 \ \/ /___ _ __   |___ / |___ /    _   _ _ __  ___| |_ __ _| |__ | | ___
  \  // _ \ '_ \    |_ \   |_ \ __| | | | '_ \/ __| __/ _` | '_ \| |/ _ \
  /  \  __/ | | |  ___) | ___) |__| |_| | | | \__ \ || (_| | |_) | |  __/
 /_/\_\___|_| |_| |____(_)____/    \__,_|_| |_|___/\__\__,_|_.__/|_|\___|
                                                                        
(XEN)Xen version 3.3-unstable (reddy@(none)) (gcc version 4.1.1 (Gentoo4.1.1-r3)) Sat May 31 00:05:56 Local time zone must be set--see zicmanual page 2008
(XEN) Latest ChangeSet: Fri May 30 19:31:18 2008 +0100 17760:6e688d5a936b
(XEN) Command line:
(XEN) Video information:
(XEN)  VGA is text mode 80x25, font 8x16
(XEN)  VBE/DDC methods: V2; EDID transfer time: 2 seconds
(XEN) Disc information:
(XEN)  Found 1 MBR signatures
(XEN)  Found 1 EDD information structures
(XEN) Xen-e820 RAM map:
(XEN)  0000000000000000 - 0000000000094400 (usable)
(XEN)  0000000000094400 - 00000000000a0000 (reserved)
(XEN)  00000000000c2000 - 0000000000100000 (reserved)
(XEN)  0000000000100000 - 00000000cfe90000 (usable)
(XEN)  00000000cfe90000 - 00000000cfea3000 (ACPI data)
(XEN)  00000000cfea3000 - 00000000cff00000 (ACPI NVS)
(XEN)  00000000cff00000 - 00000000d0000000 (reserved)
(XEN)  00000000e0000000 - 00000000f0000000 (reserved)
(XEN)  00000000fec00000 - 00000000fec00400 (reserved)
(XEN)  00000000fee00000 - 00000000fee01000 (reserved)
(XEN)  00000000fff80000 - 0000000100000000 (reserved)
(XEN)  0000000100000000 - 0000000230000000 (usable)
(XEN)  00000000d0000000 - 00000000dfffffff (PCI_usable)             <this is the pci_device's BAR value>

Is this 256MB space from the RAM behind CPU?
or is this the address exclusiveley given to the RAM behind PCI?
Writing into this address will not require any re-mapping into CPU RAM?

Thanks,
Dinesh C


> Date: Mon, 30 Jun 2008 21:54:36 +0100
> From: gm281@xxxxxxxxx
> To: dinesh_chan8@xxxxxxxxxxx
> Subject: Re: [Xen-users] Re: [Xen-devel] Xen - Guest memory allocation
>
> Here is a brief terminology overview, to clear up any naming confusion:
> - I/O pages: memory in the memory mapped IO regions (a.k.a. IO memory)
> - 'real' memory: RAM
>
> > But let the Dom0 take care of I/O pages for all DomUs (hope this is the
> > default).
>
> By default Dom0 is allowed to access any IO memory, and DomUs aren't
> allowed to access any IO memory. In your email from 20th June you
> indicated that you want to allow DomUs to access certain IO memory
> range. In my previous email I suggested to look at using
> XEN_DOMCTL_iomem_permission to achieve that. You don't need to change
> populate_physmap to get that working I believe (I'm assuming PV domain
> here).
>
> > I'm just trying for the making Memory pages and NOT I/O pages for all DomUs
> > available from the my_pci address range
> > using populate_physmap().
>
> ?. Surely you either mean: RAM outside of my_pci range, or IO memory
> from my_pci range.
>
> >> You do need 'real' memory to be assigned to DomU.
> > Yeah. That is the reason why I used maddr_to_page() macro;
> >
> > I assume that xen uses populate_physmap() to allocate 'real' memory for all
> > DomUs.
> > Is my assumption wrong?
>
> Correct. populate_physmap() allocates RAM.
>
> Cheers
> Gr(z)egor(z)

---

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